1	// SPDX-License-Identifier: GPL-2.0-only
2	/*
3	* fs/fs-writeback.c
4	*
5	* Copyright (C) 2002, Linus Torvalds.
6	*
7	* Contains all the functions related to writing back and waiting
8	* upon dirty inodes against superblocks, and writing back dirty
9	* pages against inodes. ie: data writeback. Writeout of the
10	* inode itself is not handled here.
11	*
12	* 10Apr2002 Andrew Morton
13	* Split out of fs/inode.c
14	* Additions for address_space-based writeback
15	*/
16
17	#include <linux/kernel.h>
18	#include <linux/export.h>
19	#include <linux/spinlock.h>
20	#include <linux/slab.h>
21	#include <linux/sched.h>
22	#include <linux/fs.h>
23	#include <linux/mm.h>
24	#include <linux/pagemap.h>
25	#include <linux/kthread.h>
26	#include <linux/writeback.h>
27	#include <linux/blkdev.h>
28	#include <linux/backing-dev.h>
29	#include <linux/tracepoint.h>
30	#include <linux/device.h>
31	#include <linux/memcontrol.h>
32	#include "internal.h"
33
34	/*
35	* 4MB minimal write chunk size
36	*/
37	#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_SHIFT - 10))
38
39	/*
40	* Passed into wb_writeback(), essentially a subset of writeback_control
41	*/
42	struct wb_writeback_work {
43	long nr_pages;
44	struct super_block *sb;
45	enum writeback_sync_modes sync_mode;
46	unsigned int tagged_writepages:1;
47	unsigned int for_kupdate:1;
48	unsigned int range_cyclic:1;
49	unsigned int for_background:1;
50	unsigned int for_sync:1; /* sync(2) WB_SYNC_ALL writeback */
51	unsigned int auto_free:1; /* free on completion */
52	enum wb_reason reason; /* why was writeback initiated? */
53
54	struct list_head list; /* pending work list */
55	struct wb_completion *done; /* set if the caller waits */
56	};
57
58	/*
59	* If an inode is constantly having its pages dirtied, but then the
60	* updates stop dirtytime_expire_interval seconds in the past, it's
61	* possible for the worst case time between when an inode has its
62	* timestamps updated and when they finally get written out to be two
63	* dirtytime_expire_intervals. We set the default to 12 hours (in
64	* seconds), which means most of the time inodes will have their
65	* timestamps written to disk after 12 hours, but in the worst case a
66	* few inodes might not their timestamps updated for 24 hours.
67	*/
68	unsigned int dirtytime_expire_interval = 12 * 60 * 60;
69
70	static inline struct inode *wb_inode(struct list_head *head)
71	{
72	return list_entry(head, struct inode, i_io_list);
73	}
74
75	/*
76	* Include the creation of the trace points after defining the
77	* wb_writeback_work structure and inline functions so that the definition
78	* remains local to this file.
79	*/
80	#define CREATE_TRACE_POINTS
81	#include <trace/events/writeback.h>
82
83	EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
84
85	static bool wb_io_lists_populated(struct bdi_writeback *wb)
86	{
87	if (wb_has_dirty_io(wb)) {
88	return false;
89	} else {
90	set_bit(nr: WB_has_dirty_io, addr: &wb->state);
91	WARN_ON_ONCE(!wb->avg_write_bandwidth);
92	atomic_long_add(i: wb->avg_write_bandwidth,
93	v: &wb->bdi->tot_write_bandwidth);
94	return true;
95	}
96	}
97
98	static void wb_io_lists_depopulated(struct bdi_writeback *wb)
99	{
100	if (wb_has_dirty_io(wb) && list_empty(head: &wb->b_dirty) &&
101	list_empty(head: &wb->b_io) && list_empty(head: &wb->b_more_io)) {
102	clear_bit(nr: WB_has_dirty_io, addr: &wb->state);
103	WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
104	&wb->bdi->tot_write_bandwidth) < 0);
105	}
106	}
107
108	/**
109	* inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
110	* @inode: inode to be moved
111	* @wb: target bdi_writeback
112	* @head: one of @wb->b_{dirty|io|more_io|dirty_time}
113	*
114	* Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
115	* Returns %true if @inode is the first occupant of the !dirty_time IO
116	* lists; otherwise, %false.
117	*/
118	static bool inode_io_list_move_locked(struct inode *inode,
119	struct bdi_writeback *wb,
120	struct list_head *head)
121	{
122	assert_spin_locked(&wb->list_lock);
123	assert_spin_locked(&inode->i_lock);
124	WARN_ON_ONCE(inode->i_state & I_FREEING);
125
126	list_move(list: &inode->i_io_list, head);
127
128	/* dirty_time doesn't count as dirty_io until expiration */
129	if (head != &wb->b_dirty_time)
130	return wb_io_lists_populated(wb);
131
132	wb_io_lists_depopulated(wb);
133	return false;
134	}
135
136	static void wb_wakeup(struct bdi_writeback *wb)
137	{
138	spin_lock_irq(lock: &wb->work_lock);
139	if (test_bit(WB_registered, &wb->state))
140	mod_delayed_work(wq: bdi_wq, dwork: &wb->dwork, delay: 0);
141	spin_unlock_irq(lock: &wb->work_lock);
142	}
143
144	/*
145	* This function is used when the first inode for this wb is marked dirty. It
146	* wakes-up the corresponding bdi thread which should then take care of the
147	* periodic background write-out of dirty inodes. Since the write-out would
148	* starts only 'dirty_writeback_interval' centisecs from now anyway, we just
149	* set up a timer which wakes the bdi thread up later.
150	*
151	* Note, we wouldn't bother setting up the timer, but this function is on the
152	* fast-path (used by '__mark_inode_dirty()'), so we save few context switches
153	* by delaying the wake-up.
154	*
155	* We have to be careful not to postpone flush work if it is scheduled for
156	* earlier. Thus we use queue_delayed_work().
157	*/
158	static void wb_wakeup_delayed(struct bdi_writeback *wb)
159	{
160	unsigned long timeout;
161
162	timeout = msecs_to_jiffies(m: dirty_writeback_interval * 10);
163	spin_lock_irq(lock: &wb->work_lock);
164	if (test_bit(WB_registered, &wb->state))
165	queue_delayed_work(wq: bdi_wq, dwork: &wb->dwork, delay: timeout);
166	spin_unlock_irq(lock: &wb->work_lock);
167	}
168
169	static void finish_writeback_work(struct bdi_writeback *wb,
170	struct wb_writeback_work *work)
171	{
172	struct wb_completion *done = work->done;
173
174	if (work->auto_free)
175	kfree(objp: work);
176	if (done) {
177	wait_queue_head_t *waitq = done->waitq;
178
179	/* @done can't be accessed after the following dec */
180	if (atomic_dec_and_test(v: &done->cnt))
181	wake_up_all(waitq);
182	}
183	}
184
185	static void wb_queue_work(struct bdi_writeback *wb,
186	struct wb_writeback_work *work)
187	{
188	trace_writeback_queue(wb, work);
189
190	if (work->done)
191	atomic_inc(v: &work->done->cnt);
192
193	spin_lock_irq(lock: &wb->work_lock);
194
195	if (test_bit(WB_registered, &wb->state)) {
196	list_add_tail(new: &work->list, head: &wb->work_list);
197	mod_delayed_work(wq: bdi_wq, dwork: &wb->dwork, delay: 0);
198	} else
199	finish_writeback_work(wb, work);
200
201	spin_unlock_irq(lock: &wb->work_lock);
202	}
203
204	/**
205	* wb_wait_for_completion - wait for completion of bdi_writeback_works
206	* @done: target wb_completion
207	*
208	* Wait for one or more work items issued to @bdi with their ->done field
209	* set to @done, which should have been initialized with
210	* DEFINE_WB_COMPLETION(). This function returns after all such work items
211	* are completed. Work items which are waited upon aren't freed
212	* automatically on completion.
213	*/
214	void wb_wait_for_completion(struct wb_completion *done)
215	{
216	atomic_dec(v: &done->cnt); /* put down the initial count */
217	wait_event(*done->waitq, !atomic_read(&done->cnt));
218	}
219
220	#ifdef CONFIG_CGROUP_WRITEBACK
221
222	/*
223	* Parameters for foreign inode detection, see wbc_detach_inode() to see
224	* how they're used.
225	*
226	* These paramters are inherently heuristical as the detection target
227	* itself is fuzzy. All we want to do is detaching an inode from the
228	* current owner if it's being written to by some other cgroups too much.
229	*
230	* The current cgroup writeback is built on the assumption that multiple
231	* cgroups writing to the same inode concurrently is very rare and a mode
232	* of operation which isn't well supported. As such, the goal is not
233	* taking too long when a different cgroup takes over an inode while
234	* avoiding too aggressive flip-flops from occasional foreign writes.
235	*
236	* We record, very roughly, 2s worth of IO time history and if more than
237	* half of that is foreign, trigger the switch. The recording is quantized
238	* to 16 slots. To avoid tiny writes from swinging the decision too much,
239	* writes smaller than 1/8 of avg size are ignored.
240	*/
241	#define WB_FRN_TIME_SHIFT 13 /* 1s = 2^13, upto 8 secs w/ 16bit */
242	#define WB_FRN_TIME_AVG_SHIFT 3 /* avg = avg * 7/8 + new * 1/8 */
243	#define WB_FRN_TIME_CUT_DIV 8 /* ignore rounds < avg / 8 */
244	#define WB_FRN_TIME_PERIOD (2 * (1 << WB_FRN_TIME_SHIFT)) /* 2s */
245
246	#define WB_FRN_HIST_SLOTS 16 /* inode->i_wb_frn_history is 16bit */
247	#define WB_FRN_HIST_UNIT (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
248	/* each slot's duration is 2s / 16 */
249	#define WB_FRN_HIST_THR_SLOTS (WB_FRN_HIST_SLOTS / 2)
250	/* if foreign slots >= 8, switch */
251	#define WB_FRN_HIST_MAX_SLOTS (WB_FRN_HIST_THR_SLOTS / 2 + 1)
252	/* one round can affect upto 5 slots */
253	#define WB_FRN_MAX_IN_FLIGHT 1024 /* don't queue too many concurrently */
254
255	/*
256	* Maximum inodes per isw. A specific value has been chosen to make
257	* struct inode_switch_wbs_context fit into 1024 bytes kmalloc.
258	*/
259	#define WB_MAX_INODES_PER_ISW ((1024UL - sizeof(struct inode_switch_wbs_context)) \
260	/ sizeof(struct inode *))
261
262	static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
263	static struct workqueue_struct *isw_wq;
264
265	void __inode_attach_wb(struct inode *inode, struct folio *folio)
266	{
267	struct backing_dev_info *bdi = inode_to_bdi(inode);
268	struct bdi_writeback *wb = NULL;
269
270	if (inode_cgwb_enabled(inode)) {
271	struct cgroup_subsys_state *memcg_css;
272
273	if (folio) {
274	memcg_css = mem_cgroup_css_from_folio(folio);
275	wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
276	} else {
277	/* must pin memcg_css, see wb_get_create() */
278	memcg_css = task_get_css(current, subsys_id: memory_cgrp_id);
279	wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
280	css_put(css: memcg_css);
281	}
282	}
283
284	if (!wb)
285	wb = &bdi->wb;
286
287	/*
288	* There may be multiple instances of this function racing to
289	* update the same inode. Use cmpxchg() to tell the winner.
290	*/
291	if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
292	wb_put(wb);
293	}
294	EXPORT_SYMBOL_GPL(__inode_attach_wb);
295
296	/**
297	* inode_cgwb_move_to_attached - put the inode onto wb->b_attached list
298	* @inode: inode of interest with i_lock held
299	* @wb: target bdi_writeback
300	*
301	* Remove the inode from wb's io lists and if necessarily put onto b_attached
302	* list. Only inodes attached to cgwb's are kept on this list.
303	*/
304	static void inode_cgwb_move_to_attached(struct inode *inode,
305	struct bdi_writeback *wb)
306	{
307	assert_spin_locked(&wb->list_lock);
308	assert_spin_locked(&inode->i_lock);
309	WARN_ON_ONCE(inode->i_state & I_FREEING);
310
311	inode->i_state &= ~I_SYNC_QUEUED;
312	if (wb != &wb->bdi->wb)
313	list_move(list: &inode->i_io_list, head: &wb->b_attached);
314	else
315	list_del_init(entry: &inode->i_io_list);
316	wb_io_lists_depopulated(wb);
317	}
318
319	/**
320	* locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
321	* @inode: inode of interest with i_lock held
322	*
323	* Returns @inode's wb with its list_lock held. @inode->i_lock must be
324	* held on entry and is released on return. The returned wb is guaranteed
325	* to stay @inode's associated wb until its list_lock is released.
