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SubjectRe: PREEMPT_RT (2.6.33-rt17) disabled printk-to-console after console_init
On Thu, 20 May 2010, Nikita V. Youshchenko wrote:

> > > Still questions:
> > >
> > > 1) why does that prevent klogd from working?
> >
> > Patch below.
> > ...
> > @@ -1084,18 +1084,8 @@ void release_console_mutex(void)
> > #endif
> > }
> > console_locked = 0;
> > - raw_spin_unlock_irqrestore(&logbuf_lock, flags);
> > mutex_unlock(&console_mutex);
>
> Hmm... that lock is taken inside loop body, then control goes out of loop
> at 'break' statement, and then, if this line is deteled, lock is still
> held at function return. Looks wrong.

Stupid me. Yes. Drop that line.

> > > 3) I believe that 8250 serial driver is aware of preempt-rt.
> > > Could you please comment on my "2.6.33.2-rt13: RFC: fix serial
> > > console" post to linux-rt-users list
> > > (http://eeek.borgchat.net/lists/linux-rt-users/msg05569.html)
> >
> > While that can work due to the trylock, it can introduce massive
> > latencies just in case some driver reports a status change or what
> > ever.
>
> Isn't it better just manually disable console (with 'quiet' kernel command
> line option) when running in production? This may be recommended in proper
> guidelines.

No, anything which needs extra parameters for normal operation is
wrong as it affects users.

Adding a "I'm debugging, I don't care" flag for developers is the
right thing to do.

Thanks,

tglx



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