1 | /* SPDX-License-Identifier: GPL-2.0+ */ |
2 | /* |
3 | * Read-Copy Update mechanism for mutual exclusion (tree-based version) |
4 | * Internal non-public definitions that provide either classic |
5 | * or preemptible semantics. |
6 | * |
7 | * Copyright Red Hat, 2009 |
8 | * Copyright IBM Corporation, 2009 |
9 | * |
10 | * Author: Ingo Molnar <mingo@elte.hu> |
11 | * Paul E. McKenney <paulmck@linux.ibm.com> |
12 | */ |
13 | |
14 | #include "../locking/rtmutex_common.h" |
15 | |
16 | static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) |
17 | { |
18 | /* |
19 | * In order to read the offloaded state of an rdp in a safe |
20 | * and stable way and prevent from its value to be changed |
21 | * under us, we must either hold the barrier mutex, the cpu |
22 | * hotplug lock (read or write) or the nocb lock. Local |
23 | * non-preemptible reads are also safe. NOCB kthreads and |
24 | * timers have their own means of synchronization against the |
25 | * offloaded state updaters. |
26 | */ |
27 | RCU_LOCKDEP_WARN( |
28 | !(lockdep_is_held(&rcu_state.barrier_mutex) || |
29 | (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) || |
30 | rcu_lockdep_is_held_nocb(rdp) || |
31 | (rdp == this_cpu_ptr(&rcu_data) && |
32 | !(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) || |
33 | rcu_current_is_nocb_kthread(rdp)), |
34 | "Unsafe read of RCU_NOCB offloaded state" |
35 | ); |
36 | |
37 | return rcu_segcblist_is_offloaded(rsclp: &rdp->cblist); |
38 | } |
39 | |
40 | /* |
41 | * Check the RCU kernel configuration parameters and print informative |
42 | * messages about anything out of the ordinary. |
43 | */ |
44 | static void __init rcu_bootup_announce_oddness(void) |
45 | { |
46 | if (IS_ENABLED(CONFIG_RCU_TRACE)) |
47 | pr_info("\tRCU event tracing is enabled.\n" ); |
48 | if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) || |
49 | (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32)) |
50 | pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n" , |
51 | RCU_FANOUT); |
52 | if (rcu_fanout_exact) |
53 | pr_info("\tHierarchical RCU autobalancing is disabled.\n" ); |
54 | if (IS_ENABLED(CONFIG_PROVE_RCU)) |
55 | pr_info("\tRCU lockdep checking is enabled.\n" ); |
56 | if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) |
57 | pr_info("\tRCU strict (and thus non-scalable) grace periods are enabled.\n" ); |
58 | if (RCU_NUM_LVLS >= 4) |
59 | pr_info("\tFour(or more)-level hierarchy is enabled.\n" ); |
60 | if (RCU_FANOUT_LEAF != 16) |
61 | pr_info("\tBuild-time adjustment of leaf fanout to %d.\n" , |
62 | RCU_FANOUT_LEAF); |
63 | if (rcu_fanout_leaf != RCU_FANOUT_LEAF) |
64 | pr_info("\tBoot-time adjustment of leaf fanout to %d.\n" , |
65 | rcu_fanout_leaf); |
66 | if (nr_cpu_ids != NR_CPUS) |
67 | pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n" , NR_CPUS, nr_cpu_ids); |
68 | #ifdef CONFIG_RCU_BOOST |
69 | pr_info("\tRCU priority boosting: priority %d delay %d ms.\n" , |
70 | kthread_prio, CONFIG_RCU_BOOST_DELAY); |
71 | #endif |
72 | if (blimit != DEFAULT_RCU_BLIMIT) |
73 | pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n" , blimit); |
74 | if (qhimark != DEFAULT_RCU_QHIMARK) |
75 | pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n" , qhimark); |
76 | if (qlowmark != DEFAULT_RCU_QLOMARK) |
77 | pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n" , qlowmark); |
78 | if (qovld != DEFAULT_RCU_QOVLD) |
79 | pr_info("\tBoot-time adjustment of callback overload level to %ld.\n" , qovld); |
80 | if (jiffies_till_first_fqs != ULONG_MAX) |
81 | pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n" , jiffies_till_first_fqs); |
82 | if (jiffies_till_next_fqs != ULONG_MAX) |
83 | pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n" , jiffies_till_next_fqs); |
84 | if (jiffies_till_sched_qs != ULONG_MAX) |
85 | pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n" , jiffies_till_sched_qs); |
86 | if (rcu_kick_kthreads) |
87 | pr_info("\tKick kthreads if too-long grace period.\n" ); |
88 | if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD)) |
89 | pr_info("\tRCU callback double-/use-after-free debug is enabled.\n" ); |
90 | if (gp_preinit_delay) |
91 | pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n" , gp_preinit_delay); |
92 | if (gp_init_delay) |
93 | pr_info("\tRCU debug GP init slowdown %d jiffies.\n" , gp_init_delay); |
94 | if (gp_cleanup_delay) |
95 | pr_info("\tRCU debug GP cleanup slowdown %d jiffies.\n" , gp_cleanup_delay); |
96 | if (!use_softirq) |
97 | pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n" ); |
98 | if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG)) |
99 | pr_info("\tRCU debug extended QS entry/exit.\n" ); |
100 | rcupdate_announce_bootup_oddness(); |
101 | } |
102 | |
103 | #ifdef CONFIG_PREEMPT_RCU |
104 | |
105 | static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake); |
106 | static void rcu_read_unlock_special(struct task_struct *t); |
107 | |
108 | /* |
109 | * Tell them what RCU they are running. |
110 | */ |
111 | static void __init rcu_bootup_announce(void) |
112 | { |
113 | pr_info("Preemptible hierarchical RCU implementation.\n" ); |
114 | rcu_bootup_announce_oddness(); |
115 | } |
116 | |
117 | /* Flags for rcu_preempt_ctxt_queue() decision table. */ |
118 | #define RCU_GP_TASKS 0x8 |
119 | #define RCU_EXP_TASKS 0x4 |
120 | #define RCU_GP_BLKD 0x2 |
121 | #define RCU_EXP_BLKD 0x1 |
122 | |
123 | /* |
124 | * Queues a task preempted within an RCU-preempt read-side critical |
125 | * section into the appropriate location within the ->blkd_tasks list, |
126 | * depending on the states of any ongoing normal and expedited grace |
127 | * periods. The ->gp_tasks pointer indicates which element the normal |
128 | * grace period is waiting on (NULL if none), and the ->exp_tasks pointer |
129 | * indicates which element the expedited grace period is waiting on (again, |
130 | * NULL if none). If a grace period is waiting on a given element in the |
131 | * ->blkd_tasks list, it also waits on all subsequent elements. Thus, |
132 | * adding a task to the tail of the list blocks any grace period that is |
133 | * already waiting on one of the elements. In contrast, adding a task |
134 | * to the head of the list won't block any grace period that is already |
135 | * waiting on one of the elements. |
136 | * |
137 | * This queuing is imprecise, and can sometimes make an ongoing grace |
138 | * period wait for a task that is not strictly speaking blocking it. |
139 | * Given the choice, we needlessly block a normal grace period rather than |
