linux-kernel - Re: OOPS in perf_mmap

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Date:	Thu, 23 May 2013 17:24:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	trinity@...r.kernel.org
Subject: Re: OOPS in perf_mmap_close()

On Thu, May 23, 2013 at 02:09:10PM +0000, Christoph Lameter wrote:
> On Thu, 23 May 2013, Peter Zijlstra wrote:
> 
> > Right it doesn't. I think the easiest solution for now is to not copy the VMA
> > on fork().
> 
> Right. Pinned pages are not inherited. If a page is unpinned then that is
> going to happen for all address spaces that reference the page.
> 
> > But I totally missed patch bc3e53f682d that introduced pinned_vm, AFAICT that
> > also wrecked some accounting. We should still account both against
> > RLIMIT_MEMLOCK.
> 
> The point of the patch was to unwreck accounting. Before the patch mlocked
> pages were counted twice which resulted in stramge VM scenarios where more
> pages were mlocked than memory available. Note that a pinned page may also
> be mlocked.
> 
> Simply adding the two will reintroduce the problems that were fixed by the
> patch.

The patch completely fails to explain how RLIMIT_LOCKED is supposed to
deal with pinned vs locked. Perf used to account its pages against
RLIMIT_LOCKED, with the patch it compares pinned against RLIMIT_LOCKED
but completely discards any possible locked pages.

IMO that's broken.
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