Re: 2.6.33.6-rt26: consoles not working properly
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On Tue, 2010-07-27 at 11:41 +0200, Thomas Gleixner wrote:
> On Sun, 25 Jul 2010, Mike Galbraith wrote:
>
> > On Fri, 2010-07-23 at 16:39 +0200, Mike Galbraith wrote:
> > > Greetings,
> > >
> > > Consoles (serial and vt) are going silent after.
> > >
> > > [ 1.100178] Freeing initrd memory: 9348k freed
> > > [ 1.453009] Freeing unused kernel memory: 1000k freed
> > > [ 1.464463] Freeing unused kernel memory: 512k freed
> > > [ 1.469724] Freeing unused kernel memory: 360k freed
> > >
> > > If the kernel is configured PREEMPT_VOLUNTARY, consoles work fine again.
> > > So far, I've only eyeballed the rt patch, and noticed nothing. I'll be
> > > poking around in (shudder) console code soon I suppose, but before I
> > > start that.. adventure, is this a known issue?
> >
> > Hm, that was suspiciously easy.
> >
> > console: really enable interrupts in release_console_mutex()
> >
> > vprintk()
> > raw_local_irq_save()
> > acquire_console_mutex_for_printk()
> > release_console_mutex()
> > raw_spin_unlock_save()
> > raw_spin_unlock_irqrestore()
> > call_console_drivers()
> > _call_console_drivers()
> > __call_console_drivers()
> > console_atomic_safe() "nope".
> >
> > Signed-off-by: Mike Galbraith <efault@xxxxxx>
> >
> > ---
> > kernel/printk.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > Index: tip-rt/kernel/printk.c
> > ===================================================================
> > --- tip-rt.orig/kernel/printk.c
> > +++ tip-rt/kernel/printk.c
> > @@ -1072,7 +1072,7 @@ void release_console_mutex(void)
> > * with interrupts disabled):
> > */
> > #ifdef CONFIG_PREEMPT_RT
> > - raw_spin_unlock_irqrestore(&logbuf_lock, flags);
> > + raw_spin_unlock_irq(&logbuf_lock);
>
> Not really a good idea. If printk is called from an irq disabled
> region, then we unconditionally enabled interrupts here. The comment
> above this is misleading and needs to be removed. We had problems in
> that area before. Does the following patch solve your problem as well ?
Aha. Yes, it does.
-Mike
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