This is a note to let you know that I have just added a patch titled
asm-generic/futex: Re-enable preemption in futex_atomic_cmpxchg_inatomic()
to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue
This patch is scheduled to be released in version 4.2.8-ckt9.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
---8<------------------------------------------------------------
>From cdfad9ed4667dcd1c50611495db26b59ebab1dd5 Mon Sep 17 00:00:00 2001
From: Romain Perier <romain.perier@xxxxxxxxxxxxxxxxxx>
Date: Thu, 14 Apr 2016 15:36:03 +0200
Subject: asm-generic/futex: Re-enable preemption in
futex_atomic_cmpxchg_inatomic()
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@xxxxxxxxxxxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1460640963-690-1-git-send-email-romain.perier@xxxxxxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
include/asm-generic/futex.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
index e56272c..bf2d34c 100644
--- a/include/asm-generic/futex.h
+++ b/include/asm-generic/futex.h
@@ -108,11 +108,15 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
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();
--
2.7.4
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