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_drain_rele.  If the
17 * compiler supports jump labels, the static branch will be replaced by a nop
18 * sled when there are no xfs_drain_wait callers.  Online fsck is currently
19 * 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_drain_waiter_gate);
27
28void
29xfs_drain_wait_disable(void)
30{
31	static_branch_dec(&xfs_drain_waiter_gate);
32}
33
34void
35xfs_drain_wait_enable(void)
36{
37	static_branch_inc(&xfs_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_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 an AG and declare an intent to update its
98 * metadata.
99 */
100struct xfs_perag *
101xfs_perag_intent_get(
102	struct xfs_mount	*mp,
103	xfs_agnumber_t		agno)
104{
105	struct xfs_perag	*pag;
106
107	pag = xfs_perag_get(mp, agno);
108	if (!pag)
109		return NULL;
110
111	xfs_perag_intent_hold(pag);
112	return pag;
113}
114
115/*
116 * Release our intent to update this AG's metadata, and then release our
117 * passive ref to the AG.
118 */
119void
120xfs_perag_intent_put(
121	struct xfs_perag	*pag)
122{
123	xfs_perag_intent_rele(pag);
124	xfs_perag_put(pag);
125}
126
127/*
128 * Declare an intent to update AG metadata.  Other threads that need exclusive
129 * access can decide to back off if they see declared intentions.
130 */
131void
132xfs_perag_intent_hold(
133	struct xfs_perag	*pag)
134{
135	trace_xfs_perag_intent_hold(pag, __return_address);
136	xfs_defer_drain_grab(&pag->pag_intents_drain);
137}
138
139/* Release our intent to update this AG's metadata. */
140void
141xfs_perag_intent_rele(
142	struct xfs_perag	*pag)
143{
144	trace_xfs_perag_intent_rele(pag, __return_address);
145	xfs_defer_drain_rele(&pag->pag_intents_drain);
146}
147
148/*
149 * Wait for the intent update count for this AG to hit zero.
150 * Callers must not hold any AG header buffers.
151 */
152int
153xfs_perag_intent_drain(
154	struct xfs_perag	*pag)
155{
156	trace_xfs_perag_wait_intents(pag, __return_address);
157	return xfs_defer_drain_wait(&pag->pag_intents_drain);
158}
159
160/* Has anyone declared an intent to update this AG? */
161bool
162xfs_perag_intent_busy(
163	struct xfs_perag	*pag)
164{
165	return xfs_defer_drain_busy(&pag->pag_intents_drain);
166}
167