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// SPDX-License-Identifier: GPL-2.0-or-later
* Copyright (C) 2022-2023 Oracle. All Rights Reserved.
* Author: Darrick J. Wong <>
#ifndef XFS_DRAIN_H_
#define XFS_DRAIN_H_
struct xfs_perag;
* Passive drain mechanism. This data structure tracks a count of some items
* and contains a waitqueue for callers who would like to wake up when the
* count hits zero.
struct xfs_defer_drain {
/* Number of items pending in some part of the filesystem. */
atomic_t dr_count;
/* Queue to wait for dri_count to go to zero */
struct wait_queue_head dr_waiters;
void xfs_defer_drain_init(struct xfs_defer_drain *dr);
void xfs_defer_drain_free(struct xfs_defer_drain *dr);
void xfs_drain_wait_disable(void);
void xfs_drain_wait_enable(void);
* Deferred Work Intent Drains
* ===========================
* When a writer thread executes a chain of log intent items, the AG header
* buffer locks will cycle during a transaction roll to get from one intent
* item to the next in a chain. Although scrub takes all AG header buffer
* locks, this isn't sufficient to guard against scrub checking an AG while
* that writer thread is in the middle of finishing a chain because there's no
* higher level locking primitive guarding allocation groups.
* When there's a collision, cross-referencing between data structures (e.g.
* rmapbt and refcountbt) yields false corruption events; if repair is running,
* this results in incorrect repairs, which is catastrophic.
* The solution is to the perag structure the count of active intents and make
* scrub wait until it has both AG header buffer locks and the intent counter
* reaches zero. It is therefore critical that deferred work threads hold the
* AGI or AGF buffers when decrementing the intent counter.
* Given a list of deferred work items, the deferred work manager will complete
* a work item and all the sub-items that the parent item creates before moving
* on to the next work item in the list. This is also true for all levels of
* sub-items. Writer threads are permitted to queue multiple work items
* targetting the same AG, so a deferred work item (such as a BUI) that creates
* sub-items (such as RUIs) must bump the intent counter and maintain it until
* the sub-items can themselves bump the intent counter.
* Therefore, the intent count tracks entire lifetimes of deferred work items.
* All functions that create work items must increment the intent counter as
* soon as the item is added to the transaction and cannot drop the counter
* until the item is finished or cancelled.
struct xfs_perag *xfs_perag_intent_get(struct xfs_mount *mp,
xfs_agnumber_t agno);
void xfs_perag_intent_put(struct xfs_perag *pag);
void xfs_perag_intent_hold(struct xfs_perag *pag);
void xfs_perag_intent_rele(struct xfs_perag *pag);
int xfs_perag_intent_drain(struct xfs_perag *pag);
bool xfs_perag_intent_busy(struct xfs_perag *pag);
struct xfs_defer_drain { /* empty */ };
#define xfs_defer_drain_free(dr) ((void)0)
#define xfs_defer_drain_init(dr) ((void)0)
#define xfs_perag_intent_get(mp, agno) xfs_perag_get((mp), (agno))
#define xfs_perag_intent_put(pag) xfs_perag_put(pag)
static inline void xfs_perag_intent_hold(struct xfs_perag *pag) { }
static inline void xfs_perag_intent_rele(struct xfs_perag *pag) { }
#endif /* XFS_DRAIN_H_ */