[PATCH v1 10/15] arm/futex: UP futex_atomic_cmpxchg_inatomic() relies on disabled preemption

David Hildenbrand
2015-05-11T15:55:01Z

The !CONFIG_SMP implementation of futex_atomic_cmpxchg_inatomic()
requires preemption to be disabled to guarantee mutual exclusion.
Let's make this explicit.

This patch is based on a patch by Sebastian Andrzej Siewior on the
-rt branch.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
---
arch/arm/include/asm/futex.h | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
index 4e78065..255bfd1 100644
--- a/arch/arm/include/asm/futex.h
+++ b/arch/arm/include/asm/futex.h
@@ -93,6 +93,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
return -EFAULT;

+ preempt_disable();
__asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
"1: " TUSER(ldr) " %1, [%4]\n"
" teq %1, %2\n"
@@ -104,6 +105,8 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
: "cc", "memory");

*uval = val;
+ preempt_enable();
+
return ret;
}

--
2.1.4