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From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
	Ingo Molnar <mingo@elte.hu>, "Rafael J. Wysocki" <rjw@sisk.pl>,
	Christian Kujau <lists@nerdbynature.de>,
	linux-kernel@vger.kernel.org,
	jfs-discussion@lists.sourceforge.net,
	Davide Libenzi <davidel@xmailserver.org>,
	Johannes Berg <johannes@sipsolutions.net>
Subject: Re: 2.6.24-rc6: possible recursive locking detected
Date: Sun, 13 Jan 2008 17:32:07 +0100	[thread overview]
Message-ID: <1200241927.7999.38.camel@lappy> (raw)
In-Reply-To: <20080107174908.GB14880@tv-sign.ru>


On Mon, 2008-01-07 at 20:49 +0300, Oleg Nesterov wrote:
> On 01/07, Oleg Nesterov wrote:
> >
> > Consider this "just for illustration" patch,
> > 
> > --- t/kernel/lockdep.c	2007-11-09 12:57:31.000000000 +0300
> > +++ t/kernel/lockdep.c	2008-01-07 19:43:50.000000000 +0300
> > @@ -1266,10 +1266,13 @@ check_deadlock(struct task_struct *curr,
> >  	struct held_lock *prev;
> >  	int i;
> >  
> > -	for (i = 0; i < curr->lockdep_depth; i++) {
> > +	for (i = curr->lockdep_depth; --i >= 0; ) {
> >  		prev = curr->held_locks + i;
> >  		if (prev->class != next->class)
> >  			continue;
> > +
> > +		if (prev->trylock == -1)
> > +			return 2;
> >  		/*
> >  		 * Allow read-after-read recursion of the same
> >  		 * lock class (i.e. read_lock(lock)+read_lock(lock)):
> > -------------------------------------------------------------------------
> > 
> > Now,
> > 
> > 	// trylock == -1
> > 	#define	spin_mark_nested(l)	\
> > 		lock_acquire(&(l)->dep_map, 0, -1, 0, 2, _THIS_IP_)
> > 	#define	spin_unmark_nested(l)	\
> > 		lock_release(&(l)->dep_map, 1, _THIS_IP_)
> > 
> > and ep_poll_safewake() can do:
> > 
> > 	/* Do really wake up now */
> > 	spin_mark_nested(&wq->lock);
> > 	wake_up(wq);
> > 	spin_unmark_nested(&wq->lock);
> 
> I tested the patch above with the following code,
> 
> 	wait_queue_head_t w1, w2, w3;
> 
> 	init_waitqueue_head(&w1);
> 	init_waitqueue_head(&w2);
> 	init_waitqueue_head(&w3);
> 
> 	local_irq_disable();
> 	spin_lock(&w1.lock);
> 
> 	spin_mark_nested(&w2.lock);
> 	spin_lock(&w2.lock);
> 
> 	spin_mark_nested(&w3.lock);
> 	wake_up(&w3);
> 	spin_unmark_nested(&w3.lock);
> 
> 	spin_unlock(&w2.lock);
> 	spin_unmark_nested(&w2.lock);
> 
> 	spin_unlock(&w1.lock);
> 	local_irq_enable();
> 
> seems to work. What do you think?

I've been pondering this for a while, and some days I really like it,
some days I don't.

The problem I have with it is that it becomes very easy to falsely
annotate problems away - its a very powerful annotation. That said, its
almost powerful enough to annotate the device semaphore/mutex problem.

I think I'll do wake_up_nested() for now and keep this around.

Thanks for this very nice idea though.


  reply	other threads:[~2008-01-13 16:32 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-03 22:58 Christian Kujau
2008-01-03 23:06 ` Rafael J. Wysocki
2008-01-04  8:30   ` Ingo Molnar
2008-01-05  7:12     ` Herbert Xu
2008-01-05 16:53       ` Peter Zijlstra
2008-01-05 17:01         ` Peter Zijlstra
2008-01-05 21:35           ` Davide Libenzi
2008-01-06  0:20             ` Christian Kujau
2008-01-07 21:35               ` Davide Libenzi
2008-01-06 21:44             ` Cyrill Gorcunov
2008-01-06 21:53               ` Cyrill Gorcunov
2008-01-07 17:22           ` Oleg Nesterov
2008-01-07 17:49             ` Oleg Nesterov
2008-01-13 16:32               ` Peter Zijlstra [this message]
2008-01-14 21:27                 ` Oleg Nesterov
2008-01-30 10:34                   ` hrtimers and lockdep (was: Re: 2.6.24-rc6: possible recursive locking detected) Peter Zijlstra
2008-01-30 17:36                     ` Thomas Gleixner

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