lkml.org 
[lkml]   [2009]   [Jul]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] sysrq, kdump: fix regression, revert "simplify sysrq-c handler"
On Wed, Jul 22, 2009 at 11:01:29AM +0900, Hidetoshi Seto wrote:
> Neil Horman wrote:
> > None of this answers Erics question, what is it that you could do before, that
> > you couldn't do now?
>
> One is, as Ohmichi-san pointed, triggering kdump via echo c > /proc/sysrq-trigger.
>
> In contrast to oops via SysRq-c from keyboard interrupt which results in
> panic due to in_interrupt(), oops via echo-c will not become panic unless
> panic_on_oops.
>
> So in other words, we could expect same effect in both of echo-c and SysRq-c
> before, but now we cannot because it depends on the panic_on_oops.
> Isn't it a regression?
>
Only if you blindly consider a change in behavior to be a regression. consider
that previously executing a sysrq-c did the same thing if you did a echo c >
/proc/sysrq-trigger on a keyboard sysrq-c, but did different things based on
weather or not your had a kexec kernel loaded.

> Whether kdump should be executed on oops (which is not panic) or not is a
> separate thing.
>
> > There are reasons to want to have a convenient way to
> > crash the kernel, other than to test kdump (several distributions have augmented
> > sysrq-c to do this for some time to test other previous dump mechanisms and
> > features), so while its not been upstream, saying that its well known to test
> > kdump without causing an oops is a bit of a misleading statement.
>
> Let make me sure the difference between 'crash', 'oops', and 'panic'.
> At least 'oops' is not panic, as is obvious from the name of panic_on_oops.
> And it seems you are using 'crash' and 'oops' in mixture.
>
I'm perfectly well aware of the difference, I just assert theres value to having
sysrq-c be able to test both paths, especially given that we already have the
sysrq-c sysctl available to toggle behavior for just this case.

> If you mean 'crash' as 'panic', my complaint is echo-c does not panic while
> SysRq-c does panic. So if possible I'd like to suggest a change like:
>
See above, I think theres value to having sysrq-c be able to do both, although I
agree the method by which it triggers both is a bit muddled.

> static void sysrq_handle_crash(int key, struct tty_struct *tty)
> {
> - char *killer = NULL;
> - *killer = 1;
> + panic("SysRq-triggered panic!\n");
> }
>
Well, this removes the ability from sysrq-c to test the oops handling path, but
I suppose it does buy us consistent behavior between the keyboard and proc
interfaces, which is likely more important. I can agree to that. Perhaps we
can create another sysctl to test the oops path later.

> I agree that causing a real crash(panic) is better way to test crashdump than
> calling the entry function of the crashdump directly, and also that opening
> the path for other dump mechanisms is welcomed.
>
Ok, so we're in line there :)

> > It seems to
> > me that right now your major complaint is that the documentation is out of date,
> > and you're having to do things slightly differently to get the same behavioral
> > results. Would it solve your issue, if we simply updated the documentation to
> > illustrate how it works now?
>
> Of course the documentation should be updated asap.
> But I think the major complaint is about a difference in the behaviors of SysRq-c
> and "echo c > /proc/sysrq-trigger".
>
Ok, I can agree with that. I'd support a change like what you have above to
bring the keyboard and proc interface behavior in line.

Regards
Neil


>
> Thanks,
> H.Seto
>
>


\
 
 \ /
  Last update: 2009-07-22 13:13    [W:0.095 / U:4.520 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site