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

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Date:	Fri, 25 Aug 2006 08:21:44 +0200
From:	Andi Kleen <ak@...e.de>
To:	Andrew Morton <akpm@...l.org>
Cc:	Edward Falk <efalk@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix x86_64 _spin_lock_irqsave()

On Friday 25 August 2006 06:38, Andrew Morton wrote:
> On 24 Aug 2006 08:45:11 +0200
> Andi Kleen <ak@...e.de> 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?
> > 
> 
> It's the rendezvous-via-IPI problem.  Suppose we want to capture all CPUs
> in an IPI handler (TSC sync, for example).
> 
> - CPUa holds read_lock(&tasklist_lock)
> - CPUb is spinning in write_lock_irq(&taslist_lock)

But he didn't actually change the rwlocks, only the plain old spinlocks!

Anyways I applied the patch for now (and cleaned it up in the next patch), 
but I could have probably gotten away with not.

Edward, next time please add a Signed-off-by line.

-Andi
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