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authorMikael Pettersson <mikpe@it.uu.se>2011-08-15 10:11:50 +0000
committerGreg Kroah-Hartman <gregkh@suse.de>2011-10-03 11:39:59 -0700
commit7fe1e169829030a8257be59636f82c45753ca941 (patch)
tree1e24f9473aa728b65b5ddfbfa5956db22a6ee52a /arch/sparc
parentb60c440fff5c9e6dd8d328617b79b7fd57aed9b1 (diff)
sparc32: unbreak arch_write_unlock()
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 <mikpe@it.uu.se> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'arch/sparc')
-rw-r--r--arch/sparc/include/asm/spinlock_32.h11
1 files changed, 9 insertions, 2 deletions
diff --git a/arch/sparc/include/asm/spinlock_32.h b/arch/sparc/include/asm/spinlock_32.h
index 5f5b8bf3f50d..bcc98fc35281 100644
--- 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_rwlock_t *rw)
*(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(arch_rwlock_t *rw)
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)