linux-kernel - Re: [2.6.27-rc5] inotify_read's ev_mutex vs do_page_fault's mmap

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Message-Id: <1221040771.2442.120.camel@twins.programming.kicks-ass.net>
Date:	Wed, 10 Sep 2008 11:59:31 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Daniel J Blueman <daniel.blueman@...il.com>,
	torvalds@...ux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [2.6.27-rc5] inotify_read's ev_mutex vs do_page_fault's
 mmap_sem...

On Wed, 2008-09-10 at 19:50 +1000, Nick Piggin wrote:
> On Wednesday 10 September 2008 18:37, Ingo Molnar wrote:
> > * Nick Piggin <nickpiggin@...oo.com.au> wrote:
> > > On Wednesday 10 September 2008 17:57, Peter Zijlstra wrote:
> 
> > > > Sure, how about the below - untested - uncompiled, might eat kittens,
> > > > etc..
> > > >
> > > > Just sprinkle something like:
> > > >
> > > >   might_lock_read(&mm->mmap_sem);
> > > >
> > > > in the right places.
> > >
> > > Ahh, very nice, thanks! I'll give that a try...
> >
> > cool! Please send in an RFC patch once you have something that boots -
> > we can stick it into tip/core/locking and see whether there's any new
> > messages on a wide range of systems and workloads. (and we'd also check
> > whether the number of kittens is an invariant.)
> 
> Well I have verified it boots, and have used the annotation in some of
> x86-64's user copy routines (luckily no flood of bugs I was scared of,
> phew!)
> 
> So I would like to request you merge Peter's patch, and we'll hopefully
> start seeing the annotations being used. 

Will you send your x86_64 patch to be the first?

> FWIW, I don't suppose lockdep
> can determine that it is a sleeping lock, and do the appropriate
> might_sleep checks at this point as well?

Humm, no - we don't actually have that information there - I guess one
could add it to lockdep_map and set it from the various init routines,
but I'm not sure its worth it - just add might_sleep() along with
might_lock() :-)

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