linux-kernel - Re: real time hang w/ latency tracing

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Date:	Wed, 4 Apr 2007 17:42:49 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: real time hang w/ latency tracing


* Daniel Walker <dwalker@...sta.com> wrote:

> > >  struct uart_port {
> > > +#ifdef CONFIG_LATENCY_TIMING
> > > +	raw_spinlock_t		lock;			/* port lock */
> > > +#else
> > >  	spinlock_t		lock;			/* port lock */
> > > +#endif
> > 
> > ugh - this will only cause other problems if anyone else is trying 
> > to use the serial code. This needs a cleaner fix - such as not doing 
> > that printk from atomic context.
> 
> I assumed this fix wasn't totally right .. Interrupts could be enabled 
> just before printing , after any critical stuff has happened then 
> disabled again after printing .. Or are you thinking of something more 
> complex?

i mean non-printk related breakages to the normal serial driver - which 
is now surprised by this raw lock in an -rt kernel.

this is a hard issue and there's no easy solution i can see. neither 
having it as a raw lock is a good solution, nor having it as a 
preemptible lock is a good solution.

	Ingo
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