6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Chao Yu <chao@xxxxxxxxxx>
[ Upstream commit 930c6ab93492c4b15436524e704950b364b2930c ]
syzbot reports a f2fs bug as below:
------------[ cut here ]------------
WARNING: CPU: 1 PID: 58 at kernel/rcu/sync.c:177 rcu_sync_dtor+0xcd/0x180 kernel/rcu/sync.c:177
CPU: 1 UID: 0 PID: 58 Comm: kworker/1:2 Not tainted 6.10.0-syzkaller-12562-g1722389b0d86 #0
Workqueue: events destroy_super_work
RIP: 0010:rcu_sync_dtor+0xcd/0x180 kernel/rcu/sync.c:177
Call Trace:
percpu_free_rwsem+0x41/0x80 kernel/locking/percpu-rwsem.c:42
destroy_super_work+0xec/0x130 fs/super.c:282
process_one_work kernel/workqueue.c:3231 [inline]
process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
worker_thread+0x86d/0xd40 kernel/workqueue.c:3390
kthread+0x2f0/0x390 kernel/kthread.c:389
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
As Christian Brauner pointed out [1]: the root cause is f2fs sets
SB_RDONLY flag in internal function, rather than setting the flag
covered w/ sb->s_umount semaphore via remount procedure, then below
race condition causes this bug:
- freeze_super()
- sb_wait_write(sb, SB_FREEZE_WRITE)
- sb_wait_write(sb, SB_FREEZE_PAGEFAULT)
- sb_wait_write(sb, SB_FREEZE_FS)
- f2fs_handle_critical_error
- sb->s_flags |= SB_RDONLY
- thaw_super
- thaw_super_locked
- sb_rdonly() is true, so it skips
sb_freeze_unlock(sb, SB_FREEZE_FS)
- deactivate_locked_super
Since f2fs has almost the same logic as ext4 [2] when handling critical
error in filesystem if it mounts w/ errors=remount-ro option:
- set CP_ERROR_FLAG flag which indicates filesystem is stopped
- record errors to superblock
- set SB_RDONLY falg
Once we set CP_ERROR_FLAG flag, all writable interfaces can detect the
flag and stop any further updates on filesystem. So, it is safe to not
set SB_RDONLY flag, let's remove the logic and keep in line w/ ext4 [3].
[1] https://lore.kernel.org/all/20240729-himbeeren-funknetz-96e62f9c7aee@brauner
[2] https://lore.kernel.org/all/20240729132721.hxih6ehigadqf7wx@quack3
[3] https://lore.kernel.org/linux-ext4/20240805201241.27286-1-jack@xxxxxxx
Fixes: b62e71be2110 ("f2fs: support errors=remount-ro|continue|panic mountoption")
Reported-by: syzbot+20d7e439f76bbbd863a7@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/all/000000000000b90a8e061e21d12f@xxxxxxxxxx/
Cc: Jan Kara <jack@xxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/f2fs/super.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 2bec5176df65d..37fa7e32835a3 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4137,12 +4137,14 @@ void f2fs_handle_critical_error(struct f2fs_sb_info *sbi, unsigned char reason,
}
f2fs_warn(sbi, "Remounting filesystem read-only");
+
/*
- * Make sure updated value of ->s_mount_flags will be visible before
- * ->s_flags update
+ * We have already set CP_ERROR_FLAG flag to stop all updates
+ * to filesystem, so it doesn't need to set SB_RDONLY flag here
+ * because the flag should be set covered w/ sb->s_umount semaphore
+ * via remount procedure, otherwise, it will confuse code like
+ * freeze_super() which will lead to deadlocks and other problems.
*/
- smp_wmb();
- sb->s_flags |= SB_RDONLY;
}
static void f2fs_record_error_work(struct work_struct *work)
--
2.43.0
