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

박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@lge.com)
2017-09-26T07:17:01Z

> -----Original Message-----
> From: Coly Li [mailto:i@coly.li]
> Sent: Tuesday, September 26, 2017 4:09 PM
> To: Michael Lyle; 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
>
> On 2017/9/26 下午12:38, Michael Lyle wrote:
> > 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.
> >
>
> Hi Mike,
>
> Good catch! I see llist_del_all() but forget cl->list can be modified in
> closure_wait(). Yes there is potential chance to mislead
> llist_for_each_entry() to iterate wrong list.
> llist_for_each_entry_safe() should be used here. I will send a fix to
> Jens, hope to catch up 4.14 still.

I see. You have a plan to do it. Please fix it.

Thank you.

> Thanks!
> --
> Coly Li