326	*/
327	static struct bdi_writeback *
328	locked_inode_to_wb_and_lock_list(struct inode *inode)
329	__releases(&inode->i_lock)
330	__acquires(&wb->list_lock)
331	{
332	while (true) {
333	struct bdi_writeback *wb = inode_to_wb(inode);
334
335	/*
336	* inode_to_wb() association is protected by both
337	* @inode->i_lock and @wb->list_lock but list_lock nests
338	* outside i_lock. Drop i_lock and verify that the
339	* association hasn't changed after acquiring list_lock.
340	*/
341	wb_get(wb);
342	spin_unlock(lock: &inode->i_lock);
343	spin_lock(lock: &wb->list_lock);
344
345	/* i_wb may have changed inbetween, can't use inode_to_wb() */
346	if (likely(wb == inode->i_wb)) {
347	wb_put(wb); /* @inode already has ref */
348	return wb;
349	}
350
351	spin_unlock(lock: &wb->list_lock);
352	wb_put(wb);
353	cpu_relax();
354	spin_lock(lock: &inode->i_lock);
355	}
356	}
357
358	/**
359	* inode_to_wb_and_lock_list - determine an inode's wb and lock it
360	* @inode: inode of interest
361	*
362	* Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
363	* on entry.
364	*/
365	static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
366	__acquires(&wb->list_lock)
367	{
368	spin_lock(lock: &inode->i_lock);
369	return locked_inode_to_wb_and_lock_list(inode);
370	}
371
372	struct inode_switch_wbs_context {
373	struct rcu_work work;
374
375	/*
376	* Multiple inodes can be switched at once. The switching procedure
377	* consists of two parts, separated by a RCU grace period. To make
378	* sure that the second part is executed for each inode gone through
379	* the first part, all inode pointers are placed into a NULL-terminated
380	* array embedded into struct inode_switch_wbs_context. Otherwise
381	* an inode could be left in a non-consistent state.
382	*/
383	struct bdi_writeback *new_wb;
384	struct inode *inodes[];
385	};
386
387	static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
388	{
389	down_write(sem: &bdi->wb_switch_rwsem);
390	}
391
392	static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
393	{
394	up_write(sem: &bdi->wb_switch_rwsem);
395	}
396
397	static bool inode_do_switch_wbs(struct inode *inode,
398	struct bdi_writeback *old_wb,
399	struct bdi_writeback *new_wb)
400	{
401	struct address_space *mapping = inode->i_mapping;
402	XA_STATE(xas, &mapping->i_pages, 0);
403	struct folio *folio;
404	bool switched = false;
405
406	spin_lock(lock: &inode->i_lock);
407	xa_lock_irq(&mapping->i_pages);
408
409	/*
410	* Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
411	* path owns the inode and we shouldn't modify ->i_io_list.
412	*/
413	if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
414	goto skip_switch;
415
416	trace_inode_switch_wbs(inode, old_wb, new_wb);
417
418	/*
419	* Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
420	* to possibly dirty folios while PAGECACHE_TAG_WRITEBACK points to
421	* folios actually under writeback.
422	*/
423	xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
424	if (folio_test_dirty(folio)) {
425	long nr = folio_nr_pages(folio);
426	wb_stat_mod(wb: old_wb, item: WB_RECLAIMABLE, amount: -nr);
427	wb_stat_mod(wb: new_wb, item: WB_RECLAIMABLE, amount: nr);
428	}
429	}
430
431	xas_set(xas: &xas, index: 0);
432	xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
433	long nr = folio_nr_pages(folio);
434	WARN_ON_ONCE(!folio_test_writeback(folio));
435	wb_stat_mod(wb: old_wb, item: WB_WRITEBACK, amount: -nr);
436	wb_stat_mod(wb: new_wb, item: WB_WRITEBACK, amount: nr);
437	}
438
439	if (mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK)) {
440	atomic_dec(v: &old_wb->writeback_inodes);
441	atomic_inc(v: &new_wb->writeback_inodes);
442	}
443
444	wb_get(wb: new_wb);
445
446	/*
447	* Transfer to @new_wb's IO list if necessary. If the @inode is dirty,
448	* the specific list @inode was on is ignored and the @inode is put on
449	* ->b_dirty which is always correct including from ->b_dirty_time.
450	* The transfer preserves @inode->dirtied_when ordering. If the @inode
451	* was clean, it means it was on the b_attached list, so move it onto
452	* the b_attached list of @new_wb.
453	*/
454	if (!list_empty(head: &inode->i_io_list)) {
455	inode->i_wb = new_wb;
456
457	if (inode->i_state & I_DIRTY_ALL) {
458	struct inode *pos;
459
460	list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
461	if (time_after_eq(inode->dirtied_when,
462	pos->dirtied_when))
463	break;
464	inode_io_list_move_locked(inode, wb: new_wb,
465	head: pos->i_io_list.prev);
466	} else {
467	inode_cgwb_move_to_attached(inode, wb: new_wb);
468	}
469	} else {
470	inode->i_wb = new_wb;
471	}
472
473	/* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
474	inode->i_wb_frn_winner = 0;
475	inode->i_wb_frn_avg_time = 0;
476	inode->i_wb_frn_history = 0;
477	switched = true;
478	skip_switch:
479	/*
480	* Paired with load_acquire in unlocked_inode_to_wb_begin() and
481	* ensures that the new wb is visible if they see !I_WB_SWITCH.
482	*/
483	smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
484
485	xa_unlock_irq(&mapping->i_pages);
486	spin_unlock(lock: &inode->i_lock);
487
488	return switched;
489	}
490
491	static void inode_switch_wbs_work_fn(struct work_struct *work)
492	{
493	struct inode_switch_wbs_context *isw =
494	container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
495	struct backing_dev_info *bdi = inode_to_bdi(inode: isw->inodes[0]);
496	struct bdi_writeback *old_wb = isw->inodes[0]->i_wb;
497	struct bdi_writeback *new_wb = isw->new_wb;
498	unsigned long nr_switched = 0;
499	struct inode **inodep;
500
501	/*
502	* If @inode switches cgwb membership while sync_inodes_sb() is
503	* being issued, sync_inodes_sb() might miss it. Synchronize.
504	*/
505	down_read(sem: &bdi->wb_switch_rwsem);
506
507	/*
508	* By the time control reaches here, RCU grace period has passed
509	* since I_WB_SWITCH assertion and all wb stat update transactions
510	* between unlocked_inode_to_wb_begin/end() are guaranteed to be
511	* synchronizing against the i_pages lock.
512	*
513	* Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
514	* gives us exclusion against all wb related operations on @inode
515	* including IO list manipulations and stat updates.
516	*/
517	if (old_wb < new_wb) {
518	spin_lock(lock: &old_wb->list_lock);
519	spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
520	} else {
521	spin_lock(lock: &new_wb->list_lock);
522	spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
523	}
524
525	for (inodep = isw->inodes; *inodep; inodep++) {
526	WARN_ON_ONCE((*inodep)->i_wb != old_wb);
527	if (inode_do_switch_wbs(inode: *inodep, old_wb, new_wb))
528	nr_switched++;
529	}
530
531	spin_unlock(lock: &new_wb->list_lock);
532	spin_unlock(lock: &old_wb->list_lock);
533
534	up_read(sem: &bdi->wb_switch_rwsem);
535
536	if (nr_switched) {
537	wb_wakeup(wb: new_wb);
538	wb_put_many(wb: old_wb, nr: nr_switched);
539	}
540
541	for (inodep = isw->inodes; *inodep; inodep++)
542	iput(*inodep);
543	wb_put(wb: new_wb);
544	kfree(objp: isw);
545	atomic_dec(v: &isw_nr_in_flight);
546	}
547
548	static bool inode_prepare_wbs_switch(struct inode *inode,
549	struct bdi_writeback *new_wb)
550	{
551	/*
552	* Paired with smp_mb() in cgroup_writeback_umount().
553	* isw_nr_in_flight must be increased before checking SB_ACTIVE and
554	* grabbing an inode, otherwise isw_nr_in_flight can be observed as 0
555	* in cgroup_writeback_umount() and the isw_wq will be not flushed.
556	*/
557	smp_mb();
558
559	if (IS_DAX(inode))
560	return false;
561
562	/* while holding I_WB_SWITCH, no one else can update the association */
563	spin_lock(lock: &inode->i_lock);
564	if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
565	inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
566	inode_to_wb(inode) == new_wb) {
567	spin_unlock(lock: &inode->i_lock);
568	return false;
569	}
570	inode->i_state |= I_WB_SWITCH;
571	__iget(inode);
572	spin_unlock(lock: &inode->i_lock);
573
574	return true;
575	}
576
577	/**
578	* inode_switch_wbs - change the wb association of an inode
579	* @inode: target inode
580	* @new_wb_id: ID of the new wb
581	*
582	* Switch @inode's wb association to the wb identified by @new_wb_id. The
583	* switching is performed asynchronously and may fail silently.
584	*/
585	static void inode_switch_wbs(struct inode *inode, int new_wb_id)
586	{
587	struct backing_dev_info *bdi = inode_to_bdi(inode);
588	struct cgroup_subsys_state *memcg_css;
589	struct inode_switch_wbs_context *isw;
590
591	/* noop if seems to be already in progress */
592	if (inode->i_state & I_WB_SWITCH)
593	return;
594
595	/* avoid queueing a new switch if too many are already in flight */
596	if (atomic_read(v: &isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
597	return;
598
599	isw = kzalloc(struct_size(isw, inodes, 2), GFP_ATOMIC);
600	if (!isw)
601	return;
602
603	atomic_inc(v: &isw_nr_in_flight);
604
605	/* find and pin the new wb */
606	rcu_read_lock();
607	memcg_css = css_from_id(id: new_wb_id, ss: &memory_cgrp_subsys);
608	if (memcg_css && !css_tryget(css: memcg_css))
609	memcg_css = NULL;
610	rcu_read_unlock();
611	if (!memcg_css)
612	goto out_free;
613
614	isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
615	css_put(css: memcg_css);
616	if (!isw->new_wb)
617	goto out_free;
618
619	if (!inode_prepare_wbs_switch(inode, new_wb: isw->new_wb))
620	goto out_free;
621
622	isw->inodes[0] = inode;
623
624	/*
625	* In addition to synchronizing among switchers, I_WB_SWITCH tells
626	* the RCU protected stat update paths to grab the i_page
627	* lock so that stat transfer can synchronize against them.
628	* Let's continue after I_WB_SWITCH is guaranteed to be visible.
629	*/
630	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
631	queue_rcu_work(wq: isw_wq, rwork: &isw->work);
632	return;
633
634	out_free:
635	atomic_dec(v: &isw_nr_in_flight);
636	if (isw->new_wb)
637	wb_put(wb: isw->new_wb);
638	kfree(objp: isw);
639	}
640
641	static bool isw_prepare_wbs_switch(struct inode_switch_wbs_context *isw,
642	struct list_head *list, int *nr)
643	{
644	struct inode *inode;
645
646	list_for_each_entry(inode, list, i_io_list) {
647	if (!inode_prepare_wbs_switch(inode, new_wb: isw->new_wb))
648	continue;
649
650	isw->inodes[*nr] = inode;
651	(*nr)++;
652
653	if (*nr >= WB_MAX_INODES_PER_ISW - 1)
654	return true;
655	}
656	return false;
657	}
658
659	/**
660	* cleanup_offline_cgwb - detach associated inodes
661	* @wb: target wb
662	*
663	* Switch all inodes attached to @wb to a nearest living ancestor's wb in order
664	* to eventually release the dying @wb. Returns %true if not all inodes were
665	* switched and the function has to be restarted.
666	*/
667	bool cleanup_offline_cgwb(struct bdi_writeback *wb)
668	{
669	struct cgroup_subsys_state *memcg_css;
670	struct inode_switch_wbs_context *isw;
671	int nr;
672	bool restart = false;
673
674	isw = kzalloc(struct_size(isw, inodes, WB_MAX_INODES_PER_ISW),
675	GFP_KERNEL);
676	if (!isw)
677	return restart;
678
679	atomic_inc(v: &isw_nr_in_flight);
680
681	for (memcg_css = wb->memcg_css->parent; memcg_css;
682	memcg_css = memcg_css->parent) {
683	isw->new_wb = wb_get_create(bdi: wb->bdi, memcg_css, GFP_KERNEL);
684	if (isw->new_wb)
685	break;
686	}
687	if (unlikely(!isw->new_wb))
688	isw->new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
689
690	nr = 0;
691	spin_lock(lock: &wb->list_lock);
692	/*
693	* In addition to the inodes that have completed writeback, also switch
694	* cgwbs for those inodes only with dirty timestamps. Otherwise, those
695	* inodes won't be written back for a long time when lazytime is
696	* enabled, and thus pinning the dying cgwbs. It won't break the
697	* bandwidth restrictions, as writeback of inode metadata is not
698	* accounted for.
