On Tue, Jan 04, 2022 at 11:05:36PM +0800, Chao Yu wrote: > On 2022/1/4 21:18, Greg KH wrote: > > On Tue, Jan 04, 2022 at 09:05:13PM +0800, Chao Yu wrote: > > > 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. > > > > > > Fixes: db6ec53b7e03 ("f2fs: add a rw_sem to cover quota flag changes") > > > Cc: stable@xxxxxxxxxxxxxxx # v5.3+ > > > Reported-by: Yi Zhuang <zhuangyi1@xxxxxxxxxx> > > > Signed-off-by: Chao Yu <chao@xxxxxxxxxx> > > > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> > > > --- > > > fs/f2fs/checkpoint.c | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c > > > index 83e9bc0f91ff..7b0282724231 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)) { > > > -- > > > 2.32.0 > > > > > > > What stable tree(s) is this for? > > Oh, please help to try applying to 5.4, 5.10, and 5.15 stable trees, thanks! This is already in the 5.15.6 kernel release, do you need it applied there again? :) > Let me know if I should send patches for different trees separately. If the same commit here works for all of the above, it's fine. But for some reason I don't think it will work in 5.15.y... thanks, greg k-h
