linux-kernel - Re: [stable] [PATCH] mm: prevent concurrent unmap_mapping

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Date:	Fri, 8 Jul 2011 09:26:49 +0800
From:	Wengang Wang <wen.gang.wang@...cle.com>
To:	Greg KH <greg@...ah.com>
Cc:	Wengang Wang <wen.gang.wang@...cle.com>, stable@...nel.org,
	greg.marsden@...cle.com, joe.jin@...cle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [stable] [PATCH] mm: prevent concurrent unmap_mapping_range() on
 the same inode --to stable

Hi, greg k-h

On 11-07-07 16:55, Greg KH wrote:
> On Fri, Jun 24, 2011 at 03:02:08PM +0800, Wengang Wang wrote:
> >         mainline commit 2aa15890f3c191326678f1bd68af61ec6b8753ec
> > 
> >     mm: prevent concurrent unmap_mapping_range() on the same inode
> > 
> >     Michael Leun reported that running parallel opens on a fuse filesystem
> >     can trigger a "kernel BUG at mm/truncate.c:475"
> > 
> >     Gurudas Pai reported the same bug on NFS.
> > 
> >     The reason is, unmap_mapping_range() is not prepared for more than
> >     one concurrent invocation per inode.  For example:
> > 
> >       thread1: going through a big range, stops in the middle of a vma and
> >          stores the restart address in vm_truncate_count.
> > 
> >       thread2: comes in with a small (e.g. single page) unmap request on
> >          the same vma, somewhere before restart_address, finds that the
> >          vma was already unmapped up to the restart address and happily
> >          returns without doing anything.
> > 
> >     Another scenario would be two big unmap requests, both having to
> >     restart the unmapping and each one setting vm_truncate_count to its
> >     own value.  This could go on forever without any of them being able to
> >     finish.
> > 
> >     Truncate and hole punching already serialize with i_mutex.  Other
> >     callers of unmap_mapping_range() do not, and it's difficult to get
> >     i_mutex protection for all callers.  In particular ->d_revalidate(),
> >     which calls invalidate_inode_pages2_range() in fuse, may be called
> >     with or without i_mutex.
> > 
> >     This patch adds a new mutex to 'struct address_space' to prevent
> >     running multiple concurrent unmap_mapping_range() on the same mapping.
> > 
> >     [ We'll hopefully get rid of all this with the upcoming mm
> >       preemptibility series by Peter Zijlstra, the "mm: Remove i_mmap_mutex
> >       lockbreak" patch in particular.  But that is for 2.6.39 ]
> > 
> > 
> >     Adding this patch causes Kabi breakage.
> > 
> >     Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
> >     Reported-by: Michael Leun <lkml20101129@...ton.leun.net>
> >     Reported-by: Gurudas Pai <gurudas.pai@...cle.com>
> >     Tested-by: Gurudas Pai <gurudas.pai@...cle.com>
> >     Acked-by: Hugh Dickins <hughd@...gle.com>
> >     Cc: stable@...nel.org
> >     Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> >     Signed-off-by: Wengang Wang <wen.gang.wang@...cle.com>
> 
> As this patch showed up in 2.6.39, I'm confused as to what you wanted me
> to do with it, so I've dropped it from my queue.

I hope this committed in 2.6.32 stable tree please.

regards,
wengang.
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