Re: [f2fs-dev] [PATCH] f2fs: quota: fix potential deadlock

[Chao Yu <chao@kernel.org>]

On 2022/1/4 23:17, Greg KH wrote:
> 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@vger.kernel.org # v5.3+
>>>> Reported-by: Yi Zhuang <zhuangyi1@huawei.com>
>>>> Signed-off-by: Chao Yu <chao@kernel.org>
>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>>> ---
>>>>    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?  :)

Oops, no, so 5.4 and 5.10 is enough. ;)
We can skip 5.15 since this patch was merged in 5.15-rc1 at the first time.

> 
>> 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...

Copied.

Thank you for the help!

Thanks,

> 
> thanks,
> 
> greg k-h


_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel