linux-kernel - [PATCH RFC 10/15] arm/futex: UP futex_atomic_cmpxchg

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Date:	Wed,  6 May 2015 19:50:34 +0200
From:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	dahi@...ux.vnet.ibm.com, mingo@...hat.com, peterz@...radead.org,
	yang.shi@...driver.com, bigeasy@...utronix.de,
	benh@...nel.crashing.org, paulus@...ba.org,
	akpm@...ux-foundation.org, heiko.carstens@...ibm.com,
	schwidefsky@...ibm.com, borntraeger@...ibm.com, mst@...hat.com,
	tglx@...utronix.de, David.Laight@...LAB.COM, hughd@...gle.com,
	hocko@...e.cz, ralf@...ux-mips.org, herbert@...dor.apana.org.au,
	linux@....linux.org.uk, airlied@...ux.ie, daniel.vetter@...el.com,
	linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: [PATCH RFC 10/15] arm/futex: UP futex_atomic_cmpxchg_inatomic() relies on disabled preemption

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.

Signed-off-by: David Hildenbrand <dahi@...ux.vnet.ibm.com>
---
 arch/arm/include/asm/futex.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
index 4e78065..255bfd1 100644
--- a/arch/arm/include/asm/futex.h
+++ b/arch/arm/include/asm/futex.h
@@ -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;
 }
 
-- 
2.1.4

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