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

[Li Chen <me@linux.beauty>]

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