This is a note to let you know that I've just added the patch titled
f2fs: quota: fix potential deadlock
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
f2fs-quota-fix-potential-deadlock.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 8ae24aacc1020dac21b216841199f68f8cf1e5ec
Author: Chao Yu <chao@xxxxxxxxxx>
Date: Fri Sep 3 10:38:11 2021 +0800
f2fs: quota: fix potential deadlock
[ Upstream commit a5c0042200b28fff3bde6fa128ddeaef97990f8d ]
As Yi Zhuang reported in bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=214299
There is potential deadlock during quota data flush as below:
Thread A: Thread B:
f2fs_dquot_acquire
down_read(&sbi->quota_sem)
f2fs_write_checkpoint
block_operations
f2fs_look_all
down_write(&sbi->cp_rwsem)
f2fs_quota_write
f2fs_write_begin
__do_map_lock
f2fs_lock_op
down_read(&sbi->cp_rwsem)
__need_flush_qutoa
down_write(&sbi->quota_sem)
This patch changes block_operations() to use trylock, if it fails,
it means there is potential quota data updater, in this condition,
let's flush quota data first and then trylock again to check dirty
status of quota data.
The side effect is: in heavy race condition (e.g. multi quota data
upaters vs quota data flusher), it may decrease the probability of
synchronizing quota data successfully in checkpoint() due to limited
retry time of quota flush.
Reported-by: Yi Zhuang <zhuangyi1@xxxxxxxxxx>
Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 83e9bc0f91ffd..7b02827242312 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1162,7 +1162,8 @@ static bool __need_flush_quota(struct f2fs_sb_info *sbi)
if (!is_journalled_quota(sbi))
return false;
- down_write(&sbi->quota_sem);
+ if (!down_write_trylock(&sbi->quota_sem))
+ return true;
if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH)) {
ret = false;
} else if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR)) {
