[PATCH -v2 6/8] kexec jump: fix for lockdep

[PATCH -v2 6/8] kexec jump: fix for lockdep

[Huang Ying]

Replace local_irq_disable() with raw_local_irq_disable() to prevent
lockdep complain.

Signed-off-by: Huang Ying <ying.huang@intel.com>

---
 arch/x86/kernel/machine_kexec_32.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/machine_kexec_32.c
+++ b/arch/x86/kernel/machine_kexec_32.c
@@ -123,7 +123,7 @@ void machine_kexec(struct kimage *image)
 	tracer_disable();
 
 	/* Interrupts aren't acceptable while we reboot */
-	local_irq_disable();
+	raw_local_irq_disable();
 
 	if (image->preserve_context) {
 #ifdef CONFIG_X86_IO_APIC

Re: [PATCH -v2 6/8] kexec jump: fix for lockdep

[Peter Zijlstra]

On Fri, 2008-08-08 at 14:52 +0800, Huang Ying wrote:
> Replace local_irq_disable() with raw_local_irq_disable() to prevent
> lockdep complain.


Uhhm, please provide more information - just using raw_* to silence
lockdep is generally the wrong thing to do.

> Signed-off-by: Huang Ying <ying.huang@intel.com>
> 
> ---
>  arch/x86/kernel/machine_kexec_32.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/kernel/machine_kexec_32.c
> +++ b/arch/x86/kernel/machine_kexec_32.c
> @@ -123,7 +123,7 @@ void machine_kexec(struct kimage *image)
>  	tracer_disable();
>  
>  	/* Interrupts aren't acceptable while we reboot */
> -	local_irq_disable();
> +	raw_local_irq_disable();
>  
>  	if (image->preserve_context) {
>  #ifdef CONFIG_X86_IO_APIC
> 
> 
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Re: [PATCH -v2 6/8] kexec jump: fix for lockdep

[Huang Ying]

On Fri, 2008-08-08 at 12:13 +0200, Peter Zijlstra wrote:
> On Fri, 2008-08-08 at 14:52 +0800, Huang Ying wrote:
> > Replace local_irq_disable() with raw_local_irq_disable() to prevent
> > lockdep complain.
> Uhhm, please provide more information - just using raw_* to silence
> lockdep is generally the wrong thing to do.

In traditional kexec, the new kernel will replace current one, so the
irq is simply disabled. But now jumping back from kexeced kernel is
supported, so the irq should be enabled again.

The code sequence of irq during kexec jump is as follow:

local_irq_disable(); /* in kernel_kexec() */
local_irq_disable(); /* in machine_kexec() */
local_irq_enable(); /* in kernel_kexec() */

The disable and enable is not match. Maybe another method is to use
local_irq_save(), local_irq_restore() pair in machine_kexec(), so the
disable and enable is matched.

Best Regrards,
Huang Ying

Re: [PATCH -v2 6/8] kexec jump: fix for lockdep

[Peter Zijlstra]

On Mon, 2008-08-11 at 08:59 +0800, Huang Ying wrote:
> On Fri, 2008-08-08 at 12:13 +0200, Peter Zijlstra wrote:
> > On Fri, 2008-08-08 at 14:52 +0800, Huang Ying wrote:
> > > Replace local_irq_disable() with raw_local_irq_disable() to prevent
> > > lockdep complain.
> > Uhhm, please provide more information - just using raw_* to silence
> > lockdep is generally the wrong thing to do.
> 
> In traditional kexec, the new kernel will replace current one, so the
> irq is simply disabled. But now jumping back from kexeced kernel is
> supported, so the irq should be enabled again.
> 
> The code sequence of irq during kexec jump is as follow:
> 
> local_irq_disable(); /* in kernel_kexec() */
> local_irq_disable(); /* in machine_kexec() */
> local_irq_enable(); /* in kernel_kexec() */
> 
> The disable and enable is not match. Maybe another method is to use
> local_irq_save(), local_irq_restore() pair in machine_kexec(), so the
> disable and enable is matched.

And its the machine kernel's lockdep instance that goes complain?

whichever annotation gets used - and I think I can agree that raw_*
might be approriate there, this should be accompanied with a rather
elaborate changelog and preferably a comment in the code too. Without
such we'll be wondering in the years to come WTH happens here.

Re: [PATCH -v2 6/8] kexec jump: fix for lockdep

[Huang Ying]

On Mon, 2008-08-11 at 08:09 +0200, Peter Zijlstra wrote:
> On Mon, 2008-08-11 at 08:59 +0800, Huang Ying wrote:
> > On Fri, 2008-08-08 at 12:13 +0200, Peter Zijlstra wrote:
> > > On Fri, 2008-08-08 at 14:52 +0800, Huang Ying wrote:
> > > > Replace local_irq_disable() with raw_local_irq_disable() to prevent
> > > > lockdep complain.
> > > Uhhm, please provide more information - just using raw_* to silence
> > > lockdep is generally the wrong thing to do.
> > 
> > In traditional kexec, the new kernel will replace current one, so the
> > irq is simply disabled. But now jumping back from kexeced kernel is
> > supported, so the irq should be enabled again.
> > 
> > The code sequence of irq during kexec jump is as follow:
> > 
> > local_irq_disable(); /* in kernel_kexec() */
> > local_irq_disable(); /* in machine_kexec() */
> > local_irq_enable(); /* in kernel_kexec() */
> > 
> > The disable and enable is not match. Maybe another method is to use
> > local_irq_save(), local_irq_restore() pair in machine_kexec(), so the
> > disable and enable is matched.
> 
> And its the machine kernel's lockdep instance that goes complain?
> 
> whichever annotation gets used - and I think I can agree that raw_*
> might be approriate there, this should be accompanied with a rather
> elaborate changelog and preferably a comment in the code too. Without
> such we'll be wondering in the years to come WTH happens here.

Sorry, I find there is no complain from lockdep. Un-paired irq
disable/enable has no problem with lockdep, just increase something such
as "redundant_hardirqs_off". Please ignore this thread.

Best Regards,
Huang Ying