linux-kernel - [PATCH 1/3] futex: do not pagefault_disable in futex_atomic_cmpxchg

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Date:	Thu, 10 Mar 2011 18:47:31 -0800
From:	Michel Lespinasse <walken@...gle.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Darren Hart <darren@...art.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Matt Turner <mattst88@...il.com>,
	Russell King <linux@....linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Michal Simek <monstr@...str.eu>,
	Ralf Baechle <ralf@...ux-mips.org>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Metcalf <cmetcalf@...era.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/3] futex: do not pagefault_disable in
 futex_atomic_cmpxchg_inatomic()

kernel/futex.c disables page faults before calling
futex_atomic_cmpxchg_inatomic(), so there is no need to do it again
within that function.
    
Signed-off-by: Michel Lespinasse <walken@...gle.com>

diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
index b33fe70..7133a86 100644
--- a/arch/arm/include/asm/futex.h
+++ b/arch/arm/include/asm/futex.h
@@ -95,7 +95,8 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
 	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
 		return -EFAULT;
 
-	pagefault_disable();	/* implies preempt_disable() */
+	/* Note that preemption is disabled by futex_atomic_cmpxchg_inatomic
+	 * call sites. */
 
 	__asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
 	"1:	" T(ldr) "	%0, [%3]\n"
@@ -115,8 +116,6 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
 	: "r" (oldval), "r" (newval), "r" (uaddr), "Ir" (-EFAULT)
 	: "cc", "memory");
 
-	pagefault_enable();	/* subsumes preempt_enable() */
-
 	return val;
 }
 
-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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