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Date: Sat, 28 Apr 2007 06:13:39 +0100 (BST)
From: Hugh Dickins <hugh@veritas.com>
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To: Andrew Morton <akpm@linux-foundation.org>
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       linux-kernel@vger.kernel.org, Nick Piggin <nickpiggin@yahoo.com.au>
Subject: Re: - maps2-add-proc-pid-pagemap-interface-fix.patch removed from
 -mm tree
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On Fri, 27 Apr 2007, Andrew Morton wrote:
> 
> hm, could do.  might_sleep() is intertwined with preempt in complex ways,
> but we did decouple that at the config level.  no_mmap_sem() will dtrt for
> all preempt settings.
> 
> But I'll be keeping this as a -mm-only debug patch (which brings us up to
> about thirty of 'em), so I think it's best to make it unconfigurable so we
> get maximum coverage.
> 
> That's if it actually works.  I haven't tried running it yet, and I have a
> feeling that running it might cause a big "doh" moment.  We'll see.

Yes, I'm expecting the crucial

> +	WARN_ON(rwsem_is_locked(&mm->mmap_sem))

to give a bogus warning every time another thread (or /proc,
or swapoff, or whatever) happens to have this mmap_sem locked.
might_sleep() is quite different, works on our thread's info.

Hugh