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From: Peter Zijlstra <peterz@infradead.org>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Linux Kernel list <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH 1/2] lockdep: implement full check without irq checking
Date: Wed, 29 Oct 2008 16:23:16 +0100	[thread overview]
Message-ID: <1225293796.9315.4.camel@lappy.programming.kicks-ass.net> (raw)
In-Reply-To: <1224791072.6002.63.camel@johannes.berg>

On Thu, 2008-10-23 at 21:44 +0200, Johannes Berg wrote: 
> This patch implements a new check type "3" which means "full validation
> but without irq tracing" in order to allow some certain fake locks that
> are only added for deadlock detection to not cause inconsistent state
> warnings which would be inappropriate for them.

This thing worries me, can you help my exhausted brain a long a little..

So I take it the idea is to couple the lock chains of the site calling
del_timer_sync and the actual timer.

We do this by holding a fake lock while executing the timer, so that its
lock chain starts with that lock.

We then acquire the fake lock on del_timer_sync so as to establish a
relation.

Now you get warnings about using a lock in hardirq context that was
previously used !irq-safe, right?

So why not simply write something like:


del_timer_sync():

  local_irq_save(flags);
  lock_aquire(my fake timer lock);
  lock_release(...);
  local_irq_restore(flags);

and make that conditional CONFIG_PROVE_LOCKING and or wrap it up
somewhere..




  reply	other threads:[~2008-10-29 18:03 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-23 19:35 [PATCH 0/2] Timer sync lock checking Johannes Berg
2008-10-23 19:44 ` [PATCH 1/2] lockdep: implement full check without irq checking Johannes Berg
2008-10-29 15:23   ` Peter Zijlstra [this message]
2008-10-30 10:36     ` Johannes Berg
2008-10-30 11:15       ` Peter Zijlstra
2008-10-30 11:25         ` Johannes Berg
2008-10-23 19:46 ` [PATCH 2/2] timer: implement lockdep deadlock detection Johannes Berg
2008-10-23 20:37 ` [PATCH 3/2] tasklet: " Johannes Berg

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