From: Andi Kleen <ak@suse.de>
To: Suleiman Souhlal <ssouhlal@freebsd.org>
Subject: Re: [PATCH] Fix x86_64 _spin_lock_irqsave()
Date: Thu, 24 Aug 2006 13:32:40 +0200
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Cc: Edward Falk <efalk@google.com>, linux-kernel@vger.kernel.org
References: <44ED157D.6050607@google.com> <p7364gifx8o.fsf@verdi.suse.de> <44ED87AC.8070106@FreeBSD.org>
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On Thursday 24 August 2006 13:04, Suleiman Souhlal wrote:
> Andi Kleen wrote:
> > Edward Falk <efalk@google.com> writes:
> > 
> > 
> >>Add spin_lock_string_flags and _raw_spin_lock_flags() to
> >>asm-x86_64/spinlock.h so that _spin_lock_irqsave() has the same
> >>semantics on x86_64 as it does on i386 and does *not* have interrupts
> >>disabled while it is waiting for the lock.
> > 
> > 
> > Did it fix anything for you?
> 
> I think this was to work around the fact that some buggy drivers try to 
> grab spinlocks without disabling interrupts when they should, which 
> would cause deadlocks when trying to rendez-vous every cpu via IPIs.

That doesn't help them at all because they could then deadlock later.

In theory it is just a quite cheesy way to make lock contended code
work a little better, but I was not aware of it actually helping 
in practice.

-Andi


> 
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