Patch "asm-generic/futex: Re-enable preemption in futex_atomic_cmpxchg_inatomic()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

asm-generic/futex: Re-enable preemption in futex_atomic_cmpxchg_inatomic()

to the 4.4-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:
asm-generic-futex-re-enable-preemption-in-futex_atomic_cmpxchg_inatomic.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Romain Perier <[email protected]>
Date: Thu, 14 Apr 2016 15:36:03 +0200
Subject: asm-generic/futex: Re-enable preemption in futex_atomic_cmpxchg_inatomic()

From: Romain Perier <[email protected]>

commit fba7cd681b6155e2d93e7862fcd6f970336b83c3 upstream.

The recent decoupling of pagefault disable and preempt disable added an explicit preempt_disable/enable() pair to the futex_atomic_cmpxchg_inatomic() implementation in asm-generic/futex.h. But it forgot to add preempt_enable() calls to the error handling code pathes, which results in a preemption count imbalance.

This is observable on boot when the test for atomic_cmpxchg() is calling futex_atomic_cmpxchg_inatomic() on a NULL pointer.

Add the missing preempt_enable() calls to the error handling code pathes.

[ tglx: Massaged changelog ]

---
 include/asm-generic/futex.h |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

@@ -108,11 +108,15 @@ futex_atomic_cmpxchg_inatomic(u32 *uval,
 	u32 val;
 
 	preempt_disable();
-	if (unlikely(get_user(val, uaddr) != 0))
+	if (unlikely(get_user(val, uaddr) != 0)) {
+		preempt_enable();
 		return -EFAULT;
+	}
 
-	if (val == oldval && unlikely(put_user(newval, uaddr) != 0))
+	if (val == oldval && unlikely(put_user(newval, uaddr) != 0)) {
+		preempt_enable();
 		return -EFAULT;
+	}
 
 	*uval = val;
 	preempt_enable();

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/asm-generic-futex-re-enable-preemption-in-futex_atomic_cmpxchg_inatomic.patch