Re: [PATCH] mm: fix overly aggressive shmdt() when calls span multiple segments

[Davidlohr Bueso]

On Mon, 2014-11-03 at 16:06 -0800, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> 
> This is a highly-contrived scenario.  But, a single shmdt() call
> can be induced in to unmapping memory from mulitple shm segments.
> Example code is here:
> 
> 	http://www.sr71.net/~dave/intel/shmfun.c
> 
> The fix is pretty simple:  Record the 'struct file' for the first
> VMA we encounter and then stick to it.  Decline to unmap anything
> not from the same file and thus the same segment.
> 
> I found this by inspection and the odds of anyone hitting this in
> practice are pretty darn small.
> 
> Lightly tested, but it's a pretty small patch.

Passed shmdt ltp tests, fwiw.

> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>

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