linux-kernel - Re: [PATCH] mm: rcu-protected get_mm_exe

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Date:	Mon, 16 Mar 2015 10:04:08 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:	Oleg Nesterov <oleg@...hat.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] mm: rcu-protected get_mm_exe_file()

On Mon, 2015-03-16 at 19:18 +0300, Konstantin Khlebnikov wrote:
> On 16.03.2015 17:50, Davidlohr Bueso wrote:
> > On Mon, 2015-03-16 at 15:07 +0100, Oleg Nesterov wrote:
> >> 	3. and we can remove down_write(mmap_sem) from prctl paths.
> >>
> >> 	   Actually we can do this even without xchg() above, but we might
> >> 	   want to kill MMF_EXE_FILE_CHANGED and test_and_set_bit() check.
> >
> > Yeah I was waiting for security folks input about this, otherwise this
> > still doesn't do it for me as we still have to deal with mmap_sem.
> >
> 
> Why? mm->flags are updated atomically. mmap_sem isn't required here.

Right, nm I was thinking of the set but Oleg's xchg() idea is obviously
correct and a much better approach to mine. The only thing I'd suggest
is explicitly commenting the lockless get_mm_exe_file callers, if
useful, you can take it from my patch 1.

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