linux-kernel - Re: linux 4.1-rc7 deadlock

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Date:	Sun, 14 Jun 2015 09:44:22 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Prarit Bhargava <prarit@...hat.com>
cc:	Hugh Dickins <hughd@...gle.com>,
	Morten Stevens <mstevens@...oraproject.org>,
	Daniel Wagner <wagi@...om.org>,
	Dave Chinner <david@...morbit.com>,
	Eric Paris <eparis@...hat.com>,
	Eric Sandeen <esandeen@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: linux 4.1-rc7 deadlock

On Thu, 11 Jun 2015, Prarit Bhargava wrote:
> On 06/11/2015 04:06 PM, Hugh Dickins wrote:
> > On Tue, 9 Jun 2015, Morten Stevens wrote:
> >> 2015-06-09 16:10 GMT+02:00 Daniel Wagner <wagi@...om.org>:
> >>> On 06/09/2015 01:54 PM, Morten Stevens wrote:
> > 
> > Reported-by: Prarit Bhargava <prarit@...hat.com>
> > Reported-by: Daniel Wagner <wagi@...om.org>
> > Reported-by: Morten Stevens <mstevens@...oraproject.org>
> > Not-Yet-Signed-off-by: Hugh Dickins <hughd@...gle.com>
> > ---
> > 
> >  mm/shmem.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > --- 4.1-rc7/mm/shmem.c	2015-04-26 19:16:31.352191298 -0700
> > +++ linux/mm/shmem.c	2015-06-11 11:08:21.042745594 -0700
> > @@ -3401,7 +3401,7 @@ int shmem_zero_setup(struct vm_area_stru
> >  	struct file *file;
> >  	loff_t size = vma->vm_end - vma->vm_start;
> >  
> > -	file = shmem_file_setup("dev/zero", size, vma->vm_flags);
> > +	file = __shmem_file_setup("dev/zero", size, vma->vm_flags, S_PRIVATE);
> 
> Perhaps,
> 
> 	file = shmem_kernel_file_setup("dev/zero", size, vma->vm_flags) ?

Perhaps.  I couldn't decide whether this is a proper intended use of
shmem_kernel_file_setup(), or a handy reuse of its flag.  Andrew asked
for a comment, so in the end I left that line as is, but refer to
shmem_kernel_file_setup() in the comment.  And that forced me to look a
little closer at the security implications: but we do seem to be safe.

> 
> Tested-by: Prarit Bhargava <prarit@...hat.com>

Thank you: I had been hoping for some corroboration from one of the other
guys (no offence to you, but 33% looks a bit weak!), but now it's Sunday
so I think I'd better send this off in the hope that it makes -rc8.

Hugh

> 
> P.
> 
> >  	if (IS_ERR(file))
> >  		return PTR_ERR(file);
--
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