140 | * blocking an expedited grace period. |
141 | * |
142 | * Note that an endless sequence of expedited grace periods still cannot |
143 | * indefinitely postpone a normal grace period. Eventually, all of the |
144 | * fixed number of preempted tasks blocking the normal grace period that are |
145 | * not also blocking the expedited grace period will resume and complete |
146 | * their RCU read-side critical sections. At that point, the ->gp_tasks |
147 | * pointer will equal the ->exp_tasks pointer, at which point the end of |
148 | * the corresponding expedited grace period will also be the end of the |
149 | * normal grace period. |
150 | */ |
151 | static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) |
152 | __releases(rnp->lock) /* But leaves rrupts disabled. */ |
153 | { |
154 | int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) + |
155 | (rnp->exp_tasks ? RCU_EXP_TASKS : 0) + |
156 | (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) + |
157 | (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0); |
158 | struct task_struct *t = current; |
159 | |
160 | raw_lockdep_assert_held_rcu_node(rnp); |
161 | WARN_ON_ONCE(rdp->mynode != rnp); |
162 | WARN_ON_ONCE(!rcu_is_leaf_node(rnp)); |
163 | /* RCU better not be waiting on newly onlined CPUs! */ |
164 | WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask & |
165 | rdp->grpmask); |
166 | |
167 | /* |
168 | * Decide where to queue the newly blocked task. In theory, |
169 | * this could be an if-statement. In practice, when I tried |
170 | * that, it was quite messy. |
171 | */ |
172 | switch (blkd_state) { |
173 | case 0: |
174 | case RCU_EXP_TASKS: |
175 | case RCU_EXP_TASKS + RCU_GP_BLKD: |
176 | case RCU_GP_TASKS: |
177 | case RCU_GP_TASKS + RCU_EXP_TASKS: |
178 | |
179 | /* |
180 | * Blocking neither GP, or first task blocking the normal |
181 | * GP but not blocking the already-waiting expedited GP. |
182 | * Queue at the head of the list to avoid unnecessarily |
183 | * blocking the already-waiting GPs. |
184 | */ |
185 | list_add(new: &t->rcu_node_entry, head: &rnp->blkd_tasks); |
186 | break; |
187 | |
188 | case RCU_EXP_BLKD: |
189 | case RCU_GP_BLKD: |
190 | case RCU_GP_BLKD + RCU_EXP_BLKD: |
191 | case RCU_GP_TASKS + RCU_EXP_BLKD: |
192 | case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: |
193 | case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: |
194 | |
195 | /* |
196 | * First task arriving that blocks either GP, or first task |
197 | * arriving that blocks the expedited GP (with the normal |
198 | * GP already waiting), or a task arriving that blocks |
199 | * both GPs with both GPs already waiting. Queue at the |
200 | * tail of the list to avoid any GP waiting on any of the |
201 | * already queued tasks that are not blocking it. |
202 | */ |
203 | list_add_tail(new: &t->rcu_node_entry, head: &rnp->blkd_tasks); |
204 | break; |
205 | |
206 | case RCU_EXP_TASKS + RCU_EXP_BLKD: |
207 | case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: |
208 | case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD: |
209 | |
210 | /* |
211 | * Second or subsequent task blocking the expedited GP. |
212 | * The task either does not block the normal GP, or is the |
213 | * first task blocking the normal GP. Queue just after |
214 | * the first task blocking the expedited GP. |
215 | */ |
216 | list_add(new: &t->rcu_node_entry, head: rnp->exp_tasks); |
217 | break; |
218 | |
219 | case RCU_GP_TASKS + RCU_GP_BLKD: |
220 | case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD: |
221 | |
222 | /* |
223 | * Second or subsequent task blocking the normal GP. |
224 | * The task does not block the expedited GP. Queue just |
225 | * after the first task blocking the normal GP. |
226 | */ |
227 | list_add(new: &t->rcu_node_entry, head: rnp->gp_tasks); |
228 | break; |
229 | |
230 | default: |
231 | |
232 | /* Yet another exercise in excessive paranoia. */ |
233 | WARN_ON_ONCE(1); |
234 | break; |
235 | } |
236 | |
237 | /* |
238 | * We have now queued the task. If it was the first one to |
239 | * block either grace period, update the ->gp_tasks and/or |
240 | * ->exp_tasks pointers, respectively, to reference the newly |
241 | * blocked tasks. |
242 | */ |
243 | if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) { |
244 | WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry); |
245 | WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq); |
246 | } |
247 | if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD)) |
248 | WRITE_ONCE(rnp->exp_tasks, &t->rcu_node_entry); |
249 | WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) != |
250 | !(rnp->qsmask & rdp->grpmask)); |
251 | WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) != |
252 | !(rnp->expmask & rdp->grpmask)); |
253 | raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */ |
254 | |
255 | /* |
256 | * Report the quiescent state for the expedited GP. This expedited |
257 | * GP should not be able to end until we report, so there should be |
258 | * no need to check for a subsequent expedited GP. (Though we are |
259 | * still in a quiescent state in any case.) |
260 | * |
261 | * Interrupts are disabled, so ->cpu_no_qs.b.exp cannot change. |
262 | */ |
263 | if (blkd_state & RCU_EXP_BLKD && rdp->cpu_no_qs.b.exp) |
264 | rcu_report_exp_rdp(rdp); |
265 | else |
266 | WARN_ON_ONCE(rdp->cpu_no_qs.b.exp); |
267 | } |
268 | |
269 | /* |
270 | * Record a preemptible-RCU quiescent state for the specified CPU. |
271 | * Note that this does not necessarily mean that the task currently running |
272 | * on the CPU is in a quiescent state: Instead, it means that the current |
273 | * grace period need not wait on any RCU read-side critical section that |
274 | * starts later on this CPU. It also means that if the current task is |
275 | * in an RCU read-side critical section, it has already added itself to |
276 | * some leaf rcu_node structure's ->blkd_tasks list. In addition to the |
277 | * current task, there might be any number of other tasks blocked while |
278 | * in an RCU read-side critical section. |
279 | * |
280 | * Unlike non-preemptible-RCU, quiescent state reports for expedited |
281 | * grace periods are handled separately via deferred quiescent states |
282 | * and context switch events. |
283 | * |
284 | * Callers to this function must disable preemption. |
285 | */ |
286 | static void rcu_qs(void) |
287 | { |
288 | RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n" ); |
