This is a note to let you know that I've just added the patch titled
sparc32: unbreak arch_write_unlock()
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sparc32-unbreak-arch_write_unlock.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <sta...@kernel.org> know about it.
>From 3f6aa0b113846a8628baa649af422cfc6fb1d786 Mon Sep 17 00:00:00 2001
From: Mikael Pettersson <mi...@it.uu.se>
Date: Mon, 15 Aug 2011 10:11:50 +0000
Subject: sparc32: unbreak arch_write_unlock()
From: Mikael Pettersson <mi...@it.uu.se>
commit 3f6aa0b113846a8628baa649af422cfc6fb1d786 upstream.
The sparc32 version of arch_write_unlock() is just a plain assignment.
Unfortunately this allows the compiler to schedule side-effects in a
protected region to occur after the HW-level unlock, which is broken.
E.g., the following trivial test case gets miscompiled:
#include <linux/spinlock.h>
rwlock_t lock;
int counter;
void foo(void) { write_lock(&lock); ++counter; write_unlock(&lock); }
Fixed by adding a compiler memory barrier to arch_write_unlock(). The
sparc64 version combines the barrier and assignment into a single asm(),
and implements the operation as a static inline, so that's what I did too.
Compile-tested with sparc32_defconfig + CONFIG_SMP=y.
Signed-off-by: Mikael Pettersson <mi...@it.uu.se>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@suse.de>
---
arch/sparc/include/asm/spinlock_32.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- a/arch/sparc/include/asm/spinlock_32.h
+++ b/arch/sparc/include/asm/spinlock_32.h
@@ -131,6 +131,15 @@ static inline void arch_write_lock(arch_
*(volatile __u32 *)&lp->lock = ~0U;
}
+static void inline arch_write_unlock(arch_rwlock_t *lock)
+{
+ __asm__ __volatile__(
+" st %%g0, [%0]"
+ : /* no outputs */
+ : "r" (lock)
+ : "memory");
+}
+
static inline int arch_write_trylock(arch_rwlock_t *rw)
{
unsigned int val;
@@ -175,8 +184,6 @@ static inline int __arch_read_trylock(ar
res; \
})
-#define arch_write_unlock(rw) do { (rw)->lock = 0; } while(0)
-
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
#define arch_read_lock_flags(rw, flags) arch_read_lock(rw)
#define arch_write_lock_flags(rw, flags) arch_write_lock(rw)
Patches currently in stable-queue which might be from mi...@it.uu.se are
queue-3.0/sparc64-remove-unnecessary-macros-from-spinlock_64.h.patch
queue-3.0/sparc32-unbreak-arch_write_unlock.patch
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