Re: [debug patch] printk: Add a printk killswitch to robustify NMIwatchdog messages

[Peter Zijlstra]

On Mon, 2011-06-06 at 18:08 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > On Mon, 2011-06-06 at 17:52 +0200, Ingo Molnar wrote:
> > > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > > 
> > > > Needs more staring at, preferably by someone who actually 
> > > > understands that horrid mess :/ Also, this all still doesn't make 
> > > > printk() work reliably while holding rq->lock.
> > > 
> > > So, what about my suggestion to just *remove* the wakeup from there 
> > > and use the deferred wakeup mechanism that klogd uses.
> > > 
> > > That would make printk() *visibly* more robust in practice.
> > 
> > That's currently done from the jiffy tick, do you want to effectively
> > delay releasing the console_sem for the better part of a jiffy?
> 
> Yes, and we already do it in some other circumstances. 

We do?

> Can you see 
> any problem with that? klogd is an utter slowpath anyway.

but console_sem isn't klogd. We delay klogd and that's perfectly fine,
but afaict we don't delay console_sem.
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