Messages in this thread | | | Date | Wed, 22 Jul 2009 09:42:11 -0400 | From | Vivek Goyal <> | Subject | Re: [PATCH] sysrq, kdump: fix regression, revert "simplify sysrq-c handler" |
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On Wed, Jul 22, 2009 at 07:10:49AM -0400, Neil Horman wrote: > 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. >
Can't we just set panic_on_oops = 1 in sysrq_handle_crash()? This will make sure that we test oops path as well as have consistent behavior between two methods of sysrc-c invocation.
Thanks Vivek
> > 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 > > > >
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