289 | if (__this_cpu_read(rcu_data.cpu_no_qs.b.norm)) { |
290 | trace_rcu_grace_period(TPS("rcu_preempt" ), |
291 | __this_cpu_read(rcu_data.gp_seq), |
292 | TPS("cpuqs" )); |
293 | __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false); |
294 | barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */ |
295 | WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false); |
296 | } |
297 | } |
298 | |
299 | /* |
300 | * We have entered the scheduler, and the current task might soon be |
301 | * context-switched away from. If this task is in an RCU read-side |
302 | * critical section, we will no longer be able to rely on the CPU to |
303 | * record that fact, so we enqueue the task on the blkd_tasks list. |
304 | * The task will dequeue itself when it exits the outermost enclosing |
305 | * RCU read-side critical section. Therefore, the current grace period |
306 | * cannot be permitted to complete until the blkd_tasks list entries |
307 | * predating the current grace period drain, in other words, until |
308 | * rnp->gp_tasks becomes NULL. |
309 | * |
310 | * Caller must disable interrupts. |
311 | */ |
312 | void rcu_note_context_switch(bool preempt) |
313 | { |
314 | struct task_struct *t = current; |
315 | struct rcu_data *rdp = this_cpu_ptr(&rcu_data); |
316 | struct rcu_node *rnp; |
317 | |
318 | trace_rcu_utilization(TPS("Start context switch" )); |
319 | lockdep_assert_irqs_disabled(); |
320 | WARN_ONCE(!preempt && rcu_preempt_depth() > 0, "Voluntary context switch within RCU read-side critical section!" ); |
321 | if (rcu_preempt_depth() > 0 && |
322 | !t->rcu_read_unlock_special.b.blocked) { |
323 | |
324 | /* Possibly blocking in an RCU read-side critical section. */ |
325 | rnp = rdp->mynode; |
326 | raw_spin_lock_rcu_node(rnp); |
327 | t->rcu_read_unlock_special.b.blocked = true; |
328 | t->rcu_blocked_node = rnp; |
329 | |
330 | /* |
331 | * Verify the CPU's sanity, trace the preemption, and |
332 | * then queue the task as required based on the states |
333 | * of any ongoing and expedited grace periods. |
334 | */ |
335 | WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp)); |
336 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
337 | trace_rcu_preempt_task(rcuname: rcu_state.name, |
338 | pid: t->pid, |
339 | gp_seq: (rnp->qsmask & rdp->grpmask) |
340 | ? rnp->gp_seq |
341 | : rcu_seq_snap(sp: &rnp->gp_seq)); |
342 | rcu_preempt_ctxt_queue(rnp, rdp); |
343 | } else { |
344 | rcu_preempt_deferred_qs(t); |
345 | } |
346 | |
347 | /* |
348 | * Either we were not in an RCU read-side critical section to |
349 | * begin with, or we have now recorded that critical section |
350 | * globally. Either way, we can now note a quiescent state |
351 | * for this CPU. Again, if we were in an RCU read-side critical |
352 | * section, and if that critical section was blocking the current |
353 | * grace period, then the fact that the task has been enqueued |
354 | * means that we continue to block the current grace period. |
355 | */ |
356 | rcu_qs(); |
357 | if (rdp->cpu_no_qs.b.exp) |
358 | rcu_report_exp_rdp(rdp); |
359 | rcu_tasks_qs(current, preempt); |
360 | trace_rcu_utilization(TPS("End context switch" )); |
361 | } |
362 | EXPORT_SYMBOL_GPL(rcu_note_context_switch); |
363 | |
364 | /* |
365 | * Check for preempted RCU readers blocking the current grace period |
366 | * for the specified rcu_node structure. If the caller needs a reliable |
367 | * answer, it must hold the rcu_node's ->lock. |
368 | */ |
369 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
370 | { |
371 | return READ_ONCE(rnp->gp_tasks) != NULL; |
372 | } |
373 | |
374 | /* limit value for ->rcu_read_lock_nesting. */ |
375 | #define RCU_NEST_PMAX (INT_MAX / 2) |
376 | |
377 | static void rcu_preempt_read_enter(void) |
378 | { |
379 | WRITE_ONCE(current->rcu_read_lock_nesting, READ_ONCE(current->rcu_read_lock_nesting) + 1); |
380 | } |
381 | |
382 | static int rcu_preempt_read_exit(void) |
383 | { |
384 | int ret = READ_ONCE(current->rcu_read_lock_nesting) - 1; |
385 | |
386 | WRITE_ONCE(current->rcu_read_lock_nesting, ret); |
387 | return ret; |
388 | } |
389 | |
390 | static void rcu_preempt_depth_set(int val) |
391 | { |
392 | WRITE_ONCE(current->rcu_read_lock_nesting, val); |
393 | } |
394 | |
395 | /* |
396 | * Preemptible RCU implementation for rcu_read_lock(). |
397 | * Just increment ->rcu_read_lock_nesting, shared state will be updated |
398 | * if we block. |
399 | */ |
400 | void __rcu_read_lock(void) |
401 | { |
402 | rcu_preempt_read_enter(); |
403 | if (IS_ENABLED(CONFIG_PROVE_LOCKING)) |
404 | WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX); |
405 | if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && rcu_state.gp_kthread) |
406 | WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true); |
407 | barrier(); /* critical section after entry code. */ |
408 | } |
409 | EXPORT_SYMBOL_GPL(__rcu_read_lock); |
410 | |
411 | /* |
412 | * Preemptible RCU implementation for rcu_read_unlock(). |
413 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost |
414 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then |
415 | * invoke rcu_read_unlock_special() to clean up after a context switch |
416 | * in an RCU read-side critical section and other special cases. |
417 | */ |
418 | void __rcu_read_unlock(void) |
419 | { |
420 | struct task_struct *t = current; |
421 | |
422 | barrier(); // critical section before exit code. |
423 | if (rcu_preempt_read_exit() == 0) { |
424 | barrier(); // critical-section exit before .s check. |
425 | if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) |
426 | rcu_read_unlock_special(t); |
427 | } |
428 | if (IS_ENABLED(CONFIG_PROVE_LOCKING)) { |
429 | int rrln = rcu_preempt_depth(); |
430 | |
431 | WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX); |
432 | } |
433 | } |
434 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); |
435 | |
436 | /* |
437 | * Advance a ->blkd_tasks-list pointer to the next entry, instead |
438 | * returning NULL if at the end of the list. |
439 | */ |
440 | static struct list_head *rcu_next_node_entry(struct task_struct *t, |
441 | struct rcu_node *rnp) |
442 | { |
443 | struct list_head *np; |
444 | |
445 | np = t->rcu_node_entry.next; |
446 | if (np == &rnp->blkd_tasks) |
447 | np = NULL; |
448 | return np; |
449 | } |
450 | |
451 | /* |
452 | * Return true if the specified rcu_node structure has tasks that were |
453 | * preempted within an RCU read-side critical section. |
454 | */ |
