Re: [patch] i386-PDA, lockdep: fix %gs restore

Jeremy Fitzhardinge
2006-09-11T21:37:27Z

Andi Kleen wrote:
> On Monday 11 September 2006 07:25, Ingo Molnar wrote:
>
>> Jeremy,
>>
>> could you back out Andi's patch and try the patch below, does it fix the
>> crash too?
>>
>
> I folded it into the original patch now thanks
>

Ingo's patch was wrong. Here's an update:

Subject: [patch] i386-PDA, lockdep: fix %gs restore
From: Ingo Molnar <mingo@elte.hu>

in the syscall exit path the %gs selector has to be restored _after_ the
last kernel function has been called. If lockdep is enabled then this
kernel function is TRACE_IRQS_ON.

[ Make sure the move to %gs retains its exception label - jeremy@xensource.com ]

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>

---
arch/i386/kernel/entry.S | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff -r cead1b87fd17 arch/i386/kernel/entry.S
--- a/arch/i386/kernel/entry.S Sun Sep 10 16:28:43 2006 -0700
+++ b/arch/i386/kernel/entry.S Mon Sep 11 14:22:36 2006 -0700
@@ -326,11 +326,11 @@ 1: movl (%ebp),%ebp
testw $_TIF_ALLWORK_MASK, %cx
jne syscall_exit_work
/* if something modifies registers it must also disable sysexit */
-1: mov PT_GS(%esp), %gs
movl PT_EIP(%esp), %edx
movl PT_OLDESP(%esp), %ecx
+ TRACE_IRQS_ON
+1: mov PT_GS(%esp), %gs
xorl %ebp,%ebp
- TRACE_IRQS_ON
ENABLE_INTERRUPTS_SYSEXIT
CFI_ENDPROC
.pushsection .fixup,"ax"; \