Commit 1f49a2c2 authored Aug 15, 2008 by Mathieu Desnoyers Committed by H. Peter Anvin Aug 15, 2008

x86: revert replace LOCK_PREFIX in futex.h

Since we now use DS prefixes instead of NOP to remove LOCK prefixes,
there are no longer any issues with instruction boundaries moving around.

Depends on :

x86 alternatives : fix LOCK_PREFIX race with preemptible kernel and CPU hotplug

On Thu, 14 Aug 2008, Mathieu Desnoyers wrote:
>
> Changing the 0x90 (single-byte nop) currently used into a 0x3E DS segment
> override prefix should fix this issue. Since the default of the atomic
> instructions is to use the DS segment anyway, it should not affect the
> behavior.

Ok, so I think this is an _excellent_ patch, but I'd like to also then use
LOCK_PREFIX in include/asm-x86/futex.h.

See commit 9d55b992.

                Linus

Applies to 2.6.27-rc2 (and -rc3 unless hell broke loose in futex.h between rc2
and rc3).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: H. Peter Anvin <hpa@zytor.com>
CC: Jeremy Fitzhardinge <jeremy@goop.org>
CC: Roland McGrath <roland@redhat.com>
CC: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
CC: Steven Rostedt <srostedt@redhat.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: David Miller <davem@davemloft.net>
CC: Ulrich Drepper <drepper@redhat.com>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Gregory Haskins <ghaskins@novell.com>
CC: Arnaldo Carvalho de Melo <acme@redhat.com>
CC: "Luis Claudio R. Goncalves" <lclaudio@uudg.org>
CC: Clark Williams <williams@redhat.com>
CC: Christoph Lameter <cl@linux-foundation.org>
CC: Andi Kleen <andi@firstfloor.org>
CC: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

parent f88f07e0

include/asm-x86/futex.h

+3 −3

Original line number	Diff line number	Diff line
		@@ -25,7 +25,7 @@
		asm volatile("1:\tmovl %2, %0\n" \
		"\tmovl\t%0, %3\n" \
		"\t" insn "\n" \
		"2:\tlock; cmpxchgl %3, %2\n" \
		"2:\t" LOCK_PREFIX "cmpxchgl %3, %2\n" \
		"\tjnz\t1b\n" \
		"3:\t.section .fixup,\"ax\"\n" \
		"4:\tmov\t%5, %1\n" \
		@@ -64,7 +64,7 @@ static inline int futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
		__futex_atomic_op1("xchgl %0, %2", ret, oldval, uaddr, oparg);
		break;
		case FUTEX_OP_ADD:
		__futex_atomic_op1("lock; xaddl %0, %2", ret, oldval,
		__futex_atomic_op1(LOCK_PREFIX "xaddl %0, %2", ret, oldval,
		uaddr, oparg);
		break;
		case FUTEX_OP_OR:
		@@ -122,7 +122,7 @@ static inline int futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval,
		if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
		return -EFAULT;

		asm volatile("1:\tlock; cmpxchgl %3, %1\n"
		asm volatile("1:\t" LOCK_PREFIX "cmpxchgl %3, %1\n"
		"2:\t.section .fixup, \"ax\"\n"
		"3:\tmov %2, %0\n"
		"\tjmp 2b\n"

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