linux-kernel - [PATCH] ext4: fast_commit: assert i_data

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Message-ID: <20251222032655.87056-1-me@linux.beauty>
Date: Mon, 22 Dec 2025 11:26:54 +0800
From: Li Chen <me@...ux.beauty>
To: "Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Li Chen <me@...ux.beauty>
Subject: [PATCH] ext4: fast_commit: assert i_data_sem only before sleep

ext4_fc_track_inode() may enter the wait loop with
EXT4_STATE_FC_COMMITTING set but then observe it cleared before it
actually sleeps. Asserting i_data_sem not held unconditionally triggers
false lockdep warnings from paths that hold i_data_sem (e.g. fallocate)
but never reach schedule().

Move lockdep_assert_not_held(&ei->i_data_sem) onto the schedule() path
so it only fires when we are really going to sleep.

Signed-off-by: Li Chen <me@...ux.beauty>
---
 fs/ext4/fast_commit.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index f3914f46bcf6..f24b4fea7421 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -577,8 +577,6 @@ void ext4_fc_track_inode(handle_t *handle, struct inode *inode)
 	 * 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,
@@ -592,8 +590,10 @@ 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)) {
+			lockdep_assert_not_held(&ei->i_data_sem);
 			schedule();
+		}
 		finish_wait(wq, &wait.wq_entry);
 	}
 
-- 
2.51.0