455 | static bool rcu_preempt_has_tasks(struct rcu_node *rnp) |
456 | { |
457 | return !list_empty(head: &rnp->blkd_tasks); |
458 | } |
459 | |
460 | /* |
461 | * Report deferred quiescent states. The deferral time can |
462 | * be quite short, for example, in the case of the call from |
463 | * rcu_read_unlock_special(). |
464 | */ |
465 | static notrace void |
466 | rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) |
467 | { |
468 | bool empty_exp; |
469 | bool empty_norm; |
470 | bool empty_exp_now; |
471 | struct list_head *np; |
472 | bool drop_boost_mutex = false; |
473 | struct rcu_data *rdp; |
474 | struct rcu_node *rnp; |
475 | union rcu_special special; |
476 | |
477 | /* |
478 | * If RCU core is waiting for this CPU to exit its critical section, |
479 | * report the fact that it has exited. Because irqs are disabled, |
480 | * t->rcu_read_unlock_special cannot change. |
481 | */ |
482 | special = t->rcu_read_unlock_special; |
483 | rdp = this_cpu_ptr(&rcu_data); |
484 | if (!special.s && !rdp->cpu_no_qs.b.exp) { |
485 | local_irq_restore(flags); |
486 | return; |
487 | } |
488 | t->rcu_read_unlock_special.s = 0; |
489 | if (special.b.need_qs) { |
490 | if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) { |
491 | rdp->cpu_no_qs.b.norm = false; |
492 | rcu_report_qs_rdp(rdp); |
493 | udelay(rcu_unlock_delay); |
494 | } else { |
495 | rcu_qs(); |
496 | } |
497 | } |
498 | |
499 | /* |
500 | * Respond to a request by an expedited grace period for a |
501 | * quiescent state from this CPU. Note that requests from |
502 | * tasks are handled when removing the task from the |
503 | * blocked-tasks list below. |
504 | */ |
505 | if (rdp->cpu_no_qs.b.exp) |
506 | rcu_report_exp_rdp(rdp); |
507 | |
508 | /* Clean up if blocked during RCU read-side critical section. */ |
509 | if (special.b.blocked) { |
510 | |
511 | /* |
512 | * Remove this task from the list it blocked on. The task |
513 | * now remains queued on the rcu_node corresponding to the |
514 | * CPU it first blocked on, so there is no longer any need |
515 | * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia. |
516 | */ |
517 | rnp = t->rcu_blocked_node; |
518 | raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ |
519 | WARN_ON_ONCE(rnp != t->rcu_blocked_node); |
520 | WARN_ON_ONCE(!rcu_is_leaf_node(rnp)); |
521 | empty_norm = !rcu_preempt_blocked_readers_cgp(rnp); |
522 | WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq && |
523 | (!empty_norm || rnp->qsmask)); |
524 | empty_exp = sync_rcu_exp_done(rnp); |
525 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ |
526 | np = rcu_next_node_entry(t, rnp); |
527 | list_del_init(entry: &t->rcu_node_entry); |
528 | t->rcu_blocked_node = NULL; |
529 | trace_rcu_unlock_preempted_task(TPS("rcu_preempt" ), |
530 | gp_seq: rnp->gp_seq, pid: t->pid); |
531 | if (&t->rcu_node_entry == rnp->gp_tasks) |
532 | WRITE_ONCE(rnp->gp_tasks, np); |
533 | if (&t->rcu_node_entry == rnp->exp_tasks) |
534 | WRITE_ONCE(rnp->exp_tasks, np); |
535 | if (IS_ENABLED(CONFIG_RCU_BOOST)) { |
536 | /* Snapshot ->boost_mtx ownership w/rnp->lock held. */ |
537 | drop_boost_mutex = rt_mutex_owner(lock: &rnp->boost_mtx.rtmutex) == t; |
538 | if (&t->rcu_node_entry == rnp->boost_tasks) |
539 | WRITE_ONCE(rnp->boost_tasks, np); |
540 | } |
541 | |
542 | /* |
543 | * If this was the last task on the current list, and if |
544 | * we aren't waiting on any CPUs, report the quiescent state. |
545 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, |
546 | * so we must take a snapshot of the expedited state. |
547 | */ |
548 | empty_exp_now = sync_rcu_exp_done(rnp); |
549 | if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) { |
550 | trace_rcu_quiescent_state_report(TPS("preempt_rcu" ), |
551 | gp_seq: rnp->gp_seq, |
552 | mask: 0, qsmask: rnp->qsmask, |
553 | level: rnp->level, |
554 | grplo: rnp->grplo, |
555 | grphi: rnp->grphi, |
556 | gp_tasks: !!rnp->gp_tasks); |
557 | rcu_report_unblock_qs_rnp(rnp, flags); |
558 | } else { |
559 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
560 | } |
561 | |
562 | /* |
563 | * If this was the last task on the expedited lists, |
564 | * then we need to report up the rcu_node hierarchy. |
565 | */ |
566 | if (!empty_exp && empty_exp_now) |
567 | rcu_report_exp_rnp(rnp, wake: true); |
568 | |
569 | /* Unboost if we were boosted. */ |
570 | if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) |
571 | rt_mutex_futex_unlock(lock: &rnp->boost_mtx.rtmutex); |
572 | } else { |
573 | local_irq_restore(flags); |
574 | } |
575 | } |
576 | |
577 | /* |
578 | * Is a deferred quiescent-state pending, and are we also not in |
579 | * an RCU read-side critical section? It is the caller's responsibility |
580 | * to ensure it is otherwise safe to report any deferred quiescent |
581 | * states. The reason for this is that it is safe to report a |
582 | * quiescent state during context switch even though preemption |
583 | * is disabled. This function cannot be expected to understand these |
584 | * nuances, so the caller must handle them. |
585 | */ |
586 | static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) |
587 | { |
588 | return (__this_cpu_read(rcu_data.cpu_no_qs.b.exp) || |
589 | READ_ONCE(t->rcu_read_unlock_special.s)) && |
590 | rcu_preempt_depth() == 0; |
591 | } |
592 | |
593 | /* |
594 | * Report a deferred quiescent state if needed and safe to do so. |
595 | * As with rcu_preempt_need_deferred_qs(), "safe" involves only |
596 | * not being in an RCU read-side critical section. The caller must |
597 | * evaluate safety in terms of interrupt, softirq, and preemption |
598 | * disabling. |
599 | */ |
600 | notrace void rcu_preempt_deferred_qs(struct task_struct *t) |
601 | { |
602 | unsigned long flags; |
603 | |
604 | if (!rcu_preempt_need_deferred_qs(t)) |
605 | return; |
606 | local_irq_save(flags); |
607 | rcu_preempt_deferred_qs_irqrestore(t, flags); |
608 | } |
609 | |
610 | /* |
611 | * Minimal handler to give the scheduler a chance to re-evaluate. |
612 | */ |
613 | static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp) |
614 | { |
615 | struct rcu_data *rdp; |
616 | |
617 | rdp = container_of(iwp, struct rcu_data, defer_qs_iw); |
618 | rdp->defer_qs_iw_pending = false; |
619 | } |
620 | |
621 | /* |
622 | * Handle special cases during rcu_read_unlock(), such as needing to |
623 | * notify RCU core processing or task having blocked during the RCU |
624 | * read-side critical section. |
625 | */ |
626 | static void rcu_read_unlock_special(struct task_struct *t) |
