linux-kernel - Re: [PATCH] Fix x86_64 _spin_lock

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Message-Id: <1156425718.3014.64.camel@laptopd505.fenrus.org>
Date:	Thu, 24 Aug 2006 15:21:58 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Suleiman Souhlal <ssouhlal@...eBSD.org>
Cc:	Andi Kleen <ak@...e.de>, Edward Falk <efalk@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix x86_64 _spin_lock_irqsave()

On Thu, 2006-08-24 at 14:33 +0200, Suleiman Souhlal wrote:
> Andi Kleen wrote:
> > On Thursday 24 August 2006 13:04, Suleiman Souhlal wrote:
> > 
> >>Andi Kleen wrote:
> >>
> >>>Edward Falk <efalk@...gle.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.
> 
> If the driver uses spin_lock() when it knows that the hardware won't 
> generate the interrupt that would need to be masked, and 
> spin_lock_irqsave() elsewhere, there shouldn't be any deadlocks unless 
> IPIs are involved.

this still is bad practice and lockdep will also scream about it

Can you point at ANY place that does this? 


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