699	*/
700	restart = isw_prepare_wbs_switch(isw, list: &wb->b_attached, nr: &nr);
701	if (!restart)
702	restart = isw_prepare_wbs_switch(isw, list: &wb->b_dirty_time, nr: &nr);
703	spin_unlock(lock: &wb->list_lock);
704
705	/* no attached inodes? bail out */
706	if (nr == 0) {
707	atomic_dec(v: &isw_nr_in_flight);
708	wb_put(wb: isw->new_wb);
709	kfree(objp: isw);
710	return restart;
711	}
712
713	/*
714	* In addition to synchronizing among switchers, I_WB_SWITCH tells
715	* the RCU protected stat update paths to grab the i_page
716	* lock so that stat transfer can synchronize against them.
717	* Let's continue after I_WB_SWITCH is guaranteed to be visible.
718	*/
719	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
720	queue_rcu_work(wq: isw_wq, rwork: &isw->work);
721
722	return restart;
723	}
724
725	/**
726	* wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
727	* @wbc: writeback_control of interest
728	* @inode: target inode
729	*
730	* @inode is locked and about to be written back under the control of @wbc.
731	* Record @inode's writeback context into @wbc and unlock the i_lock. On
732	* writeback completion, wbc_detach_inode() should be called. This is used
733	* to track the cgroup writeback context.
734	*/
735	void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
736	struct inode *inode)
737	{
738	if (!inode_cgwb_enabled(inode)) {
739	spin_unlock(lock: &inode->i_lock);
740	return;
741	}
742
743	wbc->wb = inode_to_wb(inode);
744	wbc->inode = inode;
745
746	wbc->wb_id = wbc->wb->memcg_css->id;
747	wbc->wb_lcand_id = inode->i_wb_frn_winner;
748	wbc->wb_tcand_id = 0;
749	wbc->wb_bytes = 0;
750	wbc->wb_lcand_bytes = 0;
751	wbc->wb_tcand_bytes = 0;
752
753	wb_get(wb: wbc->wb);
754	spin_unlock(lock: &inode->i_lock);
755
756	/*
757	* A dying wb indicates that either the blkcg associated with the
758	* memcg changed or the associated memcg is dying. In the first
759	* case, a replacement wb should already be available and we should
760	* refresh the wb immediately. In the second case, trying to
761	* refresh will keep failing.
762	*/
763	if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
764	inode_switch_wbs(inode, new_wb_id: wbc->wb_id);
765	}
766	EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
767
768	/**
769	* wbc_detach_inode - disassociate wbc from inode and perform foreign detection
770	* @wbc: writeback_control of the just finished writeback
771	*
772	* To be called after a writeback attempt of an inode finishes and undoes
773	* wbc_attach_and_unlock_inode(). Can be called under any context.
774	*
775	* As concurrent write sharing of an inode is expected to be very rare and
776	* memcg only tracks page ownership on first-use basis severely confining
777	* the usefulness of such sharing, cgroup writeback tracks ownership
778	* per-inode. While the support for concurrent write sharing of an inode
779	* is deemed unnecessary, an inode being written to by different cgroups at
780	* different points in time is a lot more common, and, more importantly,
781	* charging only by first-use can too readily lead to grossly incorrect
782	* behaviors (single foreign page can lead to gigabytes of writeback to be
783	* incorrectly attributed).
784	*
785	* To resolve this issue, cgroup writeback detects the majority dirtier of
786	* an inode and transfers the ownership to it. To avoid unnecessary
787	* oscillation, the detection mechanism keeps track of history and gives
788	* out the switch verdict only if the foreign usage pattern is stable over
789	* a certain amount of time and/or writeback attempts.
790	*
791	* On each writeback attempt, @wbc tries to detect the majority writer
792	* using Boyer-Moore majority vote algorithm. In addition to the byte
793	* count from the majority voting, it also counts the bytes written for the
794	* current wb and the last round's winner wb (max of last round's current
795	* wb, the winner from two rounds ago, and the last round's majority
796	* candidate). Keeping track of the historical winner helps the algorithm
797	* to semi-reliably detect the most active writer even when it's not the
798	* absolute majority.
799	*
800	* Once the winner of the round is determined, whether the winner is
801	* foreign or not and how much IO time the round consumed is recorded in
802	* inode->i_wb_frn_history. If the amount of recorded foreign IO time is
803	* over a certain threshold, the switch verdict is given.
804	*/
805	void wbc_detach_inode(struct writeback_control *wbc)
806	{
807	struct bdi_writeback *wb = wbc->wb;
808	struct inode *inode = wbc->inode;
809	unsigned long avg_time, max_bytes, max_time;
810	u16 history;
811	int max_id;
812
813	if (!wb)
814	return;
815
816	history = inode->i_wb_frn_history;
817	avg_time = inode->i_wb_frn_avg_time;
818
819	/* pick the winner of this round */
820	if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
821	wbc->wb_bytes >= wbc->wb_tcand_bytes) {
822	max_id = wbc->wb_id;
823	max_bytes = wbc->wb_bytes;
824	} else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
825	max_id = wbc->wb_lcand_id;
826	max_bytes = wbc->wb_lcand_bytes;
827	} else {
828	max_id = wbc->wb_tcand_id;
829	max_bytes = wbc->wb_tcand_bytes;
830	}
831
832	/*
833	* Calculate the amount of IO time the winner consumed and fold it
834	* into the running average kept per inode. If the consumed IO
835	* time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
836	* deciding whether to switch or not. This is to prevent one-off
837	* small dirtiers from skewing the verdict.
838	*/
839	max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
840	wb->avg_write_bandwidth);
841	if (avg_time)
842	avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
843	(avg_time >> WB_FRN_TIME_AVG_SHIFT);
844	else
845	avg_time = max_time; /* immediate catch up on first run */
846
847	if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
848	int slots;
849
850	/*
851	* The switch verdict is reached if foreign wb's consume
852	* more than a certain proportion of IO time in a
853	* WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
854	* history mask where each bit represents one sixteenth of
855	* the period. Determine the number of slots to shift into
856	* history from @max_time.
857	*/
858	slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
859	(unsigned long)WB_FRN_HIST_MAX_SLOTS);
860	history <<= slots;
861	if (wbc->wb_id != max_id)
862	history |= (1U << slots) - 1;
863
864	if (history)
865	trace_inode_foreign_history(inode, wbc, history);
866
867	/*
868	* Switch if the current wb isn't the consistent winner.
869	* If there are multiple closely competing dirtiers, the
870	* inode may switch across them repeatedly over time, which
871	* is okay. The main goal is avoiding keeping an inode on
872	* the wrong wb for an extended period of time.
873	*/
874	if (hweight16(history) > WB_FRN_HIST_THR_SLOTS)
875	inode_switch_wbs(inode, new_wb_id: max_id);
876	}
877
878	/*
879	* Multiple instances of this function may race to update the
880	* following fields but we don't mind occassional inaccuracies.
881	*/
882	inode->i_wb_frn_winner = max_id;
883	inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
884	inode->i_wb_frn_history = history;
885
886	wb_put(wb: wbc->wb);
887	wbc->wb = NULL;
888	}
889	EXPORT_SYMBOL_GPL(wbc_detach_inode);
890
891	/**
892	* wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
893	* @wbc: writeback_control of the writeback in progress
894	* @page: page being written out
895	* @bytes: number of bytes being written out
896	*
897	* @bytes from @page are about to written out during the writeback
898	* controlled by @wbc. Keep the book for foreign inode detection. See
899	* wbc_detach_inode().
900	*/
901	void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
902	size_t bytes)
903	{
904	struct folio *folio;
905	struct cgroup_subsys_state *css;
906	int id;
907
908	/*
909	* pageout() path doesn't attach @wbc to the inode being written
910	* out. This is intentional as we don't want the function to block
911	* behind a slow cgroup. Ultimately, we want pageout() to kick off
912	* regular writeback instead of writing things out itself.
913	*/
914	if (!wbc->wb || wbc->no_cgroup_owner)
915	return;
916
917	folio = page_folio(page);
918	css = mem_cgroup_css_from_folio(folio);
919	/* dead cgroups shouldn't contribute to inode ownership arbitration */
920	if (!(css->flags & CSS_ONLINE))
921	return;
922
923	id = css->id;
924
925	if (id == wbc->wb_id) {
926	wbc->wb_bytes += bytes;
927	return;
928	}
929
930	if (id == wbc->wb_lcand_id)
931	wbc->wb_lcand_bytes += bytes;
932
933	/* Boyer-Moore majority vote algorithm */
934	if (!wbc->wb_tcand_bytes)
935	wbc->wb_tcand_id = id;
936	if (id == wbc->wb_tcand_id)
937	wbc->wb_tcand_bytes += bytes;
938	else
939	wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
940	}
941	EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
942
943	/**
944	* wb_split_bdi_pages - split nr_pages to write according to bandwidth
945	* @wb: target bdi_writeback to split @nr_pages to
946	* @nr_pages: number of pages to write for the whole bdi
947	*
948	* Split @wb's portion of @nr_pages according to @wb's write bandwidth in
949	* relation to the total write bandwidth of all wb's w/ dirty inodes on
950	* @wb->bdi.
951	*/
952	static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
953	{
954	unsigned long this_bw = wb->avg_write_bandwidth;
955	unsigned long tot_bw = atomic_long_read(v: &wb->bdi->tot_write_bandwidth);
956
957	if (nr_pages == LONG_MAX)
958	return LONG_MAX;
959
960	/*
961	* This may be called on clean wb's and proportional distribution
962	* may not make sense, just use the original @nr_pages in those
963	* cases. In general, we wanna err on the side of writing more.
964	*/
965	if (!tot_bw || this_bw >= tot_bw)
966	return nr_pages;
967	else
968	return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
969	}
970
971	/**
972	* bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
973	* @bdi: target backing_dev_info
974	* @base_work: wb_writeback_work to issue
975	* @skip_if_busy: skip wb's which already have writeback in progress
976	*
977	* Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
978	* have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
979	* distributed to the busy wbs according to each wb's proportion in the
980	* total active write bandwidth of @bdi.
981	*/
982	static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
983	struct wb_writeback_work *base_work,
984	bool skip_if_busy)
985	{
986	struct bdi_writeback *last_wb = NULL;
987	struct bdi_writeback *wb = list_entry(&bdi->wb_list,
988	struct bdi_writeback, bdi_node);
989
990	might_sleep();
991	restart:
992	rcu_read_lock();
993	list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
994	DEFINE_WB_COMPLETION(fallback_work_done, bdi);
995	struct wb_writeback_work fallback_work;
996	struct wb_writeback_work *work;
997	long nr_pages;
998
999	if (last_wb) {
1000	wb_put(wb: last_wb);
1001	last_wb = NULL;
1002	}
1003
1004	/* SYNC_ALL writes out I_DIRTY_TIME too */
1005	if (!wb_has_dirty_io(wb) &&
1006	(base_work->sync_mode == WB_SYNC_NONE ||
1007	list_empty(head: &wb->b_dirty_time)))
1008	continue;
1009	if (skip_if_busy && writeback_in_progress(wb))
1010	continue;
1011
1012	nr_pages = wb_split_bdi_pages(wb, nr_pages: base_work->nr_pages);
1013
1014	work = kmalloc(size: sizeof(*work), GFP_ATOMIC);
1015	if (work) {
1016	*work = *base_work;
1017	work->nr_pages = nr_pages;
1018	work->auto_free = 1;
1019	wb_queue_work(wb, work);
1020	continue;
1021	}
1022
1023	/*
1024	* If wb_tryget fails, the wb has been shutdown, skip it.
1025	*
1026	* Pin @wb so that it stays on @bdi->wb_list. This allows
1027	* continuing iteration from @wb after dropping and
1028	* regrabbing rcu read lock.
1029	*/
1030	if (!wb_tryget(wb))
1031	continue;
1032
1033	/* alloc failed, execute synchronously using on-stack fallback */
1034	work = &fallback_work;
1035	*work = *base_work;
1036	work->nr_pages = nr_pages;
1037	work->auto_free = 0;
1038	work->done = &fallback_work_done;
1039
1040	wb_queue_work(wb, work);
1041	last_wb = wb;
1042
1043	rcu_read_unlock();
1044	wb_wait_for_completion(done: &fallback_work_done);
1045	goto restart;
1046	}
1047	rcu_read_unlock();
1048
1049	if (last_wb)
1050	wb_put(wb: last_wb);
1051	}
1052
1053	/**
1054	* cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
1055	* @bdi_id: target bdi id
1056	* @memcg_id: target memcg css id
1057	* @reason: reason why some writeback work initiated
1058	* @done: target wb_completion
1059	*
1060	* Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
1061	* with the specified parameters.
