Re: [PATCH] lockup_detector: Make DETECT_HUNT_TASK default depend on LOCKUP_DETECTOR

[Ingo Molnar <mingo@elte.hu>]

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> > The thing is, CONFIG_DETECT_SOFTLOCKUP was default-y before, so many 
> > people had it enabled [and had it forced-enabled if DEBUG_KERNEL was off], 
> > even if they didnt really want or need it.
> 
> Hmm. It was:
> 
> config DETECT_SOFTLOCKUP
> 	bool "Detect Soft Lockups"
> 	depends on DEBUG_KERNEL && !S390
> 	default y
> 
> It means it's default enabled only if DEBUG_KERNEL, right? Then if you don't 
> select CONFIG_DEBUG_KERNEL, it's fine as it won't be selected.

Indeed, you are right.

Anyway, i think the general point remains: i'm not sure we should 
default-enable this feature.

> But I agree with you. There is a bunch of config options for which selection 
> is a duty when you are a kernel developer: PROVE_LOCKING, DETECT_HUNG_TASK, 
> DEBUG_PREEMPT, PROVE_RCU, etc... Because they all show (or prove we can 
> have) bugs that one might miss without these options. Softlockups are rarely 
> part of them because even without the lockup detector enabled, you'll 
> observe something is wrong.

Note that it's now detecting all kinds of lockups: softlockups, hard lockups 
and even unkillable hung tasks.

	Ingo