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SubjectRe: [PATCH x86/nmi 2/2] x86/nmi: Print reasons why backtrace NMIs are ignored
On Thu, Jan 05, 2023 at 11:40:30AM +0100, Ingo Molnar wrote:
>
> * Paul E. McKenney <paulmck@kernel.org> wrote:
>
> > +#ifdef CONFIG_NMI_CHECK_CPU
> > +
> > +static char *nmi_check_stall_msg[] = {
> > +/* */
> > +/* +--------- nsp->idt_seq_snap & 0x1: CPU is in NMI handler. */
> > +/* | +------ cpu_is_offline(cpu) */
> > +/* | | +--- nsp->idt_calls_snap != atomic_long_read(&nsp->idt_calls): */
> > +/* | | | NMI handler has been invoked. */
> > +/* | | | */
> > +/* V V V */
> > +/* 0 0 0 */ "NMIs are not reaching exc_nmi handler",
> > +/* 0 0 1 */ "exc_nmi handler is ignoring NMIs",
> > +/* 0 1 0 */ "CPU is offline and NMIs are not reaching exc_nmi handler",
> > +/* 0 1 1 */ "CPU is offline and exc_nmi handler is legitimately ignoring NMIs",
> > +/* 1 0 0 */ "CPU is in exc_nmi handler and no further NMIs are reaching handler",
> > +/* 1 0 1 */ "CPU is in exc_nmi handler which is legitimately ignoring NMIs",
> > +/* 1 1 0 */ "CPU is offline in exc_nmi handler and no further NMIs are reaching exc_nmi handler",
> > +/* 1 1 1 */ "CPU is offline in exc_nmi handler which is legitimately ignoring NMIs",
>
> That kind of disambiguation of why a CPU is stuck looks really useful:
>
> Reviewed-by: Ingo Molnar <mingo@kernel.org>

Glad you like it and thank you! I will apply this on the next rebase.

> One small suggestion would be to do this in the messages:
>
> s/exc_nmi handler
> /exc_nmi() handler
>
> ... to make it clear that it's a regular kernel function [well, hw entry
> handler], not a function pointer or some other indirection? No strong
> feelings though.

Will do! I would balk at "DEFINE_IDTENTRY_RAW(exc_nmi)", though. ;-)

Thanx, Paul

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