1062	*/
1063	int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,
1064	enum wb_reason reason, struct wb_completion *done)
1065	{
1066	struct backing_dev_info *bdi;
1067	struct cgroup_subsys_state *memcg_css;
1068	struct bdi_writeback *wb;
1069	struct wb_writeback_work *work;
1070	unsigned long dirty;
1071	int ret;
1072
1073	/* lookup bdi and memcg */
1074	bdi = bdi_get_by_id(id: bdi_id);
1075	if (!bdi)
1076	return -ENOENT;
1077
1078	rcu_read_lock();
1079	memcg_css = css_from_id(id: memcg_id, ss: &memory_cgrp_subsys);
1080	if (memcg_css && !css_tryget(css: memcg_css))
1081	memcg_css = NULL;
1082	rcu_read_unlock();
1083	if (!memcg_css) {
1084	ret = -ENOENT;
1085	goto out_bdi_put;
1086	}
1087
1088	/*
1089	* And find the associated wb. If the wb isn't there already
1090	* there's nothing to flush, don't create one.
1091	*/
1092	wb = wb_get_lookup(bdi, memcg_css);
1093	if (!wb) {
1094	ret = -ENOENT;
1095	goto out_css_put;
1096	}
1097
1098	/*
1099	* The caller is attempting to write out most of
1100	* the currently dirty pages. Let's take the current dirty page
1101	* count and inflate it by 25% which should be large enough to
1102	* flush out most dirty pages while avoiding getting livelocked by
1103	* concurrent dirtiers.
1104	*
1105	* BTW the memcg stats are flushed periodically and this is best-effort
1106	* estimation, so some potential error is ok.
1107	*/
1108	dirty = memcg_page_state(memcg: mem_cgroup_from_css(css: memcg_css), idx: NR_FILE_DIRTY);
1109	dirty = dirty * 10 / 8;
1110
1111	/* issue the writeback work */
1112	work = kzalloc(size: sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
1113	if (work) {
1114	work->nr_pages = dirty;
1115	work->sync_mode = WB_SYNC_NONE;
1116	work->range_cyclic = 1;
1117	work->reason = reason;
1118	work->done = done;
1119	work->auto_free = 1;
1120	wb_queue_work(wb, work);
1121	ret = 0;
1122	} else {
1123	ret = -ENOMEM;
1124	}
1125
1126	wb_put(wb);
1127	out_css_put:
1128	css_put(css: memcg_css);
1129	out_bdi_put:
1130	bdi_put(bdi);
1131	return ret;
1132	}
1133
1134	/**
1135	* cgroup_writeback_umount - flush inode wb switches for umount
1136	*
1137	* This function is called when a super_block is about to be destroyed and
1138	* flushes in-flight inode wb switches. An inode wb switch goes through
1139	* RCU and then workqueue, so the two need to be flushed in order to ensure
1140	* that all previously scheduled switches are finished. As wb switches are
1141	* rare occurrences and synchronize_rcu() can take a while, perform
1142	* flushing iff wb switches are in flight.
1143	*/
1144	void cgroup_writeback_umount(void)
1145	{
1146	/*
1147	* SB_ACTIVE should be reliably cleared before checking
1148	* isw_nr_in_flight, see generic_shutdown_super().
1149	*/
1150	smp_mb();
1151
1152	if (atomic_read(v: &isw_nr_in_flight)) {
1153	/*
1154	* Use rcu_barrier() to wait for all pending callbacks to
1155	* ensure that all in-flight wb switches are in the workqueue.
1156	*/
1157	rcu_barrier();
1158	flush_workqueue(isw_wq);
1159	}
1160	}
1161
1162	static int __init cgroup_writeback_init(void)
1163	{
1164	isw_wq = alloc_workqueue(fmt: "inode_switch_wbs", flags: 0, max_active: 0);
1165	if (!isw_wq)
1166	return -ENOMEM;
1167	return 0;
1168	}
1169	fs_initcall(cgroup_writeback_init);
1170
1171	#else /* CONFIG_CGROUP_WRITEBACK */
1172
1173	static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1174	static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1175
1176	static void inode_cgwb_move_to_attached(struct inode *inode,
1177	struct bdi_writeback *wb)
1178	{
1179	assert_spin_locked(&wb->list_lock);
1180	assert_spin_locked(&inode->i_lock);
1181	WARN_ON_ONCE(inode->i_state & I_FREEING);
1182
1183	inode->i_state &= ~I_SYNC_QUEUED;
1184	list_del_init(&inode->i_io_list);
1185	wb_io_lists_depopulated(wb);
1186	}
1187
1188	static struct bdi_writeback *
1189	locked_inode_to_wb_and_lock_list(struct inode *inode)
1190	__releases(&inode->i_lock)
1191	__acquires(&wb->list_lock)
1192	{
1193	struct bdi_writeback *wb = inode_to_wb(inode);
1194
1195	spin_unlock(&inode->i_lock);
1196	spin_lock(&wb->list_lock);
1197	return wb;
1198	}
1199
1200	static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
1201	__acquires(&wb->list_lock)
1202	{
1203	struct bdi_writeback *wb = inode_to_wb(inode);
1204
1205	spin_lock(&wb->list_lock);
1206	return wb;
1207	}
1208
1209	static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
1210	{
1211	return nr_pages;
1212	}
1213
1214	static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
1215	struct wb_writeback_work *base_work,
1216	bool skip_if_busy)
1217	{
1218	might_sleep();
1219
1220	if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
1221	base_work->auto_free = 0;
1222	wb_queue_work(&bdi->wb, base_work);
1223	}
1224	}
1225
1226	#endif /* CONFIG_CGROUP_WRITEBACK */
1227
1228	/*
1229	* Add in the number of potentially dirty inodes, because each inode
1230	* write can dirty pagecache in the underlying blockdev.
1231	*/
1232	static unsigned long get_nr_dirty_pages(void)
1233	{
1234	return global_node_page_state(item: NR_FILE_DIRTY) +
1235	get_nr_dirty_inodes();
1236	}
1237
1238	static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
1239	{
1240	if (!wb_has_dirty_io(wb))
1241	return;
1242
1243	/*
1244	* All callers of this function want to start writeback of all
1245	* dirty pages. Places like vmscan can call this at a very
1246	* high frequency, causing pointless allocations of tons of
1247	* work items and keeping the flusher threads busy retrieving
1248	* that work. Ensure that we only allow one of them pending and
1249	* inflight at the time.
1250	*/
1251	if (test_bit(WB_start_all, &wb->state) ||
1252	test_and_set_bit(nr: WB_start_all, addr: &wb->state))
1253	return;
1254
1255	wb->start_all_reason = reason;
1256	wb_wakeup(wb);
1257	}
1258
1259	/**
1260	* wb_start_background_writeback - start background writeback
1261	* @wb: bdi_writback to write from
1262	*
1263	* Description:
1264	* This makes sure WB_SYNC_NONE background writeback happens. When
1265	* this function returns, it is only guaranteed that for given wb
1266	* some IO is happening if we are over background dirty threshold.
1267	* Caller need not hold sb s_umount semaphore.
1268	*/
1269	void wb_start_background_writeback(struct bdi_writeback *wb)
1270	{
1271	/*
1272	* We just wake up the flusher thread. It will perform background
1273	* writeback as soon as there is no other work to do.
1274	*/
1275	trace_writeback_wake_background(wb);
1276	wb_wakeup(wb);
1277	}
1278
1279	/*
1280	* Remove the inode from the writeback list it is on.
1281	*/
1282	void inode_io_list_del(struct inode *inode)
1283	{
1284	struct bdi_writeback *wb;
1285
1286	wb = inode_to_wb_and_lock_list(inode);
1287	spin_lock(lock: &inode->i_lock);
1288
1289	inode->i_state &= ~I_SYNC_QUEUED;
1290	list_del_init(entry: &inode->i_io_list);
1291	wb_io_lists_depopulated(wb);
1292
1293	spin_unlock(lock: &inode->i_lock);
1294	spin_unlock(lock: &wb->list_lock);
1295	}
1296	EXPORT_SYMBOL(inode_io_list_del);
1297
1298	/*
1299	* mark an inode as under writeback on the sb
1300	*/
1301	void sb_mark_inode_writeback(struct inode *inode)
1302	{
1303	struct super_block *sb = inode->i_sb;
1304	unsigned long flags;
1305
1306	if (list_empty(head: &inode->i_wb_list)) {
1307	spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1308	if (list_empty(head: &inode->i_wb_list)) {
1309	list_add_tail(new: &inode->i_wb_list, head: &sb->s_inodes_wb);
1310	trace_sb_mark_inode_writeback(inode);
1311	}
1312	spin_unlock_irqrestore(lock: &sb->s_inode_wblist_lock, flags);
1313	}
1314	}
1315
1316	/*
1317	* clear an inode as under writeback on the sb
1318	*/
1319	void sb_clear_inode_writeback(struct inode *inode)
1320	{
1321	struct super_block *sb = inode->i_sb;
1322	unsigned long flags;
1323
1324	if (!list_empty(head: &inode->i_wb_list)) {
1325	spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1326	if (!list_empty(head: &inode->i_wb_list)) {
1327	list_del_init(entry: &inode->i_wb_list);
1328	trace_sb_clear_inode_writeback(inode);
1329	}
1330	spin_unlock_irqrestore(lock: &sb->s_inode_wblist_lock, flags);
1331	}
1332	}
1333
1334	/*
1335	* Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1336	* furthest end of its superblock's dirty-inode list.
1337	*
1338	* Before stamping the inode's ->dirtied_when, we check to see whether it is
1339	* already the most-recently-dirtied inode on the b_dirty list. If that is
1340	* the case then the inode must have been redirtied while it was being written
1341	* out and we don't reset its dirtied_when.
1342	*/
1343	static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
1344	{
1345	assert_spin_locked(&inode->i_lock);
1346
1347	inode->i_state &= ~I_SYNC_QUEUED;
1348	/*
1349	* When the inode is being freed just don't bother with dirty list
1350	* tracking. Flush worker will ignore this inode anyway and it will
1351	* trigger assertions in inode_io_list_move_locked().
1352	*/
1353	if (inode->i_state & I_FREEING) {
1354	list_del_init(entry: &inode->i_io_list);
1355	wb_io_lists_depopulated(wb);
1356	return;
1357	}
1358	if (!list_empty(head: &wb->b_dirty)) {
1359	struct inode *tail;
1360
1361	tail = wb_inode(head: wb->b_dirty.next);
1362	if (time_before(inode->dirtied_when, tail->dirtied_when))
1363	inode->dirtied_when = jiffies;
1364	}
1365	inode_io_list_move_locked(inode, wb, head: &wb->b_dirty);
1366	}
1367
1368	static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
1369	{
1370	spin_lock(lock: &inode->i_lock);
1371	redirty_tail_locked(inode, wb);
1372	spin_unlock(lock: &inode->i_lock);
1373	}
1374
1375	/*
1376	* requeue inode for re-scanning after bdi->b_io list is exhausted.
1377	*/
1378	static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
1379	{
1380	inode_io_list_move_locked(inode, wb, head: &wb->b_more_io);
1381	}
1382
1383	static void inode_sync_complete(struct inode *inode)
1384	{
1385	inode->i_state &= ~I_SYNC;
1386	/* If inode is clean an unused, put it into LRU now... */
1387	inode_add_lru(inode);
1388	/* Waiters must see I_SYNC cleared before being woken up */
1389	smp_mb();
1390	wake_up_bit(word: &inode->i_state, __I_SYNC);
1391	}
1392
1393	static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1394	{
1395	bool ret = time_after(inode->dirtied_when, t);
1396	#ifndef CONFIG_64BIT
1397	/*
1398	* For inodes being constantly redirtied, dirtied_when can get stuck.
1399	* It _appears_ to be in the future, but is actually in distant past.
1400	* This test is necessary to prevent such wrapped-around relative times
1401	* from permanently stopping the whole bdi writeback.
1402	*/
1403	ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1404	#endif
1405	return ret;
1406	}
1407
1408	/*
1409	* Move expired (dirtied before dirtied_before) dirty inodes from
1410	* @delaying_queue to @dispatch_queue.
