From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 11/13] x86/ticketlock: only do kick after doing unlock
Date: Fri, 02 Sep 2011 16:49:28 +0200
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References: <cover.1314922370.git.jeremy.fitzhardinge@citrix.com>
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To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Linus Torvalds <torvalds@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>, the arch/x86 maintainers <x86@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Nick Piggin <npiggin@kernel.dk>, Avi Kivity <avi@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, KVM <kvm@vger.kernel.org>, Andi Kleen <andi@firstfloor.org>, Xen Devel <xen-devel@lists.xensource.com>, Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>, Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
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On Thu, 2011-09-01 at 17:55 -0700, Jeremy Fitzhardinge wrote:
> From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
> 
> We must release the lock before checking to see if the lock is in
> slowpath or else there's a potential race where the lock enters the
> slow path after the unlocker has checked the slowpath flag, but before
> it has actually unlocked.
> 
> Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> 

Wouldn't it be much better to fold it back so that this bug never
happens when you bisect?