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SubjectRe: Question about kmsg_dump for OOPS
Hi Jin!

On Thu, 03 Dec 2009 12:04:46 +0900
Jin Dongming <jin.dongming@np.css.fujitsu.com> wrote:

> I have a question about kmsg_dump which needs your help.
> The question is as following:
> Why not put the kmsg_dump() for OOPS into oops_end() and before the branch
> of crash_kexec()?
>
> The reason for the question is as following:
> Now the kmsg_dump() for OOPS is added in oops_exit(). When OOPS happened,
> kernel will call oops_end(). If the crash_kexec() is executed first in
> oops_end(), the oops_exit() could not be called. And also the kmsg_dump()
> for PANIC could not be executed. So I think that the kmsg_dump() for OOPS
> will lose its real meaning.

It would be OK to move it for my part, I understand your reasoning.
How this is handled seems to vary a bit between architectures though.
ARM has (arch/arm/kernel/die.c)

NORET_TYPE void die(const char *str, struct pt_regs *regs, int err)
{
[...]
if (panic_on_oops)
panic("Fatal exception");

oops_exit();
[...]

while x86 does (arch/x86/kernel/dumpstack.c):

void __kprobes oops_end(unsigned long flags, struct pt_regs *regs, int signr)
{
if (regs && kexec_should_crash(current))
crash_kexec(regs);
[...]
oops_exit();
[...]
if (in_interrupt())
panic("Fatal exception in interrupt");
if (panic_on_oops)
panic("Fatal exception");


There was some additional discussion on this a while ago in these two
threads:

http://lkml.org/lkml/2009/11/11/404

http://lkml.org/lkml/2009/10/23/131

where there additionally was a request to move

atomic_notifier_call_chain(&panic_notifier_list, 0, buf);

before kmsg_dump() and crash_kexec(). I can't immediately see any
problem with this approach, but I'm no expert on kexec. The discussion
didn't really conclude on this matter though.

// Simon


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