[PATCH] xen/x86: set panic notifier priority to minimum

[PATCH] xen/x86: set panic notifier priority to minimum

[Radim Krčmář]

Execution is not going to continue after telling Xen about the crash.
Let other panic notifiers run by postponing the final hypercall as much
as possible.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 arch/x86/xen/enlighten.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c34bfc4..f17b292 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1339,6 +1339,7 @@ xen_panic_event(struct notifier_block *this, unsigned long event, void *ptr)
 
 static struct notifier_block xen_panic_block = {
 	.notifier_call= xen_panic_event,
+	.priority = INT_MIN
 };
 
 int xen_panic_handler_init(void)
-- 
1.9.0

Re: [PATCH] xen/x86: set panic notifier priority to minimum

[David Vrabel]

On 13/05/14 17:56, Radim Krčmář wrote:
> Execution is not going to continue after telling Xen about the crash.
> Let other panic notifiers run by postponing the final hypercall as much
> as possible.

I can't tell how important this fix is.

What notifiers does this allow to be run?  How important are they?

David

Re: [PATCH] xen/x86: set panic notifier priority to minimum

[Radim Krčmář]

2014-05-13 18:18+0100, David Vrabel:
> On 13/05/14 17:56, Radim Krčmář wrote:
> > Execution is not going to continue after telling Xen about the crash.
> > Let other panic notifiers run by postponing the final hypercall as much
> > as possible.
> 
> I can't tell how important this fix is.

Sorry, I could have put reasoning in the commit:

Not very important, depends on long linux+xen is going to last.
This patch is thinking about users/developers that would eventually find
a problem with it, and questioned our inteligence -- it makes no sense
to use the default priority for a notifier that is (can be) final.
INT_MIN is set because I don't think that Xen indended to resume domains
after crash.  (We should reason any other value as well.)

> What notifiers does this allow to be run?  How important are they?

Priority 0 (default) or lower.  Registration is stable and paravirt does
it early, so there won't be many priority 0 users before it. (None now.)

Hardware that can be passed through (most notably graphic cards), and
few debug markers (dump_kernel_offset, hung_task_panic) are affected at
the moment.

Re: [PATCH] xen/x86: set panic notifier priority to minimum

[David Vrabel]

On 13/05/14 17:56, Radim Krčmář wrote:
> Execution is not going to continue after telling Xen about the crash.
> Let other panic notifiers run by postponing the final hypercall as much
> as possible.

Applied to devel/for-linus-3.16

Thanks.

David