627 | { |
628 | unsigned long flags; |
629 | bool irqs_were_disabled; |
630 | bool preempt_bh_were_disabled = |
631 | !!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)); |
632 | |
633 | /* NMI handlers cannot block and cannot safely manipulate state. */ |
634 | if (in_nmi()) |
635 | return; |
636 | |
637 | local_irq_save(flags); |
638 | irqs_were_disabled = irqs_disabled_flags(flags); |
639 | if (preempt_bh_were_disabled || irqs_were_disabled) { |
640 | bool expboost; // Expedited GP in flight or possible boosting. |
641 | struct rcu_data *rdp = this_cpu_ptr(&rcu_data); |
642 | struct rcu_node *rnp = rdp->mynode; |
643 | |
644 | expboost = (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks)) || |
645 | (rdp->grpmask & READ_ONCE(rnp->expmask)) || |
646 | (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && |
647 | ((rdp->grpmask & READ_ONCE(rnp->qsmask)) || t->rcu_blocked_node)) || |
648 | (IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled && |
649 | t->rcu_blocked_node); |
650 | // Need to defer quiescent state until everything is enabled. |
651 | if (use_softirq && (in_hardirq() || (expboost && !irqs_were_disabled))) { |
652 | // Using softirq, safe to awaken, and either the |
653 | // wakeup is free or there is either an expedited |
654 | // GP in flight or a potential need to deboost. |
655 | raise_softirq_irqoff(nr: RCU_SOFTIRQ); |
656 | } else { |
657 | // Enabling BH or preempt does reschedule, so... |
658 | // Also if no expediting and no possible deboosting, |
659 | // slow is OK. Plus nohz_full CPUs eventually get |
660 | // tick enabled. |
661 | set_tsk_need_resched(current); |
662 | set_preempt_need_resched(); |
663 | if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled && |
664 | expboost && !rdp->defer_qs_iw_pending && cpu_online(cpu: rdp->cpu)) { |
665 | // Get scheduler to re-evaluate and call hooks. |
666 | // If !IRQ_WORK, FQS scan will eventually IPI. |
667 | if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && |
668 | IS_ENABLED(CONFIG_PREEMPT_RT)) |
669 | rdp->defer_qs_iw = IRQ_WORK_INIT_HARD( |
670 | rcu_preempt_deferred_qs_handler); |
671 | else |
672 | init_irq_work(work: &rdp->defer_qs_iw, |
673 | func: rcu_preempt_deferred_qs_handler); |
674 | rdp->defer_qs_iw_pending = true; |
675 | irq_work_queue_on(work: &rdp->defer_qs_iw, cpu: rdp->cpu); |
676 | } |
677 | } |
678 | local_irq_restore(flags); |
679 | return; |
680 | } |
681 | rcu_preempt_deferred_qs_irqrestore(t, flags); |
682 | } |
683 | |
684 | /* |
685 | * Check that the list of blocked tasks for the newly completed grace |
686 | * period is in fact empty. It is a serious bug to complete a grace |
687 | * period that still has RCU readers blocked! This function must be |
688 | * invoked -before- updating this rnp's ->gp_seq. |
689 | * |
690 | * Also, if there are blocked tasks on the list, they automatically |
691 | * block the newly created grace period, so set up ->gp_tasks accordingly. |
692 | */ |
693 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) |
694 | { |
695 | struct task_struct *t; |
696 | |
697 | RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n" ); |
698 | raw_lockdep_assert_held_rcu_node(rnp); |
699 | if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp))) |
700 | dump_blkd_tasks(rnp, ncheck: 10); |
701 | if (rcu_preempt_has_tasks(rnp) && |
702 | (rnp->qsmaskinit || rnp->wait_blkd_tasks)) { |
703 | WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next); |
704 | t = container_of(rnp->gp_tasks, struct task_struct, |
705 | rcu_node_entry); |
706 | trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS" ), |
707 | gp_seq: rnp->gp_seq, pid: t->pid); |
708 | } |
709 | WARN_ON_ONCE(rnp->qsmask); |
710 | } |
711 | |
712 | /* |
713 | * Check for a quiescent state from the current CPU, including voluntary |
714 | * context switches for Tasks RCU. When a task blocks, the task is |
715 | * recorded in the corresponding CPU's rcu_node structure, which is checked |
716 | * elsewhere, hence this function need only check for quiescent states |
717 | * related to the current CPU, not to those related to tasks. |
718 | */ |
719 | static void rcu_flavor_sched_clock_irq(int user) |
720 | { |
721 | struct task_struct *t = current; |
722 | |
723 | lockdep_assert_irqs_disabled(); |
724 | if (rcu_preempt_depth() > 0 || |
725 | (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) { |
726 | /* No QS, force context switch if deferred. */ |
727 | if (rcu_preempt_need_deferred_qs(t)) { |
728 | set_tsk_need_resched(t); |
729 | set_preempt_need_resched(); |
730 | } |
731 | } else if (rcu_preempt_need_deferred_qs(t)) { |
732 | rcu_preempt_deferred_qs(t); /* Report deferred QS. */ |
733 | return; |
734 | } else if (!WARN_ON_ONCE(rcu_preempt_depth())) { |
735 | rcu_qs(); /* Report immediate QS. */ |
736 | return; |
737 | } |
738 | |
739 | /* If GP is oldish, ask for help from rcu_read_unlock_special(). */ |
740 | if (rcu_preempt_depth() > 0 && |
741 | __this_cpu_read(rcu_data.core_needs_qs) && |
742 | __this_cpu_read(rcu_data.cpu_no_qs.b.norm) && |
743 | !t->rcu_read_unlock_special.b.need_qs && |
744 | time_after(jiffies, rcu_state.gp_start + HZ)) |
745 | t->rcu_read_unlock_special.b.need_qs = true; |
746 | } |
747 | |
748 | /* |
749 | * Check for a task exiting while in a preemptible-RCU read-side |
750 | * critical section, clean up if so. No need to issue warnings, as |
751 | * debug_check_no_locks_held() already does this if lockdep is enabled. |
752 | * Besides, if this function does anything other than just immediately |
753 | * return, there was a bug of some sort. Spewing warnings from this |
754 | * function is like as not to simply obscure important prior warnings. |
755 | */ |
756 | void exit_rcu(void) |
757 | { |
758 | struct task_struct *t = current; |
759 | |
760 | if (unlikely(!list_empty(¤t->rcu_node_entry))) { |
761 | rcu_preempt_depth_set(val: 1); |
762 | barrier(); |
763 | WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true); |
764 | } else if (unlikely(rcu_preempt_depth())) { |
765 | rcu_preempt_depth_set(val: 1); |
766 | } else { |
767 | return; |
768 | } |
769 | __rcu_read_unlock(); |
770 | rcu_preempt_deferred_qs(current); |
771 | } |
772 | |
773 | /* |
774 | * Dump the blocked-tasks state, but limit the list dump to the |
775 | * specified number of elements. |
776 | */ |
777 | static void |
778 | dump_blkd_tasks(struct rcu_node *rnp, int ncheck) |
779 | { |
780 | int cpu; |
781 | int i; |
782 | struct list_head *lhp; |
783 | struct rcu_data *rdp; |
