linux-kernel - [PATCH] slub: Fix the lockless code on 32-bit platforms with no 64-bit cmpxchg

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Date:	Wed, 4 May 2011 16:36:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Tejun Heo <tj@...nel.org>, Pekka Enberg <penberg@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	werner <w.landgraf@...ru>, "H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>
Subject: [PATCH] slub: Fix the lockless code on 32-bit platforms with no
 64-bit cmpxchg


* Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > Patch below. Ingo, can you test that please ?
> 
> Sure - test underway.

Ok, the patch below is looking really good - the test would have crashed on the 
bad kernel. I think we can consider the regression fixed:

  Acked-and-tested-by: Ingo Molnar <mingo@...e.hu>

I'll keep it running some more to make really sure it's fixed, plus it would be 
nice if Walter tested your fix as well.

Thanks,

	Ingo

----------------->
>From c22bd309573330e33a77c329405d9473fc14f1cb Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@...utronix.de>
Date: Wed, 4 May 2011 15:38:19 +0200
Subject: [PATCH] slub: Fix the lockless code on 32-bit platforms with no 64-bit cmpxchg

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Pekka Enberg <penberg@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: werner <w.landgraf@...ru>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Tejun Heo <tj@...nel.org>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1105041539050.3005@ionos
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 include/linux/percpu.h |    2 +-
 mm/slub.c              |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 3a5c444..8b97308 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -948,7 +948,7 @@ do {									\
 	irqsafe_generic_cpu_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2)
 # endif
 # define irqsafe_cpu_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2)	\
-	__pcpu_double_call_return_int(irqsafe_cpu_cmpxchg_double_, (pcp1), (pcp2), (oval1), (oval2), (nval1), (nval2))
+	__pcpu_double_call_return_bool(irqsafe_cpu_cmpxchg_double_, (pcp1), (pcp2), (oval1), (oval2), (nval1), (nval2))
 #endif
 
 #endif /* __LINUX_PERCPU_H */
diff --git a/mm/slub.c b/mm/slub.c
index 94d2a33..9d2e5e4 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1940,7 +1940,7 @@ redo:
 		 * Since this is without lock semantics the protection is only against
 		 * code executing on this cpu *not* from access by other cpus.
 		 */
-		if (unlikely(!this_cpu_cmpxchg_double(
+		if (unlikely(!irqsafe_cpu_cmpxchg_double(
 				s->cpu_slab->freelist, s->cpu_slab->tid,
 				object, tid,
 				get_freepointer(s, object), next_tid(tid)))) {
@@ -2145,7 +2145,7 @@ redo:
 		set_freepointer(s, object, c->freelist);
 
 #ifdef CONFIG_CMPXCHG_LOCAL
-		if (unlikely(!this_cpu_cmpxchg_double(
+		if (unlikely(!irqsafe_cpu_cmpxchg_double(
 				s->cpu_slab->freelist, s->cpu_slab->tid,
 				c->freelist, tid,
 				object, next_tid(tid)))) {
--
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