xfs_drain.c

  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#include "xfs.h"
  7#include "xfs_fs.h"
  8#include "xfs_shared.h"
  9#include "xfs_format.h"
 10#include "xfs_trans_resv.h"
 11#include "xfs_mount.h"
 12#include "xfs_ag.h"
 13#include "xfs_trace.h"
 14
 15/*
 16 * Use a static key here to reduce the overhead of xfs_defer_drain_rele.  If
 17 * the compiler supports jump labels, the static branch will be replaced by a
 18 * nop sled when there are no xfs_defer_drain_wait callers.  Online fsck is
 19 * currently the only caller, so this is a reasonable tradeoff.
 20 *
 21 * Note: Patching the kernel code requires taking the cpu hotplug lock.  Other
 22 * parts of the kernel allocate memory with that lock held, which means that
 23 * XFS callers cannot hold any locks that might be used by memory reclaim or
 24 * writeback when calling the static_branch_{inc,dec} functions.
 25 */
 26static DEFINE_STATIC_KEY_FALSE(xfs_defer_drain_waiter_gate);
 27
 28void
 29xfs_defer_drain_wait_disable(void)
 30{
 31	static_branch_dec(&xfs_defer_drain_waiter_gate);
 32}
 33
 34void
 35xfs_defer_drain_wait_enable(void)
 36{
 37	static_branch_inc(&xfs_defer_drain_waiter_gate);
 38}
 39
 40void
 41xfs_defer_drain_init(
 42	struct xfs_defer_drain	*dr)
 43{
 44	atomic_set(&dr->dr_count, 0);
 45	init_waitqueue_head(&dr->dr_waiters);
 46}
 47
 48void
 49xfs_defer_drain_free(struct xfs_defer_drain	*dr)
 50{
 51	ASSERT(atomic_read(&dr->dr_count) == 0);
 52}
 53
 54/* Increase the pending intent count. */
 55static inline void xfs_defer_drain_grab(struct xfs_defer_drain *dr)
 56{
 57	atomic_inc(&dr->dr_count);
 58}
 59
 60static inline bool has_waiters(struct wait_queue_head *wq_head)
 61{
 62	/*
 63	 * This memory barrier is paired with the one in set_current_state on
 64	 * the waiting side.
 65	 */
 66	smp_mb__after_atomic();
 67	return waitqueue_active(wq_head);
 68}
 69
 70/* Decrease the pending intent count, and wake any waiters, if appropriate. */
 71static inline void xfs_defer_drain_rele(struct xfs_defer_drain *dr)
 72{
 73	if (atomic_dec_and_test(&dr->dr_count) &&
 74	    static_branch_unlikely(&xfs_defer_drain_waiter_gate) &&
 75	    has_waiters(&dr->dr_waiters))
 76		wake_up(&dr->dr_waiters);
 77}
 78
 79/* Are there intents pending? */
 80static inline bool xfs_defer_drain_busy(struct xfs_defer_drain *dr)
 81{
 82	return atomic_read(&dr->dr_count) > 0;
 83}
 84
 85/*
 86 * Wait for the pending intent count for a drain to hit zero.
 87 *
 88 * Callers must not hold any locks that would prevent intents from being
 89 * finished.
 90 */
 91static inline int xfs_defer_drain_wait(struct xfs_defer_drain *dr)
 92{
 93	return wait_event_killable(dr->dr_waiters, !xfs_defer_drain_busy(dr));
 94}
 95
 96/*
 97 * Get a passive reference to the group that contains a fsbno and declare an
 98 * intent to update its metadata.
 99 *
100 * Other threads that need exclusive access can decide to back off if they see
101 * declared intentions.
102 */
103struct xfs_group *
104xfs_group_intent_get(
105	struct xfs_mount	*mp,
106	xfs_fsblock_t		fsbno,
107	enum xfs_group_type	type)
108{
109	struct xfs_group	*xg;
110
111	xg = xfs_group_get_by_fsb(mp, fsbno, type);
112	if (!xg)
113		return NULL;
114	trace_xfs_group_intent_hold(xg, __return_address);
115	xfs_defer_drain_grab(&xg->xg_intents_drain);
116	return xg;
117}
118
119/*
120 * Release our intent to update this groups metadata, and then release our
121 * passive ref to it.
122 */
123void
124xfs_group_intent_put(
125	struct xfs_group	*xg)
126{
127	trace_xfs_group_intent_rele(xg, __return_address);
128	xfs_defer_drain_rele(&xg->xg_intents_drain);
129	xfs_group_put(xg);
130}
131
132/*
133 * Wait for the intent update count for this AG to hit zero.
134 * Callers must not hold any AG header buffers.
135 */
136int
137xfs_group_intent_drain(
138	struct xfs_group	*xg)
139{
140	trace_xfs_group_wait_intents(xg, __return_address);
141	return xfs_defer_drain_wait(&xg->xg_intents_drain);
142}
143
144/*
145 * Has anyone declared an intent to update this group?
146 */
147bool
148xfs_group_intent_busy(
149	struct xfs_group	*xg)
150{
151	return xfs_defer_drain_busy(&xg->xg_intents_drain);
152}