fs/xfs/xfs_drain.h

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