linux-kernel - Re: JFFS2 deadlock

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Date:	Thu, 25 Feb 2016 07:46:20 +0000
From:	Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
To:	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"Thomas.Betker@...de-schwarz.com" <Thomas.Betker@...de-schwarz.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"sztomi89@...il.com" <sztomi89@...il.com>,
	"wangzaiwei@...-vision.cn" <wangzaiwei@...-vision.cn>,
	"deng.chao1@....com.cn" <deng.chao1@....com.cn>,
	"liu.ming50@...il.com" <liu.ming50@...il.com>,
	"dedekind1@...il.com" <dedekind1@...il.com>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"linux-mtd-bounces@...ts.infradead.org" 
	<linux-mtd-bounces@...ts.infradead.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"computersforpeace@...il.com" <computersforpeace@...il.com>
Subject: Re: JFFS2 deadlock

On Thu, 2016-02-18 at 10:57 +0100, Thomas.Betker@...de-schwarz.com wrote:
> Hello David:
> 
> > 
> > > 
> > > Please could you try what's in the tree at
> > > http://git.infradead.org/users/dwmw2/jffs2-fixes.git
> > 
> > Your patch looks much simpler, and I will definitely test it. It may
> > take a few days, though, as I have to unearth the test scripts, and 
> > find a time slot for testing.
> Here is what I did (sorry for the wait, things were piling up):
> 
> 1) Removed Deng Chao's patch from my kernel, added your patch "jffs2: Fix 
> page lock / f->sem deadlock". I am still on linux-3.14, but jffs2 hasn't 
> changed much since then, so this shouldn't make a difference. Added a 
> printk() before mutex_unlock(&f->sem) to check if the prospective page was 
> locked, i.e. if the deadlock situation actually occurs.
> 
> 2) On my target system, started wangzaiwei's test (with some fixes), plus 
> a loop copying a large file over and over (to get GC rolling, which 
> increases the chance of a deadlock).
> 
> 3) After 24 hours, the system was still alive, and the printk() had been 
> hit 32 times.
> 
> So yes, I am confident that your patch avoids the deadlock, and if that's 
> good enough for you, please add my Tested-by:. However, I am going to run 
> some more stress tests here just to check that there weren't any 
> unexpected side effects. (Don't get me wrong -- I am sure the patch is 
> fine, but for me it's a case of "once bitten, twice shy" ...)

Can we get this upstream before next release? I don't think there will much more
testing at this point.

 Jocke