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From: Andrew Morton <akpm@linux-foundation.org>
To: Hugh Dickins <hugh@veritas.com>
Cc: Matt Mackall <mpm@selenic.com>, Alexey Dobriyan <adobriyan@sw.ru>,
	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
Date: Fri, 27 Apr 2007 22:48:44 -0700	[thread overview]
Message-ID: <20070427224844.8d6d5503.akpm@linux-foundation.org> (raw)
In-Reply-To: <Pine.LNX.4.64.0704280607330.9554@blonde.wat.veritas.com>

On Sat, 28 Apr 2007 06:13:39 +0100 (BST) Hugh Dickins <hugh@veritas.com> wrote:

> 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.
> 

Yes.  lockdep has a way of working out if this task already has a
particular lock for reading or writing, but it isn't immediately obvious
how to extract that.

I guess a simple hack would be do do a down_read() on it.  If it's already
held for reading, lockdep should warn.  If it's already held for writing
someone will notice.

Oh well, it's not my top priority.

      reply	other threads:[~2007-04-28  5:50 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <200704270814.l3R8EnFJ023047@shell0.pdx.osdl.net>
2007-04-27 10:45 ` Alexey Dobriyan
2007-04-27 20:27   ` Andrew Morton
2007-04-27 20:41     ` Matt Mackall
2007-04-27 21:31       ` Andrew Morton
2007-04-28  5:13         ` Hugh Dickins
2007-04-28  5:48           ` Andrew Morton [this message]

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