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

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Date:	Thu, 7 Jul 2011 18:41:34 -0700
From:	Greg KH <greg@...ah.com>
To:	Wengang Wang <wen.gang.wang@...cle.com>
Cc:	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

On Fri, Jul 08, 2011 at 09:26:49AM +0800, Wengang Wang wrote:
> 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.

Ah, ok, care to resend this, with that information in it somewhere, so I
can do that?

thanks,

greg "I get a _lot_ of email" k-h
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