linux-kernel - Re: XFS memory allocation deadlock in 2.6.38

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Message-ID: <20110329193907.GK2310@cmpxchg.org>
Date:	Tue, 29 Mar 2011 21:39:07 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	'Christoph Hellwig' <hch@...radead.org>
Cc:	Sean Noonan <Sean.Noonan@...sigma.com>,
	'Michel Lespinasse' <walken@...gle.com>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	Martin Bligh <Martin.Bligh@...sigma.com>,
	Trammell Hudson <Trammell.Hudson@...sigma.com>,
	Christos Zoulas <Christos.Zoulas@...sigma.com>,
	"'linux-xfs@....sgi.com'" <linux-xfs@....sgi.com>,
	Stephen Degler <Stephen.Degler@...sigma.com>,
	"'linux-mm@...ck.org'" <linux-mm@...ck.org>
Subject: Re: XFS memory allocation deadlock in 2.6.38

On Tue, Mar 29, 2011 at 03:24:34PM -0400, 'Christoph Hellwig' wrote:
> Can you check if the brute force patch below helps?  If it does I
> still need to refine it a bit, but it could be that we are doing
> an allocation under an xfs lock that could recurse back into the
> filesystem.  We have a per-process flag to disable that for normal
> kmalloc allocation, but we lost it for vmalloc in the commit you
> bisected the regression to.
> 
> 
> Index: xfs/fs/xfs/linux-2.6/kmem.h
> ===================================================================
> --- xfs.orig/fs/xfs/linux-2.6/kmem.h	2011-03-29 21:16:58.039224236 +0200
> +++ xfs/fs/xfs/linux-2.6/kmem.h	2011-03-29 21:17:08.368223598 +0200
> @@ -63,7 +63,7 @@ static inline void *kmem_zalloc_large(si
>  {
>  	void *ptr;
>  
> -	ptr = vmalloc(size);
> +	ptr = __vmalloc(size, GFP_NOFS | __GFP_HIGHMEM, PAGE_KERNEL);
>  	if (ptr)
>  		memset(ptr, 0, size);
>  	return ptr;

Note that vmalloc is currently broken in that it does a GFP_KERNEL
allocation if it has to allocate page table pages, even when invoked
with GFP_NOFS:

	http://marc.info/?l=linux-mm&m=128942194520631&w=4

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