Re: [PATCH 04/12] bcache: Don't reinvent the wheel but use existing llist API

Coly Li
2017-09-26T07:23:11Z

On 2017/9/26 下午3:15, 박병철/선임연구원/SW
Platform(연)AOT팀(byungchul.park@lge.com) wrote:
>> -----Original Message-----
>> From: Coly Li [mailto:i@coly.li]
>> Sent: Tuesday, September 26, 2017 4:09 PM
>> To: 박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@lge.com);
>> Michael Lyle; Coly Li
>> Cc: linux-bcache@vger.kernel.org; linux-block@vger.kernel.org;
>> axboe@kernel.dk; Eric Wheeler; Kent Overstreet; kernel-team@lge.com
>> Subject: Re: [PATCH 04/12] bcache: Don't reinvent the wheel but use existing
>> llist API
>>
>> On 2017/9/26 下午2:39, 박병철/선임연구원/SW
>> Platform(연)AOT팀(byungchul.park@lge.com) wrote:
>>>> -----Original Message-----
>>>> From: Michael Lyle [mailto:mlyle@lyle.org]
>>>> Sent: Tuesday, September 26, 2017 1:38 PM
>>>> To: Coly Li
>>>> Cc: linux-bcache@vger.kernel.org; linux-block@vger.kernel.org;
>>>> axboe@kernel.dk; Eric Wheeler; Byungchul Park; Kent Overstreet
>>>> Subject: Re: [PATCH 04/12] bcache: Don't reinvent the wheel but use existing
>>>> llist API
>>>>
>>>> I believe this introduces a critical bug.
>>>>
>>>> cl->list is used to link together the llists for both things waiting,
>>>> and for things that are being woken.
>>>>
>>>> If a closure that is woken decides to wait again, it will corrupt the
>>>> llist that __closure_wake_up is using.
>>>>
>>>> The previous iteration structure gets the next element of the list
>>>> before waking and is therefore safe.
>>>
>>> Do you mean we have to use llist_for_each_entry_safe() instead of non-safe
>> version?
>>> Is it ok if we use it instead?
>>
>> Yes, we should use llist_for_each_entry_safe(), there is a quite
>> implicit race here.
>
> Hi coly,
>
> As you know, my first patch used the safe version, but you suggested to replace
> It with non-safe one. :(

No doubt, it's my fault. I didn't find the implicit potential race.

> I will change it so it does the same as the original patch did. :)

Yes, please. Because the original patch is merged into Linux upstream,
post a fix to replace llist_for_each_entry() by
llist_for_each_entry_safe(). We still have chance to catch up 4.14.

Thank you !

--
Coly Li