linux-kernel - Re: [PATCH] aio: ensure access to ctx->ring

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Message-ID: <20140325185727.GU4173@kvack.org>
Date:	Tue, 25 Mar 2014 14:57:27 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Gu Zheng <guz.fnst@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Dave Jones <davej@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>, jmoyer@...hat.com,
	kosaki.motohiro@...fujitsu.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	miaox@...fujitsu.com, linux-aio@...ck.org,
	fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] aio: ensure access to ctx->ring_pages is correctly serialised

Hi Sasha,

On Tue, Mar 25, 2014 at 01:47:40PM -0400, Sasha Levin wrote:
> On 03/24/2014 03:07 PM, Benjamin LaHaise wrote:
...
> >Yeah, that's a problem -- thanks for the report.  The ring_lock mutex can't
> >be nested inside of mmap_sem, as aio_read_events_ring() can take a page
> >fault while holding ring_mutex.  That makes the following change required.
> >I'll fold this change into the patch that caused this issue.
> 
> Yup, that does the trick.
> 
> Could you please add something to document why this is a trylock instead of 
> a lock? If
> I were reading the code there's no way I'd understand what's the reason 
> behind it
> without knowing of this bug report.

Done.  I've updated the patch in my aio-next.git tree, so it should be in 
tomorrow's linux-next, and will give it one last day for any further problem 
reports.  Thanks for testing!

		-ben

> Thanks,
> Sasha

-- 
"Thought is the essence of where you are now."
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