784 | struct rcu_node *rnp1; |
785 | |
786 | raw_lockdep_assert_held_rcu_node(rnp); |
787 | pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n" , |
788 | __func__, rnp->grplo, rnp->grphi, rnp->level, |
789 | (long)READ_ONCE(rnp->gp_seq), (long)rnp->completedqs); |
790 | for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent) |
791 | pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n" , |
792 | __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext); |
793 | pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n" , |
794 | __func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks), |
795 | READ_ONCE(rnp->exp_tasks)); |
796 | pr_info("%s: ->blkd_tasks" , __func__); |
797 | i = 0; |
798 | list_for_each(lhp, &rnp->blkd_tasks) { |
799 | pr_cont(" %p" , lhp); |
800 | if (++i >= ncheck) |
801 | break; |
802 | } |
803 | pr_cont("\n" ); |
804 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) { |
805 | rdp = per_cpu_ptr(&rcu_data, cpu); |
806 | pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n" , |
807 | cpu, ".o" [rcu_rdp_cpu_online(rdp)], |
808 | (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags, |
809 | (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags); |
810 | } |
811 | } |
812 | |
813 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
814 | |
815 | /* |
816 | * If strict grace periods are enabled, and if the calling |
817 | * __rcu_read_unlock() marks the beginning of a quiescent state, immediately |
818 | * report that quiescent state and, if requested, spin for a bit. |
819 | */ |
820 | void rcu_read_unlock_strict(void) |
821 | { |
822 | struct rcu_data *rdp; |
823 | |
824 | if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread) |
825 | return; |
826 | rdp = this_cpu_ptr(&rcu_data); |
827 | rdp->cpu_no_qs.b.norm = false; |
828 | rcu_report_qs_rdp(rdp); |
829 | udelay(rcu_unlock_delay); |
830 | } |
831 | EXPORT_SYMBOL_GPL(rcu_read_unlock_strict); |
832 | |
833 | /* |
834 | * Tell them what RCU they are running. |
835 | */ |
836 | static void __init rcu_bootup_announce(void) |
837 | { |
838 | pr_info("Hierarchical RCU implementation.\n" ); |
839 | rcu_bootup_announce_oddness(); |
840 | } |
841 | |
842 | /* |
843 | * Note a quiescent state for PREEMPTION=n. Because we do not need to know |
844 | * how many quiescent states passed, just if there was at least one since |
845 | * the start of the grace period, this just sets a flag. The caller must |
846 | * have disabled preemption. |
847 | */ |
848 | static void rcu_qs(void) |
849 | { |
850 | RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!" ); |
851 | if (!__this_cpu_read(rcu_data.cpu_no_qs.s)) |
852 | return; |
853 | trace_rcu_grace_period(TPS("rcu_sched" ), |
854 | __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs" )); |
855 | __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false); |
856 | if (__this_cpu_read(rcu_data.cpu_no_qs.b.exp)) |
857 | rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); |
858 | } |
859 | |
860 | /* |
861 | * Register an urgently needed quiescent state. If there is an |
862 | * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight |
863 | * dyntick-idle quiescent state visible to other CPUs, which will in |
864 | * some cases serve for expedited as well as normal grace periods. |
865 | * Either way, register a lightweight quiescent state. |
866 | */ |
867 | void rcu_all_qs(void) |
868 | { |
869 | unsigned long flags; |
870 | |
871 | if (!raw_cpu_read(rcu_data.rcu_urgent_qs)) |
872 | return; |
873 | preempt_disable(); // For CONFIG_PREEMPT_COUNT=y kernels |
874 | /* Load rcu_urgent_qs before other flags. */ |
875 | if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) { |
876 | preempt_enable(); |
877 | return; |
878 | } |
879 | this_cpu_write(rcu_data.rcu_urgent_qs, false); |
880 | if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) { |
881 | local_irq_save(flags); |
882 | rcu_momentary_dyntick_idle(); |
883 | local_irq_restore(flags); |
884 | } |
885 | rcu_qs(); |
886 | preempt_enable(); |
887 | } |
888 | EXPORT_SYMBOL_GPL(rcu_all_qs); |
889 | |
890 | /* |
891 | * Note a PREEMPTION=n context switch. The caller must have disabled interrupts. |
892 | */ |
893 | void rcu_note_context_switch(bool preempt) |
894 | { |
895 | trace_rcu_utilization(TPS("Start context switch" )); |
896 | rcu_qs(); |
897 | /* Load rcu_urgent_qs before other flags. */ |
898 | if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) |
899 | goto out; |
900 | this_cpu_write(rcu_data.rcu_urgent_qs, false); |
901 | if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) |
902 | rcu_momentary_dyntick_idle(); |
903 | out: |
904 | rcu_tasks_qs(current, preempt); |
905 | trace_rcu_utilization(TPS("End context switch" )); |
906 | } |
907 | EXPORT_SYMBOL_GPL(rcu_note_context_switch); |
908 | |
909 | /* |
910 | * Because preemptible RCU does not exist, there are never any preempted |
911 | * RCU readers. |
912 | */ |
913 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
914 | { |
915 | return 0; |
916 | } |
917 | |
918 | /* |
919 | * Because there is no preemptible RCU, there can be no readers blocked. |
920 | */ |
921 | static bool rcu_preempt_has_tasks(struct rcu_node *rnp) |
922 | { |
923 | return false; |
924 | } |
925 | |
926 | /* |
927 | * Because there is no preemptible RCU, there can be no deferred quiescent |
928 | * states. |
929 | */ |
930 | static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) |
931 | { |
932 | return false; |
933 | } |
934 | |
935 | // Except that we do need to respond to a request by an expedited |
936 | // grace period for a quiescent state from this CPU. Note that in |
937 | // non-preemptible kernels, there can be no context switches within RCU |
938 | // read-side critical sections, which in turn means that the leaf rcu_node |
939 | // structure's blocked-tasks list is always empty. is therefore no need to |
940 | // actually check it. Instead, a quiescent state from this CPU suffices, |
941 | // and this function is only called from such a quiescent state. |
942 | notrace void rcu_preempt_deferred_qs(struct task_struct *t) |
943 | { |
944 | struct rcu_data *rdp = this_cpu_ptr(&rcu_data); |
945 | |
946 | if (READ_ONCE(rdp->cpu_no_qs.b.exp)) |
947 | rcu_report_exp_rdp(rdp); |
948 | } |
949 | |
950 | /* |
951 | * Because there is no preemptible RCU, there can be no readers blocked, |
952 | * so there is no need to check for blocked tasks. So check only for |
953 | * bogus qsmask values. |
954 | */ |
955 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) |
