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

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

[gregkh]

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 <stable@vger.kernel.org> know about it.


>From fba7cd681b6155e2d93e7862fcd6f970336b83c3 Mon Sep 17 00:00:00 2001
From: Romain Perier <romain.perier@free-electrons.com>
Date: Thu, 14 Apr 2016 15:36:03 +0200
Subject: asm-generic/futex: Re-enable preemption in futex_atomic_cmpxchg_inatomic()

From: Romain Perier <romain.perier@free-electrons.com>

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 ]

Fixes: d9b9ff8c1889 ("sched/preempt, futex: Disable preemption in UP futex_atomic_cmpxchg_inatomic() explicitly")
Signed-off-by: Romain Perier <romain.perier@free-electrons.com>
Cc: linux-arch@vger.kernel.org
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1460640963-690-1-git-send-email-romain.perier@free-electrons.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/include/asm-generic/futex.h
+++ b/include/asm-generic/futex.h
@@ -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 romain.perier@free-electrons.com are

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