linux-kernel - Re: [PATCH 0/2] [RFC] RT: Optionally allow IRQF

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Message-Id: <1191853361.4281.5.camel@ghaskins-t60p.haskins.net>
Date:	Mon, 08 Oct 2007 10:22:41 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, mingo@...e.hu,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] [RFC] RT: Optionally allow IRQF_NODELAY on serial
	console

On Mon, 2007-10-08 at 10:10 -0400, Steven Rostedt wrote:

> This issue has hit me enough times where I've played with a few other
> ideas. I just haven't had the time to finish them. The main problem is if
> the system locks up somewhere we have a lock held that keeps us from
> scheduling. Once that happens in -rt, we are as good as dead. Since you
> can't get much info out without a JTAG or some other mechanism.
> 
> One thought I had was to create a small handler that could read the serial
> and place data into a buffer. This handler would be a IRQ_NODELAY, and it
> would wake up a serial thread to handle the data just like it would for
> normal serial output. But the serial thread would just read from the
> buffer instead of the serial itself.  In the case of a sysrq key coming
> in, the IRQ_NODELAY handler would handle it.
> 

Hi Steve,
  What you describe is exactly what I did.  The IRQF_NODELAY handler
just minimally checks to see if the character is a sysrq related one (or
KDB, if you have the KDB patches applied).  If it is not, it puts the
character into a ring-buffer and wakes a (kthread-based) tasklet to do
the normal serial/tty rx path by processing the ring.

Hope that helps to clarify.

Regards,
-Greg



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