Commit 39919b01 authored May 11, 2015 by David Hildenbrand Committed by Ingo Molnar May 19, 2015

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: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>

parent d9b9ff8c

arch/arm/include/asm/futex.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -93,6 +93,7 @@ futex_atomic_cmpxchg_inatomic(u32 uval, u32 __user uaddr,
		if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
		return -EFAULT;

		preempt_disable();
		__asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
		"1: " TUSER(ldr) " %1, [%4]\n"
		" teq %1, %2\n"
		@@ -104,6 +105,8 @@ futex_atomic_cmpxchg_inatomic(u32 uval, u32 __user uaddr,
		: "cc", "memory");

		*uval = val;
		preempt_enable();

		return ret;
		}