From: Chao Yu chao@kernel.org
commit a5c0042200b28fff3bde6fa128ddeaef97990f8d upstream.
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@huawei.com Signed-off-by: Chao Yu chao@kernel.org Signed-off-by: Jaegeuk Kim jaegeuk@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/f2fs/checkpoint.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/f2fs/checkpoint.c +++ b/fs/f2fs/checkpoint.c @@ -1144,7 +1144,8 @@ static bool __need_flush_quota(struct f2 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)) {