1411	*/
1412	static int move_expired_inodes(struct list_head *delaying_queue,
1413	struct list_head *dispatch_queue,
1414	unsigned long dirtied_before)
1415	{
1416	LIST_HEAD(tmp);
1417	struct list_head *pos, *node;
1418	struct super_block *sb = NULL;
1419	struct inode *inode;
1420	int do_sb_sort = 0;
1421	int moved = 0;
1422
1423	while (!list_empty(head: delaying_queue)) {
1424	inode = wb_inode(head: delaying_queue->prev);
1425	if (inode_dirtied_after(inode, t: dirtied_before))
1426	break;
1427	spin_lock(lock: &inode->i_lock);
1428	list_move(list: &inode->i_io_list, head: &tmp);
1429	moved++;
1430	inode->i_state |= I_SYNC_QUEUED;
1431	spin_unlock(lock: &inode->i_lock);
1432	if (sb_is_blkdev_sb(sb: inode->i_sb))
1433	continue;
1434	if (sb && sb != inode->i_sb)
1435	do_sb_sort = 1;
1436	sb = inode->i_sb;
1437	}
1438
1439	/* just one sb in list, splice to dispatch_queue and we're done */
1440	if (!do_sb_sort) {
1441	list_splice(list: &tmp, head: dispatch_queue);
1442	goto out;
1443	}
1444
1445	/*
1446	* Although inode's i_io_list is moved from 'tmp' to 'dispatch_queue',
1447	* we don't take inode->i_lock here because it is just a pointless overhead.
1448	* Inode is already marked as I_SYNC_QUEUED so writeback list handling is
1449	* fully under our control.
1450	*/
1451	while (!list_empty(head: &tmp)) {
1452	sb = wb_inode(head: tmp.prev)->i_sb;
1453	list_for_each_prev_safe(pos, node, &tmp) {
1454	inode = wb_inode(head: pos);
1455	if (inode->i_sb == sb)
1456	list_move(list: &inode->i_io_list, head: dispatch_queue);
1457	}
1458	}
1459	out:
1460	return moved;
1461	}
1462
1463	/*
1464	* Queue all expired dirty inodes for io, eldest first.
1465	* Before
1466	* newly dirtied b_dirty b_io b_more_io
1467	* =============> gf edc BA
1468	* After
1469	* newly dirtied b_dirty b_io b_more_io
1470	* =============> g fBAedc
1471	* |
1472	* +--> dequeue for IO
1473	*/
1474	static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
1475	unsigned long dirtied_before)
1476	{
1477	int moved;
1478	unsigned long time_expire_jif = dirtied_before;
1479
1480	assert_spin_locked(&wb->list_lock);
1481	list_splice_init(list: &wb->b_more_io, head: &wb->b_io);
1482	moved = move_expired_inodes(delaying_queue: &wb->b_dirty, dispatch_queue: &wb->b_io, dirtied_before);
1483	if (!work->for_sync)
1484	time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
1485	moved += move_expired_inodes(delaying_queue: &wb->b_dirty_time, dispatch_queue: &wb->b_io,
1486	dirtied_before: time_expire_jif);
1487	if (moved)
1488	wb_io_lists_populated(wb);
1489	trace_writeback_queue_io(wb, work, dirtied_before, moved);
1490	}
1491
1492	static int write_inode(struct inode *inode, struct writeback_control *wbc)
1493	{
1494	int ret;
1495
1496	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1497	trace_writeback_write_inode_start(inode, wbc);
1498	ret = inode->i_sb->s_op->write_inode(inode, wbc);
1499	trace_writeback_write_inode(inode, wbc);
1500	return ret;
1501	}
1502	return 0;
1503	}
1504
1505	/*
1506	* Wait for writeback on an inode to complete. Called with i_lock held.
1507	* Caller must make sure inode cannot go away when we drop i_lock.
1508	*/
1509	static void __inode_wait_for_writeback(struct inode *inode)
1510	__releases(inode->i_lock)
1511	__acquires(inode->i_lock)
1512	{
1513	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1514	wait_queue_head_t *wqh;
1515
1516	wqh = bit_waitqueue(word: &inode->i_state, __I_SYNC);
1517	while (inode->i_state & I_SYNC) {
1518	spin_unlock(lock: &inode->i_lock);
1519	__wait_on_bit(wq_head: wqh, wbq_entry: &wq, action: bit_wait,
1520	TASK_UNINTERRUPTIBLE);
1521	spin_lock(lock: &inode->i_lock);
1522	}
1523	}
1524
1525	/*
1526	* Wait for writeback on an inode to complete. Caller must have inode pinned.
1527	*/
1528	void inode_wait_for_writeback(struct inode *inode)
1529	{
1530	spin_lock(lock: &inode->i_lock);
1531	__inode_wait_for_writeback(inode);
1532	spin_unlock(lock: &inode->i_lock);
1533	}
1534
1535	/*
1536	* Sleep until I_SYNC is cleared. This function must be called with i_lock
1537	* held and drops it. It is aimed for callers not holding any inode reference
1538	* so once i_lock is dropped, inode can go away.
1539	*/
1540	static void inode_sleep_on_writeback(struct inode *inode)
1541	__releases(inode->i_lock)
1542	{
1543	DEFINE_WAIT(wait);
1544	wait_queue_head_t *wqh = bit_waitqueue(word: &inode->i_state, __I_SYNC);
1545	int sleep;
1546
1547	prepare_to_wait(wq_head: wqh, wq_entry: &wait, TASK_UNINTERRUPTIBLE);
1548	sleep = inode->i_state & I_SYNC;
1549	spin_unlock(lock: &inode->i_lock);
1550	if (sleep)
1551	schedule();
1552	finish_wait(wq_head: wqh, wq_entry: &wait);
1553	}
1554
1555	/*
1556	* Find proper writeback list for the inode depending on its current state and
1557	* possibly also change of its state while we were doing writeback. Here we
1558	* handle things such as livelock prevention or fairness of writeback among
1559	* inodes. This function can be called only by flusher thread - noone else
1560	* processes all inodes in writeback lists and requeueing inodes behind flusher
1561	* thread's back can have unexpected consequences.
1562	*/
1563	static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1564	struct writeback_control *wbc)
1565	{
1566	if (inode->i_state & I_FREEING)
1567	return;
1568
1569	/*
1570	* Sync livelock prevention. Each inode is tagged and synced in one
1571	* shot. If still dirty, it will be redirty_tail()'ed below. Update
1572	* the dirty time to prevent enqueue and sync it again.
1573	*/
1574	if ((inode->i_state & I_DIRTY) &&
1575	(wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1576	inode->dirtied_when = jiffies;
1577
1578	if (wbc->pages_skipped) {
1579	/*
1580	* Writeback is not making progress due to locked buffers.
1581	* Skip this inode for now. Although having skipped pages
1582	* is odd for clean inodes, it can happen for some
1583	* filesystems so handle that gracefully.
1584	*/
1585	if (inode->i_state & I_DIRTY_ALL)
1586	redirty_tail_locked(inode, wb);
1587	else
1588	inode_cgwb_move_to_attached(inode, wb);
1589	return;
1590	}
1591
1592	if (mapping_tagged(mapping: inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1593	/*
1594	* We didn't write back all the pages. nfs_writepages()
1595	* sometimes bales out without doing anything.
1596	*/
1597	if (wbc->nr_to_write <= 0) {
1598	/* Slice used up. Queue for next turn. */
1599	requeue_io(inode, wb);
1600	} else {
1601	/*
1602	* Writeback blocked by something other than
1603	* congestion. Delay the inode for some time to
1604	* avoid spinning on the CPU (100% iowait)
1605	* retrying writeback of the dirty page/inode
1606	* that cannot be performed immediately.
1607	*/
1608	redirty_tail_locked(inode, wb);
1609	}
1610	} else if (inode->i_state & I_DIRTY) {
1611	/*
1612	* Filesystems can dirty the inode during writeback operations,
1613	* such as delayed allocation during submission or metadata
1614	* updates after data IO completion.
1615	*/
1616	redirty_tail_locked(inode, wb);
1617	} else if (inode->i_state & I_DIRTY_TIME) {
1618	inode->dirtied_when = jiffies;
1619	inode_io_list_move_locked(inode, wb, head: &wb->b_dirty_time);
1620	inode->i_state &= ~I_SYNC_QUEUED;
1621	} else {
1622	/* The inode is clean. Remove from writeback lists. */
1623	inode_cgwb_move_to_attached(inode, wb);
1624	}
1625	}
1626
1627	/*
1628	* Write out an inode and its dirty pages (or some of its dirty pages, depending
1629	* on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
1630	*
1631	* This doesn't remove the inode from the writeback list it is on, except
1632	* potentially to move it from b_dirty_time to b_dirty due to timestamp
1633	* expiration. The caller is otherwise responsible for writeback list handling.
1634	*
1635	* The caller is also responsible for setting the I_SYNC flag beforehand and
1636	* calling inode_sync_complete() to clear it afterwards.
1637	*/
1638	static int
1639	__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1640	{
1641	struct address_space *mapping = inode->i_mapping;
1642	long nr_to_write = wbc->nr_to_write;
1643	unsigned dirty;
1644	int ret;
1645
1646	WARN_ON(!(inode->i_state & I_SYNC));
1647
1648	trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1649
1650	ret = do_writepages(mapping, wbc);
1651
1652	/*
1653	* Make sure to wait on the data before writing out the metadata.
1654	* This is important for filesystems that modify metadata on data
1655	* I/O completion. We don't do it for sync(2) writeback because it has a
1656	* separate, external IO completion path and ->sync_fs for guaranteeing
1657	* inode metadata is written back correctly.
1658	*/
1659	if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1660	int err = filemap_fdatawait(mapping);
1661	if (ret == 0)
1662	ret = err;
1663	}
1664
1665	/*
1666	* If the inode has dirty timestamps and we need to write them, call
1667	* mark_inode_dirty_sync() to notify the filesystem about it and to
1668	* change I_DIRTY_TIME into I_DIRTY_SYNC.
1669	*/
1670	if ((inode->i_state & I_DIRTY_TIME) &&
1671	(wbc->sync_mode == WB_SYNC_ALL ||
1672	time_after(jiffies, inode->dirtied_time_when +
1673	dirtytime_expire_interval * HZ))) {
1674	trace_writeback_lazytime(inode);
1675	mark_inode_dirty_sync(inode);
1676	}
1677
1678	/*
1679	* Get and clear the dirty flags from i_state. This needs to be done
1680	* after calling writepages because some filesystems may redirty the
1681	* inode during writepages due to delalloc. It also needs to be done
1682	* after handling timestamp expiration, as that may dirty the inode too.
1683	*/
1684	spin_lock(lock: &inode->i_lock);
1685	dirty = inode->i_state & I_DIRTY;
1686	inode->i_state &= ~dirty;
1687
1688	/*
1689	* Paired with smp_mb() in __mark_inode_dirty(). This allows
1690	* __mark_inode_dirty() to test i_state without grabbing i_lock -
1691	* either they see the I_DIRTY bits cleared or we see the dirtied
1692	* inode.
1693	*
1694	* I_DIRTY_PAGES is always cleared together above even if @mapping
1695	* still has dirty pages. The flag is reinstated after smp_mb() if
1696	* necessary. This guarantees that either __mark_inode_dirty()
1697	* sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1698	*/
1699	smp_mb();
1700
1701	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1702	inode->i_state |= I_DIRTY_PAGES;
1703	else if (unlikely(inode->i_state & I_PINNING_NETFS_WB)) {
1704	if (!(inode->i_state & I_DIRTY_PAGES)) {
1705	inode->i_state &= ~I_PINNING_NETFS_WB;
1706	wbc->unpinned_netfs_wb = true;
1707	dirty |= I_PINNING_NETFS_WB; /* Cause write_inode */
1708	}
1709	}
1710
1711	spin_unlock(lock: &inode->i_lock);
1712
1713	/* Don't write the inode if only I_DIRTY_PAGES was set */
1714	if (dirty & ~I_DIRTY_PAGES) {
1715	int err = write_inode(inode, wbc);
1716	if (ret == 0)
1717	ret = err;
1718	}
1719	wbc->unpinned_netfs_wb = false;
1720	trace_writeback_single_inode(inode, wbc, nr_to_write);
1721	return ret;
1722	}
1723
1724	/*
1725	* Write out an inode's dirty data and metadata on-demand, i.e. separately from
1726	* the regular batched writeback done by the flusher threads in
1727	* writeback_sb_inodes(). @wbc controls various aspects of the write, such as
1728	* whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
1729	*
1730	* To prevent the inode from going away, either the caller must have a reference
1731	* to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
1732	*/
1733	static int writeback_single_inode(struct inode *inode,
1734	struct writeback_control *wbc)
1735	{
1736	struct bdi_writeback *wb;
1737	int ret = 0;
1738
1739	spin_lock(lock: &inode->i_lock);
1740	if (!atomic_read(v: &inode->i_count))
1741	WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1742	else
1743	WARN_ON(inode->i_state & I_WILL_FREE);
1744
1745	if (inode->i_state & I_SYNC) {
1746	/*
1747	* Writeback is already running on the inode. For WB_SYNC_NONE,
1748	* that's enough and we can just return. For WB_SYNC_ALL, we
1749	* must wait for the existing writeback to complete, then do
1750	* writeback again if there's anything left.
1751	*/
1752	if (wbc->sync_mode != WB_SYNC_ALL)
1753	goto out;
1754	__inode_wait_for_writeback(inode);
1755	}
1756	WARN_ON(inode->i_state & I_SYNC);
1757	/*
1758	* If the inode is already fully clean, then there's nothing to do.
