1d5c88131SDarrick J. Wong // SPDX-License-Identifier: GPL-2.0-or-later
2d5c88131SDarrick J. Wong /*
3d5c88131SDarrick J. Wong * Copyright (C) 2022-2023 Oracle. All Rights Reserved.
4d5c88131SDarrick J. Wong * Author: Darrick J. Wong <djwong@kernel.org>
5d5c88131SDarrick J. Wong */
6d5c88131SDarrick J. Wong #ifndef XFS_DRAIN_H_
7d5c88131SDarrick J. Wong #define XFS_DRAIN_H_
8d5c88131SDarrick J. Wong
9d5c88131SDarrick J. Wong struct xfs_perag;
10d5c88131SDarrick J. Wong
11d5c88131SDarrick J. Wong #ifdef CONFIG_XFS_DRAIN_INTENTS
12d5c88131SDarrick J. Wong /*
13d5c88131SDarrick J. Wong * Passive drain mechanism. This data structure tracks a count of some items
14d5c88131SDarrick J. Wong * and contains a waitqueue for callers who would like to wake up when the
15d5c88131SDarrick J. Wong * count hits zero.
16d5c88131SDarrick J. Wong */
17d5c88131SDarrick J. Wong struct xfs_defer_drain {
18d5c88131SDarrick J. Wong /* Number of items pending in some part of the filesystem. */
19d5c88131SDarrick J. Wong atomic_t dr_count;
20d5c88131SDarrick J. Wong
21d5c88131SDarrick J. Wong /* Queue to wait for dri_count to go to zero */
22d5c88131SDarrick J. Wong struct wait_queue_head dr_waiters;
23d5c88131SDarrick J. Wong };
24d5c88131SDarrick J. Wong
25d5c88131SDarrick J. Wong void xfs_defer_drain_init(struct xfs_defer_drain *dr);
26d5c88131SDarrick J. Wong void xfs_defer_drain_free(struct xfs_defer_drain *dr);
27d5c88131SDarrick J. Wong
28*466c525dSDarrick J. Wong void xfs_drain_wait_disable(void);
29*466c525dSDarrick J. Wong void xfs_drain_wait_enable(void);
30*466c525dSDarrick J. Wong
31d5c88131SDarrick J. Wong /*
32d5c88131SDarrick J. Wong * Deferred Work Intent Drains
33d5c88131SDarrick J. Wong * ===========================
34d5c88131SDarrick J. Wong *
35d5c88131SDarrick J. Wong * When a writer thread executes a chain of log intent items, the AG header
36d5c88131SDarrick J. Wong * buffer locks will cycle during a transaction roll to get from one intent
37d5c88131SDarrick J. Wong * item to the next in a chain. Although scrub takes all AG header buffer
38d5c88131SDarrick J. Wong * locks, this isn't sufficient to guard against scrub checking an AG while
39d5c88131SDarrick J. Wong * that writer thread is in the middle of finishing a chain because there's no
40d5c88131SDarrick J. Wong * higher level locking primitive guarding allocation groups.
41d5c88131SDarrick J. Wong *
42d5c88131SDarrick J. Wong * When there's a collision, cross-referencing between data structures (e.g.
43d5c88131SDarrick J. Wong * rmapbt and refcountbt) yields false corruption events; if repair is running,
44d5c88131SDarrick J. Wong * this results in incorrect repairs, which is catastrophic.
45d5c88131SDarrick J. Wong *
46d5c88131SDarrick J. Wong * The solution is to the perag structure the count of active intents and make
47d5c88131SDarrick J. Wong * scrub wait until it has both AG header buffer locks and the intent counter
48d5c88131SDarrick J. Wong * reaches zero. It is therefore critical that deferred work threads hold the
49d5c88131SDarrick J. Wong * AGI or AGF buffers when decrementing the intent counter.
50d5c88131SDarrick J. Wong *
51d5c88131SDarrick J. Wong * Given a list of deferred work items, the deferred work manager will complete
52d5c88131SDarrick J. Wong * a work item and all the sub-items that the parent item creates before moving
53d5c88131SDarrick J. Wong * on to the next work item in the list. This is also true for all levels of
54d5c88131SDarrick J. Wong * sub-items. Writer threads are permitted to queue multiple work items
55d5c88131SDarrick J. Wong * targetting the same AG, so a deferred work item (such as a BUI) that creates
56d5c88131SDarrick J. Wong * sub-items (such as RUIs) must bump the intent counter and maintain it until
57d5c88131SDarrick J. Wong * the sub-items can themselves bump the intent counter.
58d5c88131SDarrick J. Wong *
59d5c88131SDarrick J. Wong * Therefore, the intent count tracks entire lifetimes of deferred work items.
60d5c88131SDarrick J. Wong * All functions that create work items must increment the intent counter as
61d5c88131SDarrick J. Wong * soon as the item is added to the transaction and cannot drop the counter
62d5c88131SDarrick J. Wong * until the item is finished or cancelled.
63d5c88131SDarrick J. Wong */
64d5c88131SDarrick J. Wong struct xfs_perag *xfs_perag_intent_get(struct xfs_mount *mp,
65d5c88131SDarrick J. Wong xfs_agnumber_t agno);
66d5c88131SDarrick J. Wong void xfs_perag_intent_put(struct xfs_perag *pag);
67d5c88131SDarrick J. Wong
68d5c88131SDarrick J. Wong void xfs_perag_intent_hold(struct xfs_perag *pag);
69d5c88131SDarrick J. Wong void xfs_perag_intent_rele(struct xfs_perag *pag);
70d5c88131SDarrick J. Wong
71d5c88131SDarrick J. Wong int xfs_perag_intent_drain(struct xfs_perag *pag);
72d5c88131SDarrick J. Wong bool xfs_perag_intent_busy(struct xfs_perag *pag);
73d5c88131SDarrick J. Wong #else
74d5c88131SDarrick J. Wong struct xfs_defer_drain { /* empty */ };
75d5c88131SDarrick J. Wong
76d5c88131SDarrick J. Wong #define xfs_defer_drain_free(dr) ((void)0)
77d5c88131SDarrick J. Wong #define xfs_defer_drain_init(dr) ((void)0)
78d5c88131SDarrick J. Wong
79d5c88131SDarrick J. Wong #define xfs_perag_intent_get(mp, agno) xfs_perag_get((mp), (agno))
80d5c88131SDarrick J. Wong #define xfs_perag_intent_put(pag) xfs_perag_put(pag)
81d5c88131SDarrick J. Wong
xfs_perag_intent_hold(struct xfs_perag * pag)82d5c88131SDarrick J. Wong static inline void xfs_perag_intent_hold(struct xfs_perag *pag) { }
xfs_perag_intent_rele(struct xfs_perag * pag)83d5c88131SDarrick J. Wong static inline void xfs_perag_intent_rele(struct xfs_perag *pag) { }
84d5c88131SDarrick J. Wong
85d5c88131SDarrick J. Wong #endif /* CONFIG_XFS_DRAIN_INTENTS */
86d5c88131SDarrick J. Wong
87d5c88131SDarrick J. Wong #endif /* XFS_DRAIN_H_ */
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