sched/preempt, futex: Disable preemption in UP futex_atomic_cmpxchg_inatomic() explicitly

Let's explicitly disable/enable preemption in the !CONFIG_SMP version
of futex_atomic_cmpxchg_inatomic(), to prepare for pagefault_disable() not
touching preemption anymore. This is needed for this function to be
callable from both, atomic and non-atomic context.

Otherwise we might break mutual exclusion when relying on a get_user()/
put_user() implementation.

Reviewed-and-tested-by: Thomas Gleixner <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: [email protected]
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
index 358601750fe7..e56272c919b5 100644
--- a/include/asm-generic/futex.h
+++ b/include/asm-generic/futex.h
@@ -107,6 +107,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 {
 	u32 val;
 
+	preempt_disable();
 	if (unlikely(get_user(val, uaddr) != 0))
 		return -EFAULT;
 
@@ -114,6 +115,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 		return -EFAULT;
 
 	*uval = val;
+	preempt_enable();
 
 	return 0;
 }