1759	*
1760	* For data-integrity syncs we also need to check whether any pages are
1761	* still under writeback, e.g. due to prior WB_SYNC_NONE writeback. If
1762	* there are any such pages, we'll need to wait for them.
1763	*/
1764	if (!(inode->i_state & I_DIRTY_ALL) &&
1765	(wbc->sync_mode != WB_SYNC_ALL ||
1766	!mapping_tagged(mapping: inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1767	goto out;
1768	inode->i_state |= I_SYNC;
1769	wbc_attach_and_unlock_inode(wbc, inode);
1770
1771	ret = __writeback_single_inode(inode, wbc);
1772
1773	wbc_detach_inode(wbc);
1774
1775	wb = inode_to_wb_and_lock_list(inode);
1776	spin_lock(lock: &inode->i_lock);
1777	/*
1778	* If the inode is freeing, its i_io_list shoudn't be updated
1779	* as it can be finally deleted at this moment.
1780	*/
1781	if (!(inode->i_state & I_FREEING)) {
1782	/*
1783	* If the inode is now fully clean, then it can be safely
1784	* removed from its writeback list (if any). Otherwise the
1785	* flusher threads are responsible for the writeback lists.
1786	*/
1787	if (!(inode->i_state & I_DIRTY_ALL))
1788	inode_cgwb_move_to_attached(inode, wb);
1789	else if (!(inode->i_state & I_SYNC_QUEUED)) {
1790	if ((inode->i_state & I_DIRTY))
1791	redirty_tail_locked(inode, wb);
1792	else if (inode->i_state & I_DIRTY_TIME) {
1793	inode->dirtied_when = jiffies;
1794	inode_io_list_move_locked(inode,
1795	wb,
1796	head: &wb->b_dirty_time);
1797	}
1798	}
1799	}
1800
1801	spin_unlock(lock: &wb->list_lock);
1802	inode_sync_complete(inode);
1803	out:
1804	spin_unlock(lock: &inode->i_lock);
1805	return ret;
1806	}
1807
1808	static long writeback_chunk_size(struct bdi_writeback *wb,
1809	struct wb_writeback_work *work)
1810	{
1811	long pages;
1812
1813	/*
1814	* WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1815	* inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1816	* here avoids calling into writeback_inodes_wb() more than once.
1817	*
1818	* The intended call sequence for WB_SYNC_ALL writeback is:
1819	*
1820	* wb_writeback()
1821	* writeback_sb_inodes() <== called only once
1822	* write_cache_pages() <== called once for each inode
1823	* (quickly) tag currently dirty pages
1824	* (maybe slowly) sync all tagged pages
1825	*/
1826	if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1827	pages = LONG_MAX;
1828	else {
1829	pages = min(wb->avg_write_bandwidth / 2,
1830	global_wb_domain.dirty_limit / DIRTY_SCOPE);
1831	pages = min(pages, work->nr_pages);
1832	pages = round_down(pages + MIN_WRITEBACK_PAGES,
1833	MIN_WRITEBACK_PAGES);
1834	}
1835
1836	return pages;
1837	}
1838
1839	/*
1840	* Write a portion of b_io inodes which belong to @sb.
1841	*
1842	* Return the number of pages and/or inodes written.
1843	*
1844	* NOTE! This is called with wb->list_lock held, and will
1845	* unlock and relock that for each inode it ends up doing
1846	* IO for.
1847	*/
1848	static long writeback_sb_inodes(struct super_block *sb,
1849	struct bdi_writeback *wb,
1850	struct wb_writeback_work *work)
1851	{
1852	struct writeback_control wbc = {
1853	.sync_mode = work->sync_mode,
1854	.tagged_writepages = work->tagged_writepages,
1855	.for_kupdate = work->for_kupdate,
1856	.for_background = work->for_background,
1857	.for_sync = work->for_sync,
1858	.range_cyclic = work->range_cyclic,
1859	.range_start = 0,
1860	.range_end = LLONG_MAX,
1861	};
1862	unsigned long start_time = jiffies;
1863	long write_chunk;
1864	long total_wrote = 0; /* count both pages and inodes */
1865
1866	while (!list_empty(head: &wb->b_io)) {
1867	struct inode *inode = wb_inode(head: wb->b_io.prev);
1868	struct bdi_writeback *tmp_wb;
1869	long wrote;
1870
1871	if (inode->i_sb != sb) {
1872	if (work->sb) {
1873	/*
1874	* We only want to write back data for this
1875	* superblock, move all inodes not belonging
1876	* to it back onto the dirty list.
1877	*/
1878	redirty_tail(inode, wb);
1879	continue;
1880	}
1881
1882	/*
1883	* The inode belongs to a different superblock.
1884	* Bounce back to the caller to unpin this and
1885	* pin the next superblock.
1886	*/
1887	break;
1888	}
1889
1890	/*
1891	* Don't bother with new inodes or inodes being freed, first
1892	* kind does not need periodic writeout yet, and for the latter
1893	* kind writeout is handled by the freer.
1894	*/
1895	spin_lock(lock: &inode->i_lock);
1896	if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1897	redirty_tail_locked(inode, wb);
1898	spin_unlock(lock: &inode->i_lock);
1899	continue;
1900	}
1901	if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1902	/*
1903	* If this inode is locked for writeback and we are not
1904	* doing writeback-for-data-integrity, move it to
1905	* b_more_io so that writeback can proceed with the
1906	* other inodes on s_io.
1907	*
1908	* We'll have another go at writing back this inode
1909	* when we completed a full scan of b_io.
1910	*/
1911	requeue_io(inode, wb);
1912	spin_unlock(lock: &inode->i_lock);
1913	trace_writeback_sb_inodes_requeue(inode);
1914	continue;
1915	}
1916	spin_unlock(lock: &wb->list_lock);
1917
1918	/*
1919	* We already requeued the inode if it had I_SYNC set and we
1920	* are doing WB_SYNC_NONE writeback. So this catches only the
1921	* WB_SYNC_ALL case.
1922	*/
1923	if (inode->i_state & I_SYNC) {
1924	/* Wait for I_SYNC. This function drops i_lock... */
1925	inode_sleep_on_writeback(inode);
1926	/* Inode may be gone, start again */
1927	spin_lock(lock: &wb->list_lock);
1928	continue;
1929	}
1930	inode->i_state |= I_SYNC;
1931	wbc_attach_and_unlock_inode(&wbc, inode);
1932
1933	write_chunk = writeback_chunk_size(wb, work);
1934	wbc.nr_to_write = write_chunk;
1935	wbc.pages_skipped = 0;
1936
1937	/*
1938	* We use I_SYNC to pin the inode in memory. While it is set
1939	* evict_inode() will wait so the inode cannot be freed.
1940	*/
1941	__writeback_single_inode(inode, wbc: &wbc);
1942
1943	wbc_detach_inode(&wbc);
1944	work->nr_pages -= write_chunk - wbc.nr_to_write;
1945	wrote = write_chunk - wbc.nr_to_write - wbc.pages_skipped;
1946	wrote = wrote < 0 ? 0 : wrote;
1947	total_wrote += wrote;
1948
1949	if (need_resched()) {
1950	/*
1951	* We're trying to balance between building up a nice
1952	* long list of IOs to improve our merge rate, and
1953	* getting those IOs out quickly for anyone throttling
1954	* in balance_dirty_pages(). cond_resched() doesn't
1955	* unplug, so get our IOs out the door before we
1956	* give up the CPU.
1957	*/
1958	blk_flush_plug(current->plug, async: false);
1959	cond_resched();
1960	}
1961
1962	/*
1963	* Requeue @inode if still dirty. Be careful as @inode may
1964	* have been switched to another wb in the meantime.
1965	*/
1966	tmp_wb = inode_to_wb_and_lock_list(inode);
1967	spin_lock(lock: &inode->i_lock);
1968	if (!(inode->i_state & I_DIRTY_ALL))
1969	total_wrote++;
1970	requeue_inode(inode, wb: tmp_wb, wbc: &wbc);
1971	inode_sync_complete(inode);
1972	spin_unlock(lock: &inode->i_lock);
1973
1974	if (unlikely(tmp_wb != wb)) {
1975	spin_unlock(lock: &tmp_wb->list_lock);
1976	spin_lock(lock: &wb->list_lock);
1977	}
1978
1979	/*
1980	* bail out to wb_writeback() often enough to check
1981	* background threshold and other termination conditions.
1982	*/
1983	if (total_wrote) {
1984	if (time_is_before_jiffies(start_time + HZ / 10UL))
1985	break;
1986	if (work->nr_pages <= 0)
1987	break;
1988	}
1989	}
1990	return total_wrote;
1991	}
1992
1993	static long __writeback_inodes_wb(struct bdi_writeback *wb,
1994	struct wb_writeback_work *work)
1995	{
1996	unsigned long start_time = jiffies;
1997	long wrote = 0;
1998
1999	while (!list_empty(head: &wb->b_io)) {
2000	struct inode *inode = wb_inode(head: wb->b_io.prev);
2001	struct super_block *sb = inode->i_sb;
2002
2003	if (!super_trylock_shared(sb)) {
2004	/*
2005	* super_trylock_shared() may fail consistently due to
2006	* s_umount being grabbed by someone else. Don't use
2007	* requeue_io() to avoid busy retrying the inode/sb.
2008	*/
2009	redirty_tail(inode, wb);
2010	continue;
2011	}
2012	wrote += writeback_sb_inodes(sb, wb, work);
2013	up_read(sem: &sb->s_umount);
2014
2015	/* refer to the same tests at the end of writeback_sb_inodes */
2016	if (wrote) {
2017	if (time_is_before_jiffies(start_time + HZ / 10UL))
2018	break;
2019	if (work->nr_pages <= 0)
2020	break;
2021	}
2022	}
2023	/* Leave any unwritten inodes on b_io */
2024	return wrote;
2025	}
2026
2027	static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
2028	enum wb_reason reason)
2029	{
2030	struct wb_writeback_work work = {
2031	.nr_pages = nr_pages,
2032	.sync_mode = WB_SYNC_NONE,
2033	.range_cyclic = 1,
2034	.reason = reason,
2035	};
2036	struct blk_plug plug;
2037
2038	blk_start_plug(&plug);
2039	spin_lock(lock: &wb->list_lock);
2040	if (list_empty(head: &wb->b_io))
2041	queue_io(wb, work: &work, dirtied_before: jiffies);
2042	__writeback_inodes_wb(wb, work: &work);
2043	spin_unlock(lock: &wb->list_lock);
2044	blk_finish_plug(&plug);
2045
2046	return nr_pages - work.nr_pages;
2047	}
2048
2049	/*
2050	* Explicit flushing or periodic writeback of "old" data.
2051	*
2052	* Define "old": the first time one of an inode's pages is dirtied, we mark the
2053	* dirtying-time in the inode's address_space. So this periodic writeback code
2054	* just walks the superblock inode list, writing back any inodes which are
2055	* older than a specific point in time.
2056	*
2057	* Try to run once per dirty_writeback_interval. But if a writeback event
2058	* takes longer than a dirty_writeback_interval interval, then leave a
2059	* one-second gap.
2060	*
2061	* dirtied_before takes precedence over nr_to_write. So we'll only write back
2062	* all dirty pages if they are all attached to "old" mappings.
2063	*/
2064	static long wb_writeback(struct bdi_writeback *wb,
2065	struct wb_writeback_work *work)
2066	{
2067	long nr_pages = work->nr_pages;
2068	unsigned long dirtied_before = jiffies;
2069	struct inode *inode;
2070	long progress;
2071	struct blk_plug plug;
2072
2073	blk_start_plug(&plug);
2074	for (;;) {
2075	/*
2076	* Stop writeback when nr_pages has been consumed
2077	*/
2078	if (work->nr_pages <= 0)
2079	break;
2080
2081	/*
2082	* Background writeout and kupdate-style writeback may
2083	* run forever. Stop them if there is other work to do
2084	* so that e.g. sync can proceed. They'll be restarted
2085	* after the other works are all done.
2086	*/
2087	if ((work->for_background || work->for_kupdate) &&
2088	!list_empty(head: &wb->work_list))
2089	break;
2090
2091	/*
2092	* For background writeout, stop when we are below the
2093	* background dirty threshold
2094	*/
2095	if (work->for_background && !wb_over_bg_thresh(wb))
2096	break;
2097
2098
2099	spin_lock(lock: &wb->list_lock);
2100
2101	/*
2102	* Kupdate and background works are special and we want to
2103	* include all inodes that need writing. Livelock avoidance is
2104	* handled by these works yielding to any other work so we are
2105	* safe.
