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? thanks, greg k-h