956 | { |
957 | WARN_ON_ONCE(rnp->qsmask); |
958 | } |
959 | |
960 | /* |
961 | * Check to see if this CPU is in a non-context-switch quiescent state, |
962 | * namely user mode and idle loop. |
963 | */ |
964 | static void rcu_flavor_sched_clock_irq(int user) |
965 | { |
966 | if (user || rcu_is_cpu_rrupt_from_idle()) { |
967 | |
968 | /* |
969 | * Get here if this CPU took its interrupt from user |
970 | * mode or from the idle loop, and if this is not a |
971 | * nested interrupt. In this case, the CPU is in |
972 | * a quiescent state, so note it. |
973 | * |
974 | * No memory barrier is required here because rcu_qs() |
975 | * references only CPU-local variables that other CPUs |
976 | * neither access nor modify, at least not while the |
977 | * corresponding CPU is online. |
978 | */ |
979 | rcu_qs(); |
980 | } |
981 | } |
982 | |
983 | /* |
984 | * Because preemptible RCU does not exist, tasks cannot possibly exit |
985 | * while in preemptible RCU read-side critical sections. |
986 | */ |
987 | void exit_rcu(void) |
988 | { |
989 | } |
990 | |
991 | /* |
992 | * Dump the guaranteed-empty blocked-tasks state. Trust but verify. |
993 | */ |
994 | static void |
995 | dump_blkd_tasks(struct rcu_node *rnp, int ncheck) |
996 | { |
997 | WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks)); |
998 | } |
999 | |
1000 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
1001 | |
1002 | /* |
1003 | * If boosting, set rcuc kthreads to realtime priority. |
1004 | */ |
1005 | static void rcu_cpu_kthread_setup(unsigned int cpu) |
1006 | { |
1007 | struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); |
1008 | #ifdef CONFIG_RCU_BOOST |
1009 | struct sched_param sp; |
1010 | |
1011 | sp.sched_priority = kthread_prio; |
1012 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); |
1013 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
1014 | |
1015 | WRITE_ONCE(rdp->rcuc_activity, jiffies); |
1016 | } |
1017 | |
1018 | static bool rcu_is_callbacks_nocb_kthread(struct rcu_data *rdp) |
1019 | { |
1020 | #ifdef CONFIG_RCU_NOCB_CPU |
1021 | return rdp->nocb_cb_kthread == current; |
1022 | #else |
1023 | return false; |
1024 | #endif |
1025 | } |
1026 | |
1027 | /* |
1028 | * Is the current CPU running the RCU-callbacks kthread? |
1029 | * Caller must have preemption disabled. |
1030 | */ |
1031 | static bool rcu_is_callbacks_kthread(struct rcu_data *rdp) |
1032 | { |
1033 | return rdp->rcu_cpu_kthread_task == current || |
1034 | rcu_is_callbacks_nocb_kthread(rdp); |
1035 | } |
1036 | |
1037 | #ifdef CONFIG_RCU_BOOST |
1038 | |
1039 | /* |
1040 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks |
1041 | * or ->boost_tasks, advancing the pointer to the next task in the |
1042 | * ->blkd_tasks list. |
1043 | * |
1044 | * Note that irqs must be enabled: boosting the task can block. |
1045 | * Returns 1 if there are more tasks needing to be boosted. |
1046 | */ |
1047 | static int rcu_boost(struct rcu_node *rnp) |
1048 | { |
1049 | unsigned long flags; |
1050 | struct task_struct *t; |
1051 | struct list_head *tb; |
1052 | |
1053 | if (READ_ONCE(rnp->exp_tasks) == NULL && |
1054 | READ_ONCE(rnp->boost_tasks) == NULL) |
1055 | return 0; /* Nothing left to boost. */ |
1056 | |
1057 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
1058 | |
1059 | /* |
1060 | * Recheck under the lock: all tasks in need of boosting |
1061 | * might exit their RCU read-side critical sections on their own. |
1062 | */ |
1063 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { |
1064 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
1065 | return 0; |
1066 | } |
1067 | |
1068 | /* |
1069 | * Preferentially boost tasks blocking expedited grace periods. |
1070 | * This cannot starve the normal grace periods because a second |
1071 | * expedited grace period must boost all blocked tasks, including |
1072 | * those blocking the pre-existing normal grace period. |
1073 | */ |
1074 | if (rnp->exp_tasks != NULL) |
1075 | tb = rnp->exp_tasks; |
1076 | else |
1077 | tb = rnp->boost_tasks; |
1078 | |
1079 | /* |
1080 | * We boost task t by manufacturing an rt_mutex that appears to |
1081 | * be held by task t. We leave a pointer to that rt_mutex where |
1082 | * task t can find it, and task t will release the mutex when it |
1083 | * exits its outermost RCU read-side critical section. Then |
1084 | * simply acquiring this artificial rt_mutex will boost task |
1085 | * t's priority. (Thanks to tglx for suggesting this approach!) |
1086 | * |
1087 | * Note that task t must acquire rnp->lock to remove itself from |
1088 | * the ->blkd_tasks list, which it will do from exit() if from |
1089 | * nowhere else. We therefore are guaranteed that task t will |
1090 | * stay around at least until we drop rnp->lock. Note that |
1091 | * rnp->lock also resolves races between our priority boosting |
1092 | * and task t's exiting its outermost RCU read-side critical |
1093 | * section. |
1094 | */ |
1095 | t = container_of(tb, struct task_struct, rcu_node_entry); |
1096 | rt_mutex_init_proxy_locked(lock: &rnp->boost_mtx.rtmutex, proxy_owner: t); |
1097 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
1098 | /* Lock only for side effect: boosts task t's priority. */ |
1099 | rt_mutex_lock(&rnp->boost_mtx); |
1100 | rt_mutex_unlock(lock: &rnp->boost_mtx); /* Then keep lockdep happy. */ |
1101 | rnp->n_boosts++; |
1102 | |
1103 | return READ_ONCE(rnp->exp_tasks) != NULL || |
1104 | READ_ONCE(rnp->boost_tasks) != NULL; |
1105 | } |
1106 | |
1107 | /* |
1108 | * Priority-boosting kthread, one per leaf rcu_node. |
1109 | */ |
1110 | static int rcu_boost_kthread(void *arg) |
1111 | { |
1112 | struct rcu_node *rnp = (struct rcu_node *)arg; |
1113 | int spincnt = 0; |
1114 | int more2boost; |
1115 | |
1116 | trace_rcu_utilization(TPS("Start boost kthread@init" )); |
1117 | for (;;) { |
1118 | WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING); |
1119 | trace_rcu_utilization(TPS("End boost kthread@rcu_wait" )); |
1120 | rcu_wait(READ_ONCE(rnp->boost_tasks) || |
1121 | READ_ONCE(rnp->exp_tasks)); |
1122 | trace_rcu_utilization(TPS("Start boost kthread@rcu_wait" )); |
1123 | WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING); |
1124 | more2boost = rcu_boost(rnp); |
1125 | if (more2boost) |
1126 | spincnt++; |
1127 | else |
1128 | spincnt = 0; |
1129 | if (spincnt > 10) { |
1130 | WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING); |
1131 | trace_rcu_utilization(TPS("End boost kthread@rcu_yield" )); |