2106	*/
2107	if (work->for_kupdate) {
2108	dirtied_before = jiffies -
2109	msecs_to_jiffies(m: dirty_expire_interval * 10);
2110	} else if (work->for_background)
2111	dirtied_before = jiffies;
2112
2113	trace_writeback_start(wb, work);
2114	if (list_empty(head: &wb->b_io))
2115	queue_io(wb, work, dirtied_before);
2116	if (work->sb)
2117	progress = writeback_sb_inodes(sb: work->sb, wb, work);
2118	else
2119	progress = __writeback_inodes_wb(wb, work);
2120	trace_writeback_written(wb, work);
2121
2122	/*
2123	* Did we write something? Try for more
2124	*
2125	* Dirty inodes are moved to b_io for writeback in batches.
2126	* The completion of the current batch does not necessarily
2127	* mean the overall work is done. So we keep looping as long
2128	* as made some progress on cleaning pages or inodes.
2129	*/
2130	if (progress) {
2131	spin_unlock(lock: &wb->list_lock);
2132	continue;
2133	}
2134
2135	/*
2136	* No more inodes for IO, bail
2137	*/
2138	if (list_empty(head: &wb->b_more_io)) {
2139	spin_unlock(lock: &wb->list_lock);
2140	break;
2141	}
2142
2143	/*
2144	* Nothing written. Wait for some inode to
2145	* become available for writeback. Otherwise
2146	* we'll just busyloop.
2147	*/
2148	trace_writeback_wait(wb, work);
2149	inode = wb_inode(head: wb->b_more_io.prev);
2150	spin_lock(lock: &inode->i_lock);
2151	spin_unlock(lock: &wb->list_lock);
2152	/* This function drops i_lock... */
2153	inode_sleep_on_writeback(inode);
2154	}
2155	blk_finish_plug(&plug);
2156
2157	return nr_pages - work->nr_pages;
2158	}
2159
2160	/*
2161	* Return the next wb_writeback_work struct that hasn't been processed yet.
2162	*/
2163	static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
2164	{
2165	struct wb_writeback_work *work = NULL;
2166
2167	spin_lock_irq(lock: &wb->work_lock);
2168	if (!list_empty(head: &wb->work_list)) {
2169	work = list_entry(wb->work_list.next,
2170	struct wb_writeback_work, list);
2171	list_del_init(entry: &work->list);
2172	}
2173	spin_unlock_irq(lock: &wb->work_lock);
2174	return work;
2175	}
2176
2177	static long wb_check_background_flush(struct bdi_writeback *wb)
2178	{
2179	if (wb_over_bg_thresh(wb)) {
2180
2181	struct wb_writeback_work work = {
2182	.nr_pages = LONG_MAX,
2183	.sync_mode = WB_SYNC_NONE,
2184	.for_background = 1,
2185	.range_cyclic = 1,
2186	.reason = WB_REASON_BACKGROUND,
2187	};
2188
2189	return wb_writeback(wb, work: &work);
2190	}
2191
2192	return 0;
2193	}
2194
2195	static long wb_check_old_data_flush(struct bdi_writeback *wb)
2196	{
2197	unsigned long expired;
2198	long nr_pages;
2199
2200	/*
2201	* When set to zero, disable periodic writeback
2202	*/
2203	if (!dirty_writeback_interval)
2204	return 0;
2205
2206	expired = wb->last_old_flush +
2207	msecs_to_jiffies(m: dirty_writeback_interval * 10);
2208	if (time_before(jiffies, expired))
2209	return 0;
2210
2211	wb->last_old_flush = jiffies;
2212	nr_pages = get_nr_dirty_pages();
2213
2214	if (nr_pages) {
2215	struct wb_writeback_work work = {
2216	.nr_pages = nr_pages,
2217	.sync_mode = WB_SYNC_NONE,
2218	.for_kupdate = 1,
2219	.range_cyclic = 1,
2220	.reason = WB_REASON_PERIODIC,
2221	};
2222
2223	return wb_writeback(wb, work: &work);
2224	}
2225
2226	return 0;
2227	}
2228
2229	static long wb_check_start_all(struct bdi_writeback *wb)
2230	{
2231	long nr_pages;
2232
2233	if (!test_bit(WB_start_all, &wb->state))
2234	return 0;
2235
2236	nr_pages = get_nr_dirty_pages();
2237	if (nr_pages) {
2238	struct wb_writeback_work work = {
2239	.nr_pages = wb_split_bdi_pages(wb, nr_pages),
2240	.sync_mode = WB_SYNC_NONE,
2241	.range_cyclic = 1,
2242	.reason = wb->start_all_reason,
2243	};
2244
2245	nr_pages = wb_writeback(wb, work: &work);
2246	}
2247
2248	clear_bit(nr: WB_start_all, addr: &wb->state);
2249	return nr_pages;
2250	}
2251
2252
2253	/*
2254	* Retrieve work items and do the writeback they describe
2255	*/
2256	static long wb_do_writeback(struct bdi_writeback *wb)
2257	{
2258	struct wb_writeback_work *work;
2259	long wrote = 0;
2260
2261	set_bit(nr: WB_writeback_running, addr: &wb->state);
2262	while ((work = get_next_work_item(wb)) != NULL) {
2263	trace_writeback_exec(wb, work);
2264	wrote += wb_writeback(wb, work);
2265	finish_writeback_work(wb, work);
2266	}
2267
2268	/*
2269	* Check for a flush-everything request
2270	*/
2271	wrote += wb_check_start_all(wb);
2272
2273	/*
2274	* Check for periodic writeback, kupdated() style
2275	*/
2276	wrote += wb_check_old_data_flush(wb);
2277	wrote += wb_check_background_flush(wb);
2278	clear_bit(nr: WB_writeback_running, addr: &wb->state);
2279
2280	return wrote;
2281	}
2282
2283	/*
2284	* Handle writeback of dirty data for the device backed by this bdi. Also
2285	* reschedules periodically and does kupdated style flushing.
2286	*/
2287	void wb_workfn(struct work_struct *work)
2288	{
2289	struct bdi_writeback *wb = container_of(to_delayed_work(work),
2290	struct bdi_writeback, dwork);
2291	long pages_written;
2292
2293	set_worker_desc("flush-%s", bdi_dev_name(bdi: wb->bdi));
2294
2295	if (likely(!current_is_workqueue_rescuer() ||
2296	!test_bit(WB_registered, &wb->state))) {
2297	/*
2298	* The normal path. Keep writing back @wb until its
2299	* work_list is empty. Note that this path is also taken
2300	* if @wb is shutting down even when we're running off the
2301	* rescuer as work_list needs to be drained.
2302	*/
2303	do {
2304	pages_written = wb_do_writeback(wb);
2305	trace_writeback_pages_written(pages_written);
2306	} while (!list_empty(head: &wb->work_list));
2307	} else {
2308	/*
2309	* bdi_wq can't get enough workers and we're running off
2310	* the emergency worker. Don't hog it. Hopefully, 1024 is
2311	* enough for efficient IO.
2312	*/
2313	pages_written = writeback_inodes_wb(wb, nr_pages: 1024,
2314	reason: WB_REASON_FORKER_THREAD);
2315	trace_writeback_pages_written(pages_written);
2316	}
2317
2318	if (!list_empty(head: &wb->work_list))
2319	wb_wakeup(wb);
2320	else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
2321	wb_wakeup_delayed(wb);
2322	}
2323
2324	/*
2325	* Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
2326	* write back the whole world.
2327	*/
2328	static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2329	enum wb_reason reason)
2330	{
2331	struct bdi_writeback *wb;
2332
2333	if (!bdi_has_dirty_io(bdi))
2334	return;
2335
2336	list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2337	wb_start_writeback(wb, reason);
2338	}
2339
2340	void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2341	enum wb_reason reason)
2342	{
2343	rcu_read_lock();
2344	__wakeup_flusher_threads_bdi(bdi, reason);
2345	rcu_read_unlock();
2346	}
2347
2348	/*
2349	* Wakeup the flusher threads to start writeback of all currently dirty pages
2350	*/
2351	void wakeup_flusher_threads(enum wb_reason reason)
2352	{
2353	struct backing_dev_info *bdi;
2354
2355	/*
2356	* If we are expecting writeback progress we must submit plugged IO.
2357	*/
2358	blk_flush_plug(current->plug, async: true);
2359
2360	rcu_read_lock();
2361	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2362	__wakeup_flusher_threads_bdi(bdi, reason);
2363	rcu_read_unlock();
2364	}
2365
2366	/*
2367	* Wake up bdi's periodically to make sure dirtytime inodes gets
2368	* written back periodically. We deliberately do *not* check the
2369	* b_dirtytime list in wb_has_dirty_io(), since this would cause the
2370	* kernel to be constantly waking up once there are any dirtytime
2371	* inodes on the system. So instead we define a separate delayed work
2372	* function which gets called much more rarely. (By default, only
2373	* once every 12 hours.)
2374	*
2375	* If there is any other write activity going on in the file system,
2376	* this function won't be necessary. But if the only thing that has
2377	* happened on the file system is a dirtytime inode caused by an atime
2378	* update, we need this infrastructure below to make sure that inode
2379	* eventually gets pushed out to disk.
2380	*/
2381	static void wakeup_dirtytime_writeback(struct work_struct *w);
2382	static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2383
2384	static void wakeup_dirtytime_writeback(struct work_struct *w)
2385	{
2386	struct backing_dev_info *bdi;
2387
2388	rcu_read_lock();
2389	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
2390	struct bdi_writeback *wb;
2391
2392	list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2393	if (!list_empty(head: &wb->b_dirty_time))
2394	wb_wakeup(wb);
2395	}
2396	rcu_read_unlock();
2397	schedule_delayed_work(dwork: &dirtytime_work, delay: dirtytime_expire_interval * HZ);
2398	}
2399
2400	static int __init start_dirtytime_writeback(void)
2401	{
2402	schedule_delayed_work(dwork: &dirtytime_work, delay: dirtytime_expire_interval * HZ);
2403	return 0;
2404	}
2405	__initcall(start_dirtytime_writeback);
2406
2407	int dirtytime_interval_handler(struct ctl_table *table, int write,
2408	void *buffer, size_t *lenp, loff_t *ppos)
2409	{
2410	int ret;
2411
2412	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2413	if (ret == 0 && write)
2414	mod_delayed_work(wq: system_wq, dwork: &dirtytime_work, delay: 0);
2415	return ret;
2416	}
2417
2418	/**
2419	* __mark_inode_dirty - internal function to mark an inode dirty
2420	*
2421	* @inode: inode to mark
2422	* @flags: what kind of dirty, e.g. I_DIRTY_SYNC. This can be a combination of
2423	* multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
2424	* with I_DIRTY_PAGES.
2425	*
2426	* Mark an inode as dirty. We notify the filesystem, then update the inode's
2427	* dirty flags. Then, if needed we add the inode to the appropriate dirty list.
2428	*
2429	* Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
2430	* instead of calling this directly.
2431	*
2432	* CAREFUL! We only add the inode to the dirty list if it is hashed or if it
2433	* refers to a blockdev. Unhashed inodes will never be added to the dirty list
2434	* even if they are later hashed, as they will have been marked dirty already.
2435	*
2436	* In short, ensure you hash any inodes _before_ you start marking them dirty.
2437	*
2438	* Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2439	* the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
2440	* the kernel-internal blockdev inode represents the dirtying time of the
2441	* blockdev's pages. This is why for I_DIRTY_PAGES we always use
2442	* page->mapping->host, so the page-dirtying time is recorded in the internal
2443	* blockdev inode.
2444	*/
2445	void __mark_inode_dirty(struct inode *inode, int flags)
2446	{
2447	struct super_block *sb = inode->i_sb;
2448	int dirtytime = 0;
2449	struct bdi_writeback *wb = NULL;
2450
2451	trace_writeback_mark_inode_dirty(inode, flags);
2452
2453	if (flags & I_DIRTY_INODE) {
2454	/*
2455	* Inode timestamp update will piggback on this dirtying.
2456	* We tell ->dirty_inode callback that timestamps need to
2457	* be updated by setting I_DIRTY_TIME in flags.
2458	*/
2459	if (inode->i_state & I_DIRTY_TIME) {
2460	spin_lock(lock: &inode->i_lock);
2461	if (inode->i_state & I_DIRTY_TIME) {
2462	inode->i_state &= ~I_DIRTY_TIME;
2463	flags |= I_DIRTY_TIME;
2464	}
2465	spin_unlock(lock: &inode->i_lock);
2466	}
2467
2468	/*
2469	* Notify the filesystem about the inode being dirtied, so that
2470	* (if needed) it can update on-disk fields and journal the
2471	* inode. This is only needed when the inode itself is being
2472	* dirtied now. I.e. it's only needed for I_DIRTY_INODE, not
2473	* for just I_DIRTY_PAGES or I_DIRTY_TIME.
