[RFC PATCH v2 1/2] ext4: fast_commit: assert i_data_sem only before sleep

Li Chen
2025-12-22T15:19:27Z

ext4_fc_track_inode() can return without sleeping when
EXT4_STATE_FC_COMMITTING is already clear. The lockdep assertion for
ei->i_data_sem was done unconditionally before the wait loop, which can
WARN in call paths that hold i_data_sem even though we never block. Move
lockdep_assert_not_held(&ei->i_data_sem) into the actual sleep path,
right before schedule().

Signed-off-by: Li Chen <me@linux.beauty>
---
fs/ext4/fast_commit.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index fa66b08de999..3bcdd4619de1 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -566,13 +566,6 @@ void ext4_fc_track_inode(handle_t *handle, struct inode *inode)
if (ext4_test_mount_flag(inode->i_sb, EXT4_MF_FC_INELIGIBLE))
return;

- /*
- * If we come here, we may sleep while waiting for the inode to
- * commit. We shouldn't be holding i_data_sem when we go to sleep since
- * the commit path needs to grab the lock while committing the inode.
- */
- lockdep_assert_not_held(&ei->i_data_sem);
-
while (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING)) {
#if (BITS_PER_LONG < 64)
DEFINE_WAIT_BIT(wait, &ei->i_state_flags,
@@ -586,8 +579,16 @@ void ext4_fc_track_inode(handle_t *handle, struct inode *inode)
EXT4_STATE_FC_COMMITTING);
#endif
prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
- if (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING))
+ if (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING)) {
+ /*
+ * We might sleep while waiting for the inode to commit.
+ * We shouldn't be holding i_data_sem when we go to sleep
+ * since the commit path may grab it while committing this
+ * inode.
+ */
+ lockdep_assert_not_held(&ei->i_data_sem);
schedule();
+ }
finish_wait(wq, &wait.wq_entry);
}

--
2.51.0