1 | // SPDX-License-Identifier: GPL-2.0-or-later |
2 | /* |
3 | * Copyright (C) 2022-2023 Oracle. All Rights Reserved. |
4 | * Author: Darrick J. Wong <djwong@kernel.org> |
5 | */ |
6 | #ifndef XFS_DRAIN_H_ |
7 | #define XFS_DRAIN_H_ |
8 | |
9 | struct xfs_perag; |
10 | |
11 | #ifdef CONFIG_XFS_DRAIN_INTENTS |
12 | /* |
13 | * Passive drain mechanism. This data structure tracks a count of some items |
14 | * and contains a waitqueue for callers who would like to wake up when the |
15 | * count hits zero. |
16 | */ |
17 | struct xfs_defer_drain { |
18 | /* Number of items pending in some part of the filesystem. */ |
19 | atomic_t dr_count; |
20 | |
21 | /* Queue to wait for dri_count to go to zero */ |
22 | struct wait_queue_head dr_waiters; |
23 | }; |
24 | |
25 | void xfs_defer_drain_init(struct xfs_defer_drain *dr); |
26 | void xfs_defer_drain_free(struct xfs_defer_drain *dr); |
27 | |
28 | void xfs_drain_wait_disable(void); |
29 | void xfs_drain_wait_enable(void); |
30 | |
31 | /* |
32 | * Deferred Work Intent Drains |
33 | * =========================== |
34 | * |
35 | * When a writer thread executes a chain of log intent items, the AG header |
36 | * buffer locks will cycle during a transaction roll to get from one intent |
37 | * item to the next in a chain. Although scrub takes all AG header buffer |
38 | * locks, this isn't sufficient to guard against scrub checking an AG while |
39 | * that writer thread is in the middle of finishing a chain because there's no |
40 | * higher level locking primitive guarding allocation groups. |
41 | * |
42 | * When there's a collision, cross-referencing between data structures (e.g. |
43 | * rmapbt and refcountbt) yields false corruption events; if repair is running, |
44 | * this results in incorrect repairs, which is catastrophic. |
45 | * |
46 | * The solution is to the perag structure the count of active intents and make |
47 | * scrub wait until it has both AG header buffer locks and the intent counter |
48 | * reaches zero. It is therefore critical that deferred work threads hold the |
49 | * AGI or AGF buffers when decrementing the intent counter. |
50 | * |
51 | * Given a list of deferred work items, the deferred work manager will complete |
52 | * a work item and all the sub-items that the parent item creates before moving |
53 | * on to the next work item in the list. This is also true for all levels of |
54 | * sub-items. Writer threads are permitted to queue multiple work items |
55 | * targetting the same AG, so a deferred work item (such as a BUI) that creates |
56 | * sub-items (such as RUIs) must bump the intent counter and maintain it until |
57 | * the sub-items can themselves bump the intent counter. |
58 | * |
59 | * Therefore, the intent count tracks entire lifetimes of deferred work items. |
60 | * All functions that create work items must increment the intent counter as |
61 | * soon as the item is added to the transaction and cannot drop the counter |
62 | * until the item is finished or cancelled. |
63 | */ |
64 | struct xfs_perag *xfs_perag_intent_get(struct xfs_mount *mp, |
65 | xfs_agnumber_t agno); |
66 | void xfs_perag_intent_put(struct xfs_perag *pag); |
67 | |
68 | void xfs_perag_intent_hold(struct xfs_perag *pag); |
69 | void xfs_perag_intent_rele(struct xfs_perag *pag); |
70 | |
71 | int xfs_perag_intent_drain(struct xfs_perag *pag); |
72 | bool xfs_perag_intent_busy(struct xfs_perag *pag); |
73 | #else |
74 | struct xfs_defer_drain { /* empty */ }; |
75 | |
76 | #define xfs_defer_drain_free(dr) ((void)0) |
77 | #define xfs_defer_drain_init(dr) ((void)0) |
78 | |
79 | #define xfs_perag_intent_get(mp, agno) xfs_perag_get((mp), (agno)) |
80 | #define xfs_perag_intent_put(pag) xfs_perag_put(pag) |
81 | |
82 | static inline void xfs_perag_intent_hold(struct xfs_perag *pag) { } |
83 | static inline void xfs_perag_intent_rele(struct xfs_perag *pag) { } |
84 | |
85 | #endif /* CONFIG_XFS_DRAIN_INTENTS */ |
86 | |
87 | #endif /* XFS_DRAIN_H_ */ |
88 | |