linux-kernel - Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM

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Date:	Fri, 30 Jan 2009 17:40:24 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Greg KH <gregkh@...e.de>,
	Maksim Yevmenkin <maksim.yevmenkin@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	will@...wder-design.com, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED
 file segments

On Fri, 30 Jan 2009, Linus Torvalds wrote:
> On Thu, 29 Jan 2009, Greg KH wrote:
> > 
> > Which version was the "non-cleanup" version that should be added to the
> > stable trees?
> 
> There were two different versions:
> 
> 	From: Andrew Morton <akpm@...ux-foundation.org>
> 	Subject: Re: possible bug in mmap_region() in linux-2.6.28 kernel
> 	Message-Id: <20090128134350.034ac6a7.akpm@...ux-foundation.org>
> 
> 	From: Lee Schermerhorn <Lee.Schermerhorn@...com>
> 	Subject: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments
> 	Message-Id: <1233259410.2315.75.camel@...-notebook>
> 
> and I'm actually not at all sure which one should go into stable (or if we 
> should just pick the same one that went into mainline). 
> 
...
> 
> But none of the above really changes the fact that the patch I committed 
> to mainline was really quite fundamentally more invasive than either of 
> the "simple" patches. All three patches are small, with mine arguably the 
> smallest of the lot, but mine actually changed semantics, while Andrew's 
> and Lee's patch literally only fix the invalid pointer use.
> 
> I'll leave it to others to decide which one goes into -stable. I 
> personally don't really think it matters. I argue above that mine is 
> pretty safe and thus perfectly fine even for -stable, but reality has a 
> habit of sometimes disagreeing with me. Dang.

I'd say one of the non-cleanup versions for -stable
(but I've not compared them to see which one is better).

I'm still working my way through all the ->mmap methods to check
their safety with regard to yesterday's change (there are about
ten times as many as the last time I looked).  So far there's only
one driver mmap I want to go back and recheck, the vast majority
are as good today as they were the day before, but ...

... what I think you have done is break the vma merging on
ordinary files: because of that irritating VM_CAN_NONLINEAR
flag which generic_file_mmap() and some others add in.

To break the merging won't cause anyone much trouble,
but is a slight regression we should fix.

I'd have been very upset not to find something ;)

Hugh
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