linux-kernel - Re: [PATCH 3/8] x86/ticketlock: Use C for __ticket_spin

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Message-ID: <4E29CF51.60600@goop.org>
Date:	Fri, 22 Jul 2011 12:28:17 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 3/8] x86/ticketlock: Use C for __ticket_spin_unlock

On 07/22/2011 11:32 AM, H. Peter Anvin wrote:
> On 06/24/2011 03:41 PM, Jeremy Fitzhardinge wrote:
>> On 06/24/2011 02:52 PM, H. Peter Anvin wrote:
>>> These should be asm volatile, I believe.
>> OK.
>>
>>     J
> You still owe me a new patch here, I believe...

Ah, yes, though I don't think it can make a difference in practice,
since the caller contains barrier()s on either side.  And the non-asm
non-locked variant has no equivalent.  But it can't hurt.

    J

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Date: Fri, 22 Jul 2011 12:27:14 -0700
Subject: [PATCH] x86/ticketlocks: make asms volatile to be extra sure

Make the locked-unlock asms volatile, just to be extra sure they won't wander away.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 2d14e7c..05fd59e 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -36,11 +36,11 @@
 static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
 {
 	if (sizeof(lock->tickets.head) == sizeof(u8))
-		asm (LOCK_PREFIX "incb %0"
-		     : "+m" (lock->tickets.head) : : "memory");
+		asm volatile (LOCK_PREFIX "incb %0"
+			      : "+m" (lock->tickets.head) : : "memory");
 	else
-		asm (LOCK_PREFIX "incw %0"
-		     : "+m" (lock->tickets.head) : : "memory");
+		asm volatile (LOCK_PREFIX "incw %0"
+			      : "+m" (lock->tickets.head) : : "memory");
 
 }
 #else


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