linux-kernel - Re: [PATCH] zram: fix possible race when checking idle

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Message-ID: <20150810003513.GB26074@js1304-P5Q-DELUXE>
Date:	Mon, 10 Aug 2015 09:35:13 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zram: fix possible race when checking idle_strm

On Fri, Aug 07, 2015 at 11:49:04PM +0900, Minchan Kim wrote:
> Hi Joonsoo,
> 
> On Fri, Aug 07, 2015 at 05:03:29PM +0900, Joonsoo Kim wrote:
> > Currently, when we enter the wait state due to lack of idle stream,
> > we check idle_strm list without holding the lock in expanding of
> > wait_event define. In this case, some one can see stale value and
> > process could fall into wait state without any upcoming wakeup process.
> > Although I didn't see any error related to this race, it should be fixed.
> 
> Long time ago, I wondered about lost wake-up problem and found a article.
> 
> http://www.linuxjournal.com/article/8144
> 
> >From then, I have thought such issue shouldn't happen if something is
> wrong since then and I believe it's same issue.
> 
> Could you point out exact code sequence about the problem you mentioned?

Hello,

I describe exact code sequence in reply of Sergey's mail.
It would fully describe the problem.

Thanks.
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