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bcachefs: seqmutex; fix a lockdep splat

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We can't be holding btree_trans_lock while copying to user space, which
might incur a page fault. To fix this, convert it to a seqmutex so we
can unlock/relock.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2023-06-19 21:01:13 -04:00
parent 6547ebabda
commit a5b696ee6e
5 changed files with 96 additions and 23 deletions
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3
fs/bcachefs/bcachefs.h
View File

@ -208,6 +208,7 @@
#include "fifo.h"
#include "nocow_locking_types.h"
#include "opts.h"
#include "seqmutex.h"
#include "util.h"
#ifdef CONFIG_BCACHEFS_DEBUG
@ -779,7 +780,7 @@ struct bch_fs {
} btree_write_stats[BTREE_WRITE_TYPE_NR];
/* btree_iter.c: */
struct mutex btree_trans_lock;
struct seqmutex btree_trans_lock;
struct list_head btree_trans_list;
mempool_t btree_paths_pool;
mempool_t btree_trans_mem_pool;

18
fs/bcachefs/btree_iter.c
View File

@ -2991,7 +2991,7 @@ void __bch2_trans_init(struct btree_trans *trans, struct bch_fs *c, unsigned fn_
if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG_TRANSACTIONS)) {
struct btree_trans *pos;
mutex_lock(&c->btree_trans_lock);
seqmutex_lock(&c->btree_trans_lock);
list_for_each_entry(pos, &c->btree_trans_list, list) {
/*
* We'd much prefer to be stricter here and completely
@ -3009,7 +3009,7 @@ void __bch2_trans_init(struct btree_trans *trans, struct bch_fs *c, unsigned fn_
}
list_add_tail(&trans->list, &c->btree_trans_list);
list_add_done:
mutex_unlock(&c->btree_trans_lock);
seqmutex_unlock(&c->btree_trans_lock);
}
}
@ -3044,6 +3044,12 @@ void bch2_trans_exit(struct btree_trans *trans)
bch2_trans_unlock(trans);
if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG_TRANSACTIONS)) {
seqmutex_lock(&c->btree_trans_lock);
list_del(&trans->list);
seqmutex_unlock(&c->btree_trans_lock);
}
closure_sync(&trans->ref);
if (s)
@ -3055,12 +3061,6 @@ void bch2_trans_exit(struct btree_trans *trans)
check_btree_paths_leaked(trans);
if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG_TRANSACTIONS)) {
mutex_lock(&c->btree_trans_lock);
list_del(&trans->list);
mutex_unlock(&c->btree_trans_lock);
}
srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx);
bch2_journal_preres_put(&c->journal, &trans->journal_preres);
@ -3198,7 +3198,7 @@ int bch2_fs_btree_iter_init(struct bch_fs *c)
}
INIT_LIST_HEAD(&c->btree_trans_list);
mutex_init(&c->btree_trans_lock);
seqmutex_init(&c->btree_trans_lock);
ret = mempool_init_kmalloc_pool(&c->btree_paths_pool, 1,
sizeof(struct btree_path) * nr +

46
fs/bcachefs/debug.c
View File

@ -627,19 +627,26 @@ static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf,
struct bch_fs *c = i->c;
struct btree_trans *trans;
ssize_t ret = 0;
u32 seq;
i->ubuf = buf;
i->size = size;
i->ret = 0;
mutex_lock(&c->btree_trans_lock);
restart:
seqmutex_lock(&c->btree_trans_lock);
list_for_each_entry(trans, &c->btree_trans_list, list) {
if (trans->locking_wait.task->pid <= i->iter)
continue;
closure_get(&trans->ref);
seq = seqmutex_seq(&c->btree_trans_lock);
seqmutex_unlock(&c->btree_trans_lock);
ret = flush_buf(i);
if (ret)
break;
if (ret) {
closure_put(&trans->ref);
goto unlocked;
}
bch2_btree_trans_to_text(&i->buf, trans);
@ -651,9 +658,14 @@ static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf,
prt_newline(&i->buf);
i->iter = trans->locking_wait.task->pid;
}
mutex_unlock(&c->btree_trans_lock);
closure_put(&trans->ref);
if (!seqmutex_relock(&c->btree_trans_lock, seq))
goto restart;
}
seqmutex_unlock(&c->btree_trans_lock);
unlocked:
if (i->buf.allocation_failure)
ret = -ENOMEM;
@ -815,6 +827,7 @@ static ssize_t bch2_btree_deadlock_read(struct file *file, char __user *buf,
struct bch_fs *c = i->c;
struct btree_trans *trans;
ssize_t ret = 0;
u32 seq;
i->ubuf = buf;
i->size = size;
@ -822,21 +835,32 @@ static ssize_t bch2_btree_deadlock_read(struct file *file, char __user *buf,
if (i->iter)
goto out;
mutex_lock(&c->btree_trans_lock);
restart:
seqmutex_lock(&c->btree_trans_lock);
list_for_each_entry(trans, &c->btree_trans_list, list) {
if (trans->locking_wait.task->pid <= i->iter)
continue;
closure_get(&trans->ref);
seq = seqmutex_seq(&c->btree_trans_lock);
seqmutex_unlock(&c->btree_trans_lock);
ret = flush_buf(i);
if (ret)
break;
if (ret) {
closure_put(&trans->ref);
goto out;
}
bch2_check_for_deadlock(trans, &i->buf);
i->iter = trans->locking_wait.task->pid;
closure_put(&trans->ref);
if (!seqmutex_relock(&c->btree_trans_lock, seq))
goto restart;
}
mutex_unlock(&c->btree_trans_lock);
seqmutex_unlock(&c->btree_trans_lock);
out:
if (i->buf.allocation_failure)
ret = -ENOMEM;

48
fs/bcachefs/seqmutex.h Normal file
View File

@ -0,0 +1,48 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _BCACHEFS_SEQMUTEX_H
#define _BCACHEFS_SEQMUTEX_H
#include <linux/mutex.h>
struct seqmutex {
struct mutex lock;
u32 seq;
};
#define seqmutex_init(_lock) mutex_init(&(_lock)->lock)
static inline bool seqmutex_trylock(struct seqmutex *lock)
{
return mutex_trylock(&lock->lock);
}
static inline void seqmutex_lock(struct seqmutex *lock)
{
mutex_lock(&lock->lock);
}
static inline void seqmutex_unlock(struct seqmutex *lock)
{
lock->seq++;
mutex_unlock(&lock->lock);
}
static inline u32 seqmutex_seq(struct seqmutex *lock)
{
return lock->seq;
}
static inline bool seqmutex_relock(struct seqmutex *lock, u32 seq)
{
if (lock->seq != seq || !mutex_trylock(&lock->lock))
return false;
if (lock->seq != seq) {
mutex_unlock(&lock->lock);
return false;
}
return true;
}
#endif /* _BCACHEFS_SEQMUTEX_H */

4
fs/bcachefs/sysfs.c
View File

@ -379,7 +379,7 @@ static void bch2_btree_wakeup_all(struct bch_fs *c)
{
struct btree_trans *trans;
mutex_lock(&c->btree_trans_lock);
seqmutex_lock(&c->btree_trans_lock);
list_for_each_entry(trans, &c->btree_trans_list, list) {
struct btree_bkey_cached_common *b = READ_ONCE(trans->locking);
@ -387,7 +387,7 @@ static void bch2_btree_wakeup_all(struct bch_fs *c)
six_lock_wakeup_all(&b->lock);
}
mutex_unlock(&c->btree_trans_lock);
seqmutex_unlock(&c->btree_trans_lock);
}
SHOW(bch2_fs)