[PATCH 6.18 255/641] ext4: fast commit: make s_fc_lock reclaim-safe

Greg Kroah-Hartman
2026-02-25T01:46:43Z

6.18-stable review patch. If anyone has any objections, please let me know.

------------------

From: Li Chen <me@linux.beauty>

[ Upstream commit 491f2927ae097e2d405afe0b3fe841931ab8aad2 ]

s_fc_lock can be acquired from inode eviction and thus is
reclaim unsafe. Since the fast commit path holds s_fc_lock while writing
the commit log, allocations under the lock can enter reclaim and invert
the lock order with fs_reclaim. Add ext4_fc_lock()/ext4_fc_unlock()
helpers which acquire s_fc_lock under memalloc_nofs_save()/restore()
context and use them everywhere so allocations under the lock cannot
recurse into filesystem reclaim.

Fixes: 6593714d67ba ("ext4: hold s_fc_lock while during fast commit")
Signed-off-by: Li Chen <me@linux.beauty>
Reviewed-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260106120621.440126-1-me@linux.beauty
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ext4/ext4.h | 16 ++++++++++++++
fs/ext4/fast_commit.c | 51 ++++++++++++++++++++++++-------------------
2 files changed, 44 insertions(+), 23 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 57087da6c7bee..933297251f66a 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1771,6 +1771,10 @@ struct ext4_sb_info {
* Main fast commit lock. This lock protects accesses to the
* following fields:
* ei->i_fc_list, s_fc_dentry_q, s_fc_q, s_fc_bytes, s_fc_bh.
+ *
+ * s_fc_lock can be taken from reclaim context (inode eviction) and is
+ * thus reclaim unsafe. Use ext4_fc_lock()/ext4_fc_unlock() helpers
+ * when acquiring / releasing the lock.
*/
struct mutex s_fc_lock;
struct buffer_head *s_fc_bh;
@@ -1815,6 +1819,18 @@ static inline void ext4_writepages_up_write(struct super_block *sb, int ctx)
percpu_up_write(&EXT4_SB(sb)->s_writepages_rwsem);
}

+static inline int ext4_fc_lock(struct super_block *sb)
+{
+ mutex_lock(&EXT4_SB(sb)->s_fc_lock);
+ return memalloc_nofs_save();
+}
+
+static inline void ext4_fc_unlock(struct super_block *sb, int ctx)
+{
+ memalloc_nofs_restore(ctx);
+ mutex_unlock(&EXT4_SB(sb)->s_fc_lock);
+}
+
static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
{
return ino == EXT4_ROOT_INO ||
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index fa66b08de9994..5bd57d7f921b9 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -231,16 +231,16 @@ static bool ext4_fc_disabled(struct super_block *sb)
void ext4_fc_del(struct inode *inode)
{
struct ext4_inode_info *ei = EXT4_I(inode);
- struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
struct ext4_fc_dentry_update *fc_dentry;
wait_queue_head_t *wq;
+ int alloc_ctx;

if (ext4_fc_disabled(inode->i_sb))
return;

- mutex_lock(&sbi->s_fc_lock);
+ alloc_ctx = ext4_fc_lock(inode->i_sb);
if (list_empty(&ei->i_fc_list) && list_empty(&ei->i_fc_dilist)) {
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(inode->i_sb, alloc_ctx);
return;
}

@@ -275,9 +275,9 @@ void ext4_fc_del(struct inode *inode)
#endif
prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
if (ext4_test_inode_state(inode, EXT4_STATE_FC_FLUSHING_DATA)) {
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(inode->i_sb, alloc_ctx);
schedule();
- mutex_lock(&sbi->s_fc_lock);
+ alloc_ctx = ext4_fc_lock(inode->i_sb);
}
finish_wait(wq, &wait.wq_entry);
}
@@ -288,7 +288,7 @@ void ext4_fc_del(struct inode *inode)
* dentry create references, since it is not needed to log it anyways.
*/
if (list_empty(&ei->i_fc_dilist)) {
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(inode->i_sb, alloc_ctx);
return;
}

