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SubjectRe: [PATCH 26/28] kdb,panic,debug_core: Allow the debug core to receive a panic before smp_send_stop()
Andrew Morton <akpm@linux-foundation.org> writes:

> On Fri, 12 Feb 2010 17:43:39 -0600 Jason Wessel <jason.wessel@windriver.com> wrote:
>
>> >> printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf);
>> >> #ifdef CONFIG_DEBUG_BUGVERBOSE
>> >> dump_stack();
>> >> @@ -91,8 +94,6 @@ NORET_TYPE void panic(const char * fmt, ...)
>> >> */
>> >> smp_send_stop();
>> >>
>> >> - atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
>> >> -
>> >> bust_spinlocks(0);
>> >>
>> >> if (!panic_blink)
>> >>
>> >
>> > So the notifier call now happens before all the printks and the kexec
>> > and kmsg_dump handling. What effect does this have upon the code which
>> > implements kexec and kmsg_dump?
>> >
>> >
>>
>> I certainly don't want to break kexec or alter any behavior, does that
>> mean kgdb / kdb should hook the kexec for notification?
>>
>> I think ideally it is a end user's preference as to if they want in via
>> kexec or the kernel debugger. Calling the smp_send_stop() prior to the
>> notifier was a death sentence for the kernel debugger.
>>
>> Perhaps I can move the notifier before smp_send_stop()?
>
> Well. My question can be simplified to "does this break existing code"?

Yes. Removing the bust_spinlocks(1) and moving the panic notification up
will measurably decrease the reliability of crash dump capture. I expect
it will even result in dead_locks where we fail to print the panic message
for people who are trying to debug via the console.

Eric


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