linux-kernel - Re: lockdep oddity

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Message-ID: <20060906100507.GA12799@elte.hu>
Date:	Wed, 6 Sep 2006 12:05:07 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Daniel Walker <dwalker@...sta.com>,
	Hua Zhong <hzhong@...il.com>
Subject: Re: lockdep oddity


* Heiko Carstens <heiko.carstens@...ibm.com> wrote:

> That seems to be code that isn't upstream. 2.6.18-rc5-mm1 as well as 
> Linus' current git tree have this:
> 
> /*
>  * If lockdep is enabled then we use the non-preemption spin-ops
>  * even on CONFIG_PREEMPT, because lockdep assumes that interrupts are
>  * not re-enabled during lock-acquire (which the preempt-spin-ops do):
>  */
> #if !defined(CONFIG_PREEMPT) || !defined(CONFIG_SMP) || \
>         defined(CONFIG_PROVE_LOCKING)
> 
> And yes, using CONFIG_DEBUG_LOCK_ALLOC instead of CONFIG_PROVE_LOCKING 
> fixes this for me :)

indeed, this is a very recent fix from Jarek Poplawski - not yet in 
Linus' tree but already in Andrew's.

	Ingo

---------->
From: Jarek Poplawski <jarkao2@...pl>

With

CONFIG_SMP=y
CONFIG_PREEMPT=y
CONFIG_LOCKDEP=y
CONFIG_DEBUG_LOCK_ALLOC=y
# CONFIG_PROVE_LOCKING is not set

spin_unlock_irqrestore() goes through lockdep but spin_lock_irqsave() doesn't.
Apparently, bad things happen.

Acked-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Andrew Morton <akpm@...l.org>
---

 kernel/spinlock.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN kernel/spinlock.c~lockdep-ifdef-fix kernel/spinlock.c
--- a/kernel/spinlock.c~lockdep-ifdef-fix
+++ a/kernel/spinlock.c
@@ -72,7 +72,7 @@ EXPORT_SYMBOL(_write_trylock);
  * not re-enabled during lock-acquire (which the preempt-spin-ops do):
  */
 #if !defined(CONFIG_PREEMPT) || !defined(CONFIG_SMP) || \
-	defined(CONFIG_PROVE_LOCKING)
+	defined(CONFIG_DEBUG_LOCK_ALLOC)
 
 void __lockfunc _read_lock(rwlock_t *lock)
 {
_
-
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