Re: [Xen-devel] [PATCH 2/2] Allow kdump with crash_kexec_post_notifiers

[Petr Tesarik <ptesarik@xxxxxxxx>]

On Mon, 1 Aug 2016 16:22:18 +0200
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> >>> On 01.08.16 at 16:15, <PTesarik@xxxxxxxx> wrote:
>[...]
> > But let me repeat: if PV kexec works, then it has always had priority
> > over the hypercall. If it doesn't work, then it has always been broken.
> > For the latter case, I agree that the kernel should not even allow to
> > load the kexec image, but that's unrelated to my patch.
> 
> It's not, afaict: without your patch, the hypercall to report the guest
> crashed would be made unconditionally, without even an attempt to
> load that secondary kernel.

That's a misunderstanding then. Without my patch and without
'crash_kexec_post_notifiers' on the kernel command line, panic() _will_
attempt kexec, see the beginning of panic():

        if (!crash_kexec_post_notifiers) {
                printk_nmi_flush_on_panic();
                __crash_kexec(NULL);
        }

That's the very first thing done, even before running the panic
handlers on panic_notifier_list.

Petr T

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