Messages in this thread Patch in this message | | | Date | Thu, 7 Feb 2008 00:43:09 +0100 | From | Ingo Molnar <> | Subject | Re: [stable] The SMP alternatives code breaks exception fixup? |
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > I don't see this in Linus's tree, am I just missing it? Do you have > > a git commit id? > > Isn't this 9d55b9923a1b7ea8193b8875c57ec940dc2ff027 (possibly with > 2532ec6d178abc55681d049097d3dc577eaa266c on top)?
yeah.
Greg: note that this is against post-unification asm-x86/futex.h so it wont apply to .24.
I've backported the fix to .24 - find it below. (untested but obvious)
Ingo
-----------------------> Subject: x86: replace LOCK_PREFIX in futex.h From: Thomas Gleixner <tglx@linutronix.de>
The exception fixup for the futex macros __futex_atomic_op1/2 and futex_atomic_cmpxchg_inatomic() is missing an entry when the lock prefix is replaced by a NOP via SMP alternatives.
Chuck Ebert tracked this down from the information provided in: https://bugzilla.redhat.com/show_bug.cgi?id=429412
A possible solution would be to add another fixup after the LOCK_PREFIX, so both the LOCK and NOP case have their own entry in the exception table, but it's not really worth the trouble.
Simply replace LOCK_PREFIX with lock and keep those untouched by SMP alternatives.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> --- include/asm-x86/futex_32.h | 6 +++--- include/asm-x86/futex_64.h | 6 +++--- 2 files changed, 6 insertions(+), 6 deletions(-)
Index: linux-2.6.24/include/asm-x86/futex_32.h =================================================================== --- linux-2.6.24.orig/include/asm-x86/futex_32.h +++ linux-2.6.24/include/asm-x86/futex_32.h @@ -28,7 +28,7 @@ "1: movl %2, %0\n\ movl %0, %3\n" \ insn "\n" \ -"2: " LOCK_PREFIX "cmpxchgl %3, %2\n\ +"2: lock; cmpxchgl %3, %2\n \ jnz 1b\n\ 3: .section .fixup,\"ax\"\n\ 4: mov %5, %1\n\ @@ -68,7 +68,7 @@ futex_atomic_op_inuser (int encoded_op, #endif switch (op) { case FUTEX_OP_ADD: - __futex_atomic_op1(LOCK_PREFIX "xaddl %0, %2", ret, + __futex_atomic_op1("lock; xaddl %0, %2", ret, oldval, oldval, uaddr, oparg); break; case FUTEX_OP_OR: @@ -111,8 +111,8 @@ futex_atomic_cmpxchg_inatomic(int __user return -EFAULT; __asm__ __volatile__( - "1: " LOCK_PREFIX "cmpxchgl %3, %1 \n" + "1: lock; cmpxchgl %3, %1 \n" "2: .section .fixup, \"ax\" \n" "3: mov %2, %0 \n" " jmp 2b \n" Index: linux-2.6.24/include/asm-x86/futex_64.h =================================================================== --- linux-2.6.24.orig/include/asm-x86/futex_64.h +++ linux-2.6.24/include/asm-x86/futex_64.h @@ -27,7 +27,7 @@ "1: movl %2, %0\n\ movl %0, %3\n" \ insn "\n" \ -"2: " LOCK_PREFIX "cmpxchgl %3, %2\n\ +"2: lock; cmpxchgl %3, %2\n \ jnz 1b\n\ 3: .section .fixup,\"ax\"\n\ 4: mov %5, %1\n\ @@ -62,7 +62,7 @@ futex_atomic_op_inuser (int encoded_op, __futex_atomic_op1("xchgl %0, %2", ret, oldval, uaddr, oparg); break; case FUTEX_OP_ADD: - __futex_atomic_op1(LOCK_PREFIX "xaddl %0, %2", ret, oldval, + __futex_atomic_op1("lock; xaddl %0, %2", ret, oldval, uaddr, oparg); break; case FUTEX_OP_OR: @@ -101,8 +101,8 @@ futex_atomic_cmpxchg_inatomic(int __user return -EFAULT; __asm__ __volatile__( - "1: " LOCK_PREFIX "cmpxchgl %3, %1 \n" + "1: lock; cmpxchgl %3, %1 \n" "2: .section .fixup, \"ax\" \n" "3: mov %2, %0 \n" " jmp 2b \n"
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