Re: lockdep warning in check_flags()

Ingo Molnar
2006-09-12T17:03:25Z

* Frederik Deweerdt <deweerdt@free.fr> wrote:

> On Mon, Sep 11, 2006 at 07:43:35AM +0200, Ingo Molnar wrote:
> >
> > * Frederik Deweerdt <deweerdt@free.fr> wrote:
> >
> > > Lockdep issues the following warning:
> > >
> > > [ 16.835268] Freeing unused kernel memory: 260k freed
> > > [ 16.842715] Write protecting the kernel read-only data: 432k
> > > [ 17.796518] BUG: warning at kernel/lockdep.c:2359/check_flags()
> >
> > this warning means that the "soft" and "hard" hardirqs-disabled state
> > got out of sync: the irqtrace tracking code thinks that hardirqs are
> > disabled, while in reality they are enabled. The thing to watch for are
> > new "stii" instructions in entry.S (and other assembly code), without a
> > matching TRACE_HARDIRQS_ON call. [Another, rarer possiblity is NMI code
> > saving/restoring interrupts - do you have NMIs enabled? (are there any
> > NMI counts in /proc/interrupts?)]
> NMIs were disabled. But I've just booted -mm2 and the warning went away.
> Could this be related to the recent pda changes?

yeah, it could be related to the fix below. Can you confirm that by
applying this to your -mm1 tree the message goes away?

Ingo

--------------->
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.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

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

Index: linux/arch/i386/kernel/entry.S
===================================================================
--- linux.orig/arch/i386/kernel/entry.S
+++ linux/arch/i386/kernel/entry.S
@@ -326,11 +326,12 @@ sysenter_past_esp:
testw $_TIF_ALLWORK_MASK, %cx
jne syscall_exit_work
/* if something modifies registers it must also disable sysexit */
-1: mov PT_GS(%esp), %gs
+1:
+ TRACE_IRQS_ON
+ mov PT_GS(%esp), %gs
movl PT_EIP(%esp), %edx
movl PT_OLDESP(%esp), %ecx
xorl %ebp,%ebp
- TRACE_IRQS_ON
ENABLE_INTERRUPTS_SYSEXIT
CFI_ENDPROC
.pushsection .fixup,"ax"; \