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Commit 8b57184f authored by Sami Tolvanen's avatar Sami Tolvanen Committed by Amit Pundir
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BACKPORT: sched/preempt, arm/futex: Disable preemption in UP... 


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

The !CONFIG_SMP implementation of futex_atomic_cmpxchg_inatomic()
requires preemption to be disabled to guarantee mutual exclusion.
Let's make this explicit.

This patch is based on a patch by Sebastian Andrzej Siewior on the
-rt branch.

Reviewed-and-tested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarDavid Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: airlied@linux.ie
Cc: akpm@linux-foundation.org
Cc: benh@kernel.crashing.org
Cc: bigeasy@linutronix.de
Cc: borntraeger@de.ibm.com
Cc: daniel.vetter@intel.com
Cc: heiko.carstens@de.ibm.com
Cc: herbert@gondor.apana.org.au
Cc: hocko@suse.cz
Cc: hughd@google.com
Cc: mst@redhat.com
Cc: paulus@samba.org
Cc: ralf@linux-mips.org
Cc: schwidefsky@de.ibm.com
Cc: yang.shi@windriver.com
Link: http://lkml.kernel.org/r/1431359540-32227-11-git-send-email-dahi@linux.vnet.ibm.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>

Change-Id: Ia3f2177a38b29e9d521d2f79d2b19e4d721cd0c2
(cherry picked from commit 39919b01ae4c1949736b40b79e27178d0c0bc406)
Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
parent d36d017d

arch/arm/include/asm/futex.h

+4 −0
Original line number Diff line number Diff line
@@ -106,6 +106,8 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, 
	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))

		return -EFAULT;



	preempt_disable();

	__ua_flags = uaccess_save_and_enable();

	__asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"

	"1:	" TUSER(ldr) "	%1, [%4]\n"

	"	teq	%1, %2\n"
@@ -118,6 +120,8 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, 
	uaccess_restore(__ua_flags);



	*uval = val;

	preempt_enable();



	return ret;

}