Re: lockdep warning in check_flags()

[Ingo Molnar <mingo@elte.hu>]

* 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";	\