linux-kernel - Re: [PATCH v2] vfs: __read_cache_page should use gfp argument rather than GFP

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Message-ID: <4EF24758.5030704@oracle.com>
Date:	Wed, 21 Dec 2011 14:53:44 -0600
From:	Dave Kleikamp <dave.kleikamp@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	jfs-discussion@...ts.sourceforge.net,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Florian Mickler <florian@...kler.org>, davem@...emloft.net,
	Al Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org
Subject: Re: [PATCH v2] vfs: __read_cache_page should use gfp argument rather
 than GFP_KERNEL

On 12/21/2011 02:28 PM, Andrew Morton wrote:
> On Wed, 21 Dec 2011 11:05:48 -0600
> Dave Kleikamp <dave.kleikamp@...cle.com> wrote:
> 
>> [ updated to remove now-obsolete comment in read_cache_page_gfp()]
>>
>> lockdep reports a deadlock in jfs because a special inode's rw semaphore
>> is taken recursively. The mapping's gfp mask is GFP_NOFS, but is not used
>> when __read_cache_page() calls add_to_page_cache_lru().
> 
> Well hang on, it's not just a lockdep splat.  The kernel actually will
> deadlock if we reenter JFS via this GFP_KERNEL allocation attempt, yes?

Yes, it could result in a real deadlock.

> Was that GFP_NOFS allocation recently added to JFS?  If not then we
> should backport this deadlock fix into -stable, no?

Yes, that would make sense.

Shaggy
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