This is a temporary patch which should not go to linux.git. syzbot is hitting hung task problems at __sb_start_write() [1]. atomic_long_read(&sem->rw_sem.count) says that percpu_down_read() was blocked because somebody has called percpu_down_write(). But since we believe that syzbot is not doing ioctl(FIFREEZE) requests, let's check who is calling percpu_down_write() from freeze_super(). Since it is impossible to reproduce this problem locally, this patch was made in order to test linux-next.git using syzbot infrastructure (and will be removed after the culprit is found). [1] https://syzkaller.appspot.com/bug?id=287aa8708bc940d0ca1645223c53dd4c2d203be6 Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> --- fs/super.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/super.c b/fs/super.c index 13647d4..4ec1b03 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1618,6 +1618,7 @@ int freeze_super(struct super_block *sb) return 0; } + WARN_ONCE(1, "Freezing superblock. Watch out for hung task.\n"); sb->s_writers.frozen = SB_FREEZE_WRITE; /* Release s_umount to preserve sb_start_write -> s_umount ordering */ up_write(&sb->s_umount); -- 1.8.3.1
