[tip:sched/core] sched/preempt, futex: Disable preemption in UP futex_atomic_cmpxchg_inatomic() explicitly

[tip-bot for David Hildenbrand]

Commit-ID:  d9b9ff8c18891d74dc7076800bde81b774f7d032
Gitweb:     http://git.kernel.org/tip/d9b9ff8c18891d74dc7076800bde81b774f7d032
Author:     David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 11 May 2015 17:52:14 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 19 May 2015 08:39:16 +0200

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 <tglx@xxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: David.Laight@xxxxxxxxxx
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: airlied@xxxxxxxx
Cc: akpm@xxxxxxxxxxxxxxxxxxxx
Cc: benh@xxxxxxxxxxxxxxxxxxx
Cc: bigeasy@xxxxxxxxxxxxx
Cc: borntraeger@xxxxxxxxxx
Cc: daniel.vetter@xxxxxxxxx
Cc: heiko.carstens@xxxxxxxxxx
Cc: herbert@xxxxxxxxxxxxxxxxxxx
Cc: hocko@xxxxxxx
Cc: hughd@xxxxxxxxxx
Cc: mst@xxxxxxxxxx
Cc: paulus@xxxxxxxxx
Cc: ralf@xxxxxxxxxxxxxx
Cc: schwidefsky@xxxxxxxxxx
Cc: yang.shi@xxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1431359540-32227-10-git-send-email-dahi@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 include/asm-generic/futex.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
index 3586017..e56272c 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;
 }
--
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