@@ -298,7 +298,7 @@ void ext4_fc_del(struct inode *inode)
list_del_init(&fc_dentry->fcd_dilist);

WARN_ON(!list_empty(&ei->i_fc_dilist));
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(inode->i_sb, alloc_ctx);

release_dentry_name_snapshot(&fc_dentry->fcd_name);
kmem_cache_free(ext4_fc_dentry_cachep, fc_dentry);
@@ -315,6 +315,7 @@ void ext4_fc_mark_ineligible(struct super_block *sb, int reason, handle_t *handl
tid_t tid;
bool has_transaction = true;
bool is_ineligible;
+ int alloc_ctx;

if (ext4_fc_disabled(sb))
return;
@@ -329,12 +330,12 @@ void ext4_fc_mark_ineligible(struct super_block *sb, int reason, handle_t *handl
has_transaction = false;
read_unlock(&sbi->s_journal->j_state_lock);
}
- mutex_lock(&sbi->s_fc_lock);
+ alloc_ctx = ext4_fc_lock(sb);
is_ineligible = ext4_test_mount_flag(sb, EXT4_MF_FC_INELIGIBLE);
if (has_transaction && (!is_ineligible || tid_gt(tid, sbi->s_fc_ineligible_tid)))
sbi->s_fc_ineligible_tid = tid;
ext4_set_mount_flag(sb, EXT4_MF_FC_INELIGIBLE);
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(sb, alloc_ctx);
WARN_ON(reason >= EXT4_FC_REASON_MAX);
sbi->s_fc_stats.fc_ineligible_reason_count[reason]++;
}
@@ -358,6 +359,7 @@ static int ext4_fc_track_template(
struct ext4_inode_info *ei = EXT4_I(inode);
struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
tid_t tid = 0;
+ int alloc_ctx;
int ret;

tid = handle->h_transaction->t_tid;
@@ -373,14 +375,14 @@ static int ext4_fc_track_template(
if (!enqueue)
return ret;

- mutex_lock(&sbi->s_fc_lock);
+ alloc_ctx = ext4_fc_lock(inode->i_sb);
if (list_empty(&EXT4_I(inode)->i_fc_list))
list_add_tail(&EXT4_I(inode)->i_fc_list,
(sbi->s_journal->j_flags & JBD2_FULL_COMMIT_ONGOING ||
sbi->s_journal->j_flags & JBD2_FAST_COMMIT_ONGOING) ?
&sbi->s_fc_q[FC_Q_STAGING] :
&sbi->s_fc_q[FC_Q_MAIN]);
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(inode->i_sb, alloc_ctx);

return ret;
}
@@ -402,6 +404,7 @@ static int __track_dentry_update(handle_t *handle, struct inode *inode,
struct inode *dir = dentry->d_parent->d_inode;
struct super_block *sb = inode->i_sb;
struct ext4_sb_info *sbi = EXT4_SB(sb);
+ int alloc_ctx;

spin_unlock(&ei->i_fc_lock);

@@ -425,7 +428,7 @@ static int __track_dentry_update(handle_t *handle, struct inode *inode,
take_dentry_name_snapshot(&node->fcd_name, dentry);
INIT_LIST_HEAD(&node->fcd_dilist);
INIT_LIST_HEAD(&node->fcd_list);
- mutex_lock(&sbi->s_fc_lock);
+ alloc_ctx = ext4_fc_lock(sb);
if (sbi->s_journal->j_flags & JBD2_FULL_COMMIT_ONGOING ||
sbi->s_journal->j_flags & JBD2_FAST_COMMIT_ONGOING)
list_add_tail(&node->fcd_list,
@@ -446,7 +449,7 @@ static int __track_dentry_update(handle_t *handle, struct inode *inode,
WARN_ON(!list_empty(&ei->i_fc_dilist));
list_add_tail(&node->fcd_dilist, &ei->i_fc_dilist);
}
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(sb, alloc_ctx);
spin_lock(&ei->i_fc_lock);

return 0;
@@ -1046,18 +1049,19 @@ static int ext4_fc_perform_commit(journal_t *journal)
struct blk_plug plug;
int ret = 0;
u32 crc = 0;
+ int alloc_ctx;

