linux-kernel - [PATCH] f2fs: avoid the deadlock case when stopping discard thread

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Date: Tue, 19 Mar 2024 17:14:42 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Cc: Jaegeuk Kim <jaegeuk@...nel.org>
Subject: [PATCH] f2fs: avoid the deadlock case when stopping discard thread

f2fs_ioc_shutdown(F2FS_GOING_DOWN_NOSYNC)  issue_discard_thread
 - mnt_want_write_file()
   - sb_start_write(SB_FREEZE_WRITE)
                                             - sb_start_intwrite(SB_FREEZE_FS);
 - f2fs_stop_checkpoint(sbi, false,            : waiting
    STOP_CP_REASON_SHUTDOWN);
 - f2fs_stop_discard_thread(sbi);
   - kthread_stop()
     : waiting

 - mnt_drop_write_file(filp);

Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---
 fs/f2fs/segment.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 4fd76e867e0a..088b8c48cffa 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1923,7 +1923,9 @@ static int issue_discard_thread(void *data)
 			continue;
 		}
 
-		sb_start_intwrite(sbi->sb);
+		/* Avoid the deadlock from F2FS_GOING_DOWN_NOSYNC. */
+		if (!sb_start_intwrite_trylock(sbi->sb))
+			continue;
 
 		issued = __issue_discard_cmd(sbi, &dpolicy);
 		if (issued > 0) {
-- 
2.44.0.291.gc1ea87d7ee-goog