2474	*/
2475	trace_writeback_dirty_inode_start(inode, flags);
2476	if (sb->s_op->dirty_inode)
2477	sb->s_op->dirty_inode(inode,
2478	flags & (I_DIRTY_INODE | I_DIRTY_TIME));
2479	trace_writeback_dirty_inode(inode, flags);
2480
2481	/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
2482	flags &= ~I_DIRTY_TIME;
2483	} else {
2484	/*
2485	* Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
2486	* (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
2487	* in one call to __mark_inode_dirty().)
2488	*/
2489	dirtytime = flags & I_DIRTY_TIME;
2490	WARN_ON_ONCE(dirtytime && flags != I_DIRTY_TIME);
2491	}
2492
2493	/*
2494	* Paired with smp_mb() in __writeback_single_inode() for the
2495	* following lockless i_state test. See there for details.
2496	*/
2497	smp_mb();
2498
2499	if ((inode->i_state & flags) == flags)
2500	return;
2501
2502	spin_lock(lock: &inode->i_lock);
2503	if ((inode->i_state & flags) != flags) {
2504	const int was_dirty = inode->i_state & I_DIRTY;
2505
2506	inode_attach_wb(inode, NULL);
2507
2508	inode->i_state |= flags;
2509
2510	/*
2511	* Grab inode's wb early because it requires dropping i_lock and we
2512	* need to make sure following checks happen atomically with dirty
2513	* list handling so that we don't move inodes under flush worker's
2514	* hands.
2515	*/
2516	if (!was_dirty) {
2517	wb = locked_inode_to_wb_and_lock_list(inode);
2518	spin_lock(lock: &inode->i_lock);
2519	}
2520
2521	/*
2522	* If the inode is queued for writeback by flush worker, just
2523	* update its dirty state. Once the flush worker is done with
2524	* the inode it will place it on the appropriate superblock
2525	* list, based upon its state.
2526	*/
2527	if (inode->i_state & I_SYNC_QUEUED)
2528	goto out_unlock;
2529
2530	/*
2531	* Only add valid (hashed) inodes to the superblock's
2532	* dirty list. Add blockdev inodes as well.
2533	*/
2534	if (!S_ISBLK(inode->i_mode)) {
2535	if (inode_unhashed(inode))
2536	goto out_unlock;
2537	}
2538	if (inode->i_state & I_FREEING)
2539	goto out_unlock;
2540
2541	/*
2542	* If the inode was already on b_dirty/b_io/b_more_io, don't
2543	* reposition it (that would break b_dirty time-ordering).
2544	*/
2545	if (!was_dirty) {
2546	struct list_head *dirty_list;
2547	bool wakeup_bdi = false;
2548
2549	inode->dirtied_when = jiffies;
2550	if (dirtytime)
2551	inode->dirtied_time_when = jiffies;
2552
2553	if (inode->i_state & I_DIRTY)
2554	dirty_list = &wb->b_dirty;
2555	else
2556	dirty_list = &wb->b_dirty_time;
2557
2558	wakeup_bdi = inode_io_list_move_locked(inode, wb,
2559	head: dirty_list);
2560
2561	spin_unlock(lock: &wb->list_lock);
2562	spin_unlock(lock: &inode->i_lock);
2563	trace_writeback_dirty_inode_enqueue(inode);
2564
2565	/*
2566	* If this is the first dirty inode for this bdi,
2567	* we have to wake-up the corresponding bdi thread
2568	* to make sure background write-back happens
2569	* later.
2570	*/
2571	if (wakeup_bdi &&
2572	(wb->bdi->capabilities & BDI_CAP_WRITEBACK))
2573	wb_wakeup_delayed(wb);
2574	return;
2575	}
2576	}
2577	out_unlock:
2578	if (wb)
2579	spin_unlock(lock: &wb->list_lock);
2580	spin_unlock(lock: &inode->i_lock);
2581	}
2582	EXPORT_SYMBOL(__mark_inode_dirty);
2583
2584	/*
2585	* The @s_sync_lock is used to serialise concurrent sync operations
2586	* to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2587	* Concurrent callers will block on the s_sync_lock rather than doing contending
2588	* walks. The queueing maintains sync(2) required behaviour as all the IO that
2589	* has been issued up to the time this function is enter is guaranteed to be
2590	* completed by the time we have gained the lock and waited for all IO that is
2591	* in progress regardless of the order callers are granted the lock.
2592	*/
2593	static void wait_sb_inodes(struct super_block *sb)
2594	{
2595	LIST_HEAD(sync_list);
2596
2597	/*
2598	* We need to be protected against the filesystem going from
2599	* r/o to r/w or vice versa.
2600	*/
2601	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2602
2603	mutex_lock(&sb->s_sync_lock);
2604
2605	/*
2606	* Splice the writeback list onto a temporary list to avoid waiting on
2607	* inodes that have started writeback after this point.
2608	*
2609	* Use rcu_read_lock() to keep the inodes around until we have a
2610	* reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2611	* the local list because inodes can be dropped from either by writeback
2612	* completion.
2613	*/
2614	rcu_read_lock();
2615	spin_lock_irq(lock: &sb->s_inode_wblist_lock);
2616	list_splice_init(list: &sb->s_inodes_wb, head: &sync_list);
2617
2618	/*
2619	* Data integrity sync. Must wait for all pages under writeback, because
2620	* there may have been pages dirtied before our sync call, but which had
2621	* writeout started before we write it out. In which case, the inode
2622	* may not be on the dirty list, but we still have to wait for that
2623	* writeout.
2624	*/
2625	while (!list_empty(head: &sync_list)) {
2626	struct inode *inode = list_first_entry(&sync_list, struct inode,
2627	i_wb_list);
2628	struct address_space *mapping = inode->i_mapping;
2629
2630	/*
2631	* Move each inode back to the wb list before we drop the lock
2632	* to preserve consistency between i_wb_list and the mapping
2633	* writeback tag. Writeback completion is responsible to remove
2634	* the inode from either list once the writeback tag is cleared.
2635	*/
2636	list_move_tail(list: &inode->i_wb_list, head: &sb->s_inodes_wb);
2637
2638	/*
2639	* The mapping can appear untagged while still on-list since we
2640	* do not have the mapping lock. Skip it here, wb completion
2641	* will remove it.
2642	*/
2643	if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2644	continue;
2645
2646	spin_unlock_irq(lock: &sb->s_inode_wblist_lock);
2647
2648	spin_lock(lock: &inode->i_lock);
2649	if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
2650	spin_unlock(lock: &inode->i_lock);
2651
2652	spin_lock_irq(lock: &sb->s_inode_wblist_lock);
2653	continue;
2654	}
2655	__iget(inode);
2656	spin_unlock(lock: &inode->i_lock);
2657	rcu_read_unlock();
2658
2659	/*
2660	* We keep the error status of individual mapping so that
2661	* applications can catch the writeback error using fsync(2).
2662	* See filemap_fdatawait_keep_errors() for details.
2663	*/
2664	filemap_fdatawait_keep_errors(mapping);
2665
2666	cond_resched();
2667
2668	iput(inode);
2669
2670	rcu_read_lock();
2671	spin_lock_irq(lock: &sb->s_inode_wblist_lock);
2672	}
2673	spin_unlock_irq(lock: &sb->s_inode_wblist_lock);
2674	rcu_read_unlock();
2675	mutex_unlock(lock: &sb->s_sync_lock);
2676	}
2677
2678	static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2679	enum wb_reason reason, bool skip_if_busy)
2680	{
2681	struct backing_dev_info *bdi = sb->s_bdi;
2682	DEFINE_WB_COMPLETION(done, bdi);
2683	struct wb_writeback_work work = {
2684	.sb = sb,
2685	.sync_mode = WB_SYNC_NONE,
2686	.tagged_writepages = 1,
2687	.done = &done,
2688	.nr_pages = nr,
2689	.reason = reason,
2690	};
2691
2692	if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2693	return;
2694	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2695
2696	bdi_split_work_to_wbs(bdi: sb->s_bdi, base_work: &work, skip_if_busy);
2697	wb_wait_for_completion(done: &done);
2698	}
2699
2700	/**
2701	* writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2702	* @sb: the superblock
2703	* @nr: the number of pages to write
2704	* @reason: reason why some writeback work initiated
2705	*
2706	* Start writeback on some inodes on this super_block. No guarantees are made
2707	* on how many (if any) will be written, and this function does not wait
2708	* for IO completion of submitted IO.
2709	*/
2710	void writeback_inodes_sb_nr(struct super_block *sb,
2711	unsigned long nr,
2712	enum wb_reason reason)
2713	{
2714	__writeback_inodes_sb_nr(sb, nr, reason, skip_if_busy: false);
2715	}
2716	EXPORT_SYMBOL(writeback_inodes_sb_nr);
2717
2718	/**
2719	* writeback_inodes_sb - writeback dirty inodes from given super_block
2720	* @sb: the superblock
2721	* @reason: reason why some writeback work was initiated
2722	*
2723	* Start writeback on some inodes on this super_block. No guarantees are made
2724	* on how many (if any) will be written, and this function does not wait
2725	* for IO completion of submitted IO.
2726	*/
2727	void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2728	{
2729	return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2730	}
2731	EXPORT_SYMBOL(writeback_inodes_sb);
2732
2733	/**
2734	* try_to_writeback_inodes_sb - try to start writeback if none underway
2735	* @sb: the superblock
2736	* @reason: reason why some writeback work was initiated
2737	*
2738	* Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2739	*/
2740	void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2741	{
2742	if (!down_read_trylock(sem: &sb->s_umount))
2743	return;
2744
2745	__writeback_inodes_sb_nr(sb, nr: get_nr_dirty_pages(), reason, skip_if_busy: true);
2746	up_read(sem: &sb->s_umount);
2747	}
2748	EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2749
2750	/**
2751	* sync_inodes_sb - sync sb inode pages
2752	* @sb: the superblock
2753	*
2754	* This function writes and waits on any dirty inode belonging to this
2755	* super_block.
2756	*/
2757	void sync_inodes_sb(struct super_block *sb)
2758	{
2759	struct backing_dev_info *bdi = sb->s_bdi;
2760	DEFINE_WB_COMPLETION(done, bdi);
2761	struct wb_writeback_work work = {
2762	.sb = sb,
2763	.sync_mode = WB_SYNC_ALL,
2764	.nr_pages = LONG_MAX,
2765	.range_cyclic = 0,
2766	.done = &done,
2767	.reason = WB_REASON_SYNC,
2768	.for_sync = 1,
2769	};
2770
2771	/*
2772	* Can't skip on !bdi_has_dirty() because we should wait for !dirty
2773	* inodes under writeback and I_DIRTY_TIME inodes ignored by
2774	* bdi_has_dirty() need to be written out too.
2775	*/
2776	if (bdi == &noop_backing_dev_info)
2777	return;
2778	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2779
2780	/* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2781	bdi_down_write_wb_switch_rwsem(bdi);
2782	bdi_split_work_to_wbs(bdi, base_work: &work, skip_if_busy: false);
2783	wb_wait_for_completion(done: &done);
2784	bdi_up_write_wb_switch_rwsem(bdi);
2785
2786	wait_sb_inodes(sb);
2787	}
2788	EXPORT_SYMBOL(sync_inodes_sb);
2789
2790	/**
2791	* write_inode_now - write an inode to disk
2792	* @inode: inode to write to disk
2793	* @sync: whether the write should be synchronous or not
2794	*
2795	* This function commits an inode to disk immediately if it is dirty. This is
2796	* primarily needed by knfsd.
2797	*
2798	* The caller must either have a ref on the inode or must have set I_WILL_FREE.
2799	*/
2800	int write_inode_now(struct inode *inode, int sync)
2801	{
2802	struct writeback_control wbc = {
2803	.nr_to_write = LONG_MAX,
2804	.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2805	.range_start = 0,
2806	.range_end = LLONG_MAX,
2807	};
2808
2809	if (!mapping_can_writeback(mapping: inode->i_mapping))
2810	wbc.nr_to_write = 0;
2811
2812	might_sleep();
2813	return writeback_single_inode(inode, wbc: &wbc);
2814	}
2815	EXPORT_SYMBOL(write_inode_now);
2816
2817	/**
2818	* sync_inode_metadata - write an inode to disk
2819	* @inode: the inode to sync
2820	* @wait: wait for I/O to complete.
2821	*
2822	* Write an inode to disk and adjust its dirty state after completion.
2823	*
2824	* Note: only writes the actual inode, no associated data or other metadata.
2825	*/
2826	int sync_inode_metadata(struct inode *inode, int wait)
2827	{
2828	struct writeback_control wbc = {
2829	.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2830	.nr_to_write = 0, /* metadata-only */
2831	};
2832
2833	return writeback_single_inode(inode, wbc: &wbc);
2834	}
2835	EXPORT_SYMBOL(sync_inode_metadata);
2836