/*
* Step 1: Mark all inodes on s_fc_q[MAIN] with
* EXT4_STATE_FC_FLUSHING_DATA. This prevents these inodes from being
* freed until the data flush is over.
*/
- mutex_lock(&sbi->s_fc_lock);
+ alloc_ctx = ext4_fc_lock(sb);
list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
ext4_set_inode_state(&iter->vfs_inode,
EXT4_STATE_FC_FLUSHING_DATA);
}
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(sb, alloc_ctx);

/* Step 2: Flush data for all the eligible inodes. */
ret = ext4_fc_flush_data(journal);
@@ -1067,7 +1071,7 @@ static int ext4_fc_perform_commit(journal_t *journal)
* any error from step 2. This ensures that waiters waiting on
* EXT4_STATE_FC_FLUSHING_DATA can resume.
*/
- mutex_lock(&sbi->s_fc_lock);
+ alloc_ctx = ext4_fc_lock(sb);
list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
ext4_clear_inode_state(&iter->vfs_inode,
EXT4_STATE_FC_FLUSHING_DATA);
@@ -1084,7 +1088,7 @@ static int ext4_fc_perform_commit(journal_t *journal)
* prepare_to_wait() in ext4_fc_del().
*/
smp_mb();
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(sb, alloc_ctx);

/*
* If we encountered error in Step 2, return it now after clearing
@@ -1101,12 +1105,12 @@ static int ext4_fc_perform_commit(journal_t *journal)
* previous handles are now drained. We now mark the inodes on the
* commit queue as being committed.
*/
- mutex_lock(&sbi->s_fc_lock);
+ alloc_ctx = ext4_fc_lock(sb);
list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
ext4_set_inode_state(&iter->vfs_inode,
EXT4_STATE_FC_COMMITTING);
}
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(sb, alloc_ctx);
jbd2_journal_unlock_updates(journal);

/*
@@ -1117,6 +1121,7 @@ static int ext4_fc_perform_commit(journal_t *journal)
blkdev_issue_flush(journal->j_fs_dev);

blk_start_plug(&plug);
+ alloc_ctx = ext4_fc_lock(sb);
/* Step 6: Write fast commit blocks to disk. */
if (sbi->s_fc_bytes == 0) {
/*
@@ -1134,7 +1139,6 @@ static int ext4_fc_perform_commit(journal_t *journal)
}

/* Step 6.2: Now write all the dentry updates. */
- mutex_lock(&sbi->s_fc_lock);
ret = ext4_fc_commit_dentry_updates(journal, &crc);
if (ret)
goto out;
@@ -1156,7 +1160,7 @@ static int ext4_fc_perform_commit(journal_t *journal)
ret = ext4_fc_write_tail(sb, crc);

out:
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(sb, alloc_ctx);
blk_finish_plug(&plug);
return ret;
}
@@ -1290,6 +1294,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_inode_info *ei;
struct ext4_fc_dentry_update *fc_dentry;
+ int alloc_ctx;

if (full && sbi->s_fc_bh)
sbi->s_fc_bh = NULL;
@@ -1297,7 +1302,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
trace_ext4_fc_cleanup(journal, full, tid);
jbd2_fc_release_bufs(journal);

- mutex_lock(&sbi->s_fc_lock);
+ alloc_ctx = ext4_fc_lock(sb);
while (!list_empty(&sbi->s_fc_q[FC_Q_MAIN])) {
ei = list_first_entry(&sbi->s_fc_q[FC_Q_MAIN],
struct ext4_inode_info,
@@ -1356,7 +1361,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)

if (full)
sbi->s_fc_bytes = 0;
- mutex_unlock(&sbi->s_fc_lock);
+ ext4_fc_unlock(sb, alloc_ctx);
trace_ext4_fc_stats(sb);
}

--
2.51.0