1132 | schedule_timeout_idle(timeout: 2); |
1133 | trace_rcu_utilization(TPS("Start boost kthread@rcu_yield" )); |
1134 | spincnt = 0; |
1135 | } |
1136 | } |
1137 | /* NOTREACHED */ |
1138 | trace_rcu_utilization(TPS("End boost kthread@notreached" )); |
1139 | return 0; |
1140 | } |
1141 | |
1142 | /* |
1143 | * Check to see if it is time to start boosting RCU readers that are |
1144 | * blocking the current grace period, and, if so, tell the per-rcu_node |
1145 | * kthread to start boosting them. If there is an expedited grace |
1146 | * period in progress, it is always time to boost. |
1147 | * |
1148 | * The caller must hold rnp->lock, which this function releases. |
1149 | * The ->boost_kthread_task is immortal, so we don't need to worry |
1150 | * about it going away. |
1151 | */ |
1152 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
1153 | __releases(rnp->lock) |
1154 | { |
1155 | raw_lockdep_assert_held_rcu_node(rnp); |
1156 | if (!rnp->boost_kthread_task || |
1157 | (!rcu_preempt_blocked_readers_cgp(rnp) && !rnp->exp_tasks)) { |
1158 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
1159 | return; |
1160 | } |
1161 | if (rnp->exp_tasks != NULL || |
1162 | (rnp->gp_tasks != NULL && |
1163 | rnp->boost_tasks == NULL && |
1164 | rnp->qsmask == 0 && |
1165 | (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld || |
1166 | IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)))) { |
1167 | if (rnp->exp_tasks == NULL) |
1168 | WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks); |
1169 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
1170 | rcu_wake_cond(t: rnp->boost_kthread_task, |
1171 | READ_ONCE(rnp->boost_kthread_status)); |
1172 | } else { |
1173 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
1174 | } |
1175 | } |
1176 | |
1177 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
1178 | |
1179 | /* |
1180 | * Do priority-boost accounting for the start of a new grace period. |
1181 | */ |
1182 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1183 | { |
1184 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; |
1185 | } |
1186 | |
1187 | /* |
1188 | * Create an RCU-boost kthread for the specified node if one does not |
1189 | * already exist. We only create this kthread for preemptible RCU. |
1190 | */ |
1191 | static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) |
1192 | { |
1193 | unsigned long flags; |
1194 | int rnp_index = rnp - rcu_get_root(); |
1195 | struct sched_param sp; |
1196 | struct task_struct *t; |
1197 | |
1198 | mutex_lock(&rnp->boost_kthread_mutex); |
1199 | if (rnp->boost_kthread_task || !rcu_scheduler_fully_active) |
1200 | goto out; |
1201 | |
1202 | t = kthread_create(rcu_boost_kthread, (void *)rnp, |
1203 | "rcub/%d" , rnp_index); |
1204 | if (WARN_ON_ONCE(IS_ERR(t))) |
1205 | goto out; |
1206 | |
1207 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
1208 | rnp->boost_kthread_task = t; |
1209 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
1210 | sp.sched_priority = kthread_prio; |
1211 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
1212 | wake_up_process(tsk: t); /* get to TASK_INTERRUPTIBLE quickly. */ |
1213 | |
1214 | out: |
1215 | mutex_unlock(lock: &rnp->boost_kthread_mutex); |
1216 | } |
1217 | |
1218 | /* |
1219 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are |
1220 | * served by the rcu_node in question. The CPU hotplug lock is still |
1221 | * held, so the value of rnp->qsmaskinit will be stable. |
1222 | * |
1223 | * We don't include outgoingcpu in the affinity set, use -1 if there is |
1224 | * no outgoing CPU. If there are no CPUs left in the affinity set, |
1225 | * this function allows the kthread to execute on any CPU. |
1226 | * |
1227 | * Any future concurrent calls are serialized via ->boost_kthread_mutex. |
1228 | */ |
1229 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
1230 | { |
1231 | struct task_struct *t = rnp->boost_kthread_task; |
1232 | unsigned long mask; |
1233 | cpumask_var_t cm; |
1234 | int cpu; |
1235 | |
1236 | if (!t) |
1237 | return; |
1238 | if (!zalloc_cpumask_var(mask: &cm, GFP_KERNEL)) |
1239 | return; |
1240 | mutex_lock(&rnp->boost_kthread_mutex); |
1241 | mask = rcu_rnp_online_cpus(rnp); |
1242 | for_each_leaf_node_possible_cpu(rnp, cpu) |
1243 | if ((mask & leaf_node_cpu_bit(rnp, cpu)) && |
1244 | cpu != outgoingcpu) |
1245 | cpumask_set_cpu(cpu, dstp: cm); |
1246 | cpumask_and(dstp: cm, src1p: cm, src2p: housekeeping_cpumask(type: HK_TYPE_RCU)); |
1247 | if (cpumask_empty(srcp: cm)) { |
1248 | cpumask_copy(dstp: cm, srcp: housekeeping_cpumask(type: HK_TYPE_RCU)); |
1249 | if (outgoingcpu >= 0) |
1250 | cpumask_clear_cpu(cpu: outgoingcpu, dstp: cm); |
1251 | } |
1252 | set_cpus_allowed_ptr(p: t, new_mask: cm); |
1253 | mutex_unlock(lock: &rnp->boost_kthread_mutex); |
1254 | free_cpumask_var(mask: cm); |
1255 | } |
1256 | |
1257 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1258 | |
1259 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
1260 | __releases(rnp->lock) |
1261 | { |
1262 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
1263 | } |
1264 | |
1265 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1266 | { |
1267 | } |
1268 | |
1269 | static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) |
1270 | { |
1271 | } |
1272 | |
1273 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
1274 | { |
1275 | } |
1276 | |
1277 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1278 | |
1279 | /* |
1280 | * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the |
1281 | * grace-period kthread will do force_quiescent_state() processing? |
1282 | * The idea is to avoid waking up RCU core processing on such a |
1283 | * CPU unless the grace period has extended for too long. |
1284 | * |
1285 | * This code relies on the fact that all NO_HZ_FULL CPUs are also |
1286 | * RCU_NOCB_CPU CPUs. |
1287 | */ |
1288 | static bool rcu_nohz_full_cpu(void) |
1289 | { |
1290 | #ifdef CONFIG_NO_HZ_FULL |
1291 | if (tick_nohz_full_cpu(smp_processor_id()) && |
1292 | (!rcu_gp_in_progress() || |
1293 | time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ))) |
1294 | return true; |
1295 | #endif /* #ifdef CONFIG_NO_HZ_FULL */ |
1296 | return false; |
1297 | } |
1298 | |
1299 | /* |
1300 | * Bind the RCU grace-period kthreads to the housekeeping CPU. |
1301 | */ |
1302 | static void rcu_bind_gp_kthread(void) |
1303 | { |
1304 | if (!tick_nohz_full_enabled()) |
1305 | return; |
1306 | housekeeping_affine(current, type: HK_TYPE_RCU); |
1307 | } |
1308 | |