From: Ingo Molnar <mingo@elte.hu>
To: Christian Borntraeger <borntrae@de.ibm.com>
Cc: linux-kernel@vger.kernel.org,
Rusty Russell <rusty@rustcorp.com.au>,
Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@timesys.com>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Andrew Morton <akpm@osdl.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] bug in futex unqueue_me
Date: Mon, 31 Jul 2006 13:49:31 +0200 [thread overview]
Message-ID: <20060731114931.GA2003@elte.hu> (raw)
In-Reply-To: <200607311004.15878.borntrae@de.ibm.com>
* Christian Borntraeger <borntrae@de.ibm.com> wrote:
> On Sunday 30 July 2006 08:38, Ingo Molnar wrote:
> > interesting, how is this possible? We do a spin_lock(lock_ptr), and
> > taking a spinlock is an implicit barrier(). So gcc must not delay
> > evaluating lock_ptr to inside the critical section. And as far as i can
> > see the s390 spinlock implementation goes through an 'asm volatile'
> > piece of code, which is a barrier already. So how could this have
> > happened?
>
> spin_lock is a barrier, but isnt the barrierness too late here? The
> compiler reloads the value of lock_ptr after the "if(lock_ptr)" and
> *before* calling spin_lock(lock_ptr):
ah, indeed. So your patch is a real fix. Thanks,
Acked-by: Ingo Molnar <mingo@elte.hu>
Ingo
prev parent reply other threads:[~2006-07-31 11:56 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-27 16:41 [PATCH] bug in futex unqueue_me Christian Borntraeger
2006-07-30 6:38 ` Ingo Molnar
2006-07-30 23:53 ` Steven Rostedt
2006-07-31 8:04 ` Christian Borntraeger
2006-07-31 11:49 ` Ingo Molnar [this message]
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