linux-kernel - Re: [2.6.23-rt3] NMI watchdog trace of deadlock

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Message-ID: <Pine.LNX.4.58.0710270915460.6459@gandalf.stny.rr.com>
Date:	Sat, 27 Oct 2007 09:22:30 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jaswinder Singh <jaswinderlinux@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, Nick Piggin <nickpiggin@...oo.com.au>,
	Mike Galbraith <efault@....de>,
	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [2.6.23-rt3] NMI watchdog trace of deadlock


--

On Sat, 27 Oct 2007, Jaswinder Singh wrote:

> Hello Ingo,
>
> On 10/27/07, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > it's not atomic interrupt context but irq thread context - and -rt
> > remaps kmap_atomic() to kmap() internally.
> >
> > the problem seems to be what Mike's patch works around: fiddling with
> > irq flags in the ntfs code. That fiddling seems quite unnecessary at
> > first sight.
> >
>
> Is this a nice idea to go inside device drivers and filesystem and
> make changes in kernel source code to enable RT.

Actually the question is, is it a nice idea for drivers to disable
interrupts for no obvious reason. I'm sure you have a reason, but it's not
obvious to me why. What does it protect? Is it SMP safe?

When tuning a RT system for the customer, the first thing we recommend is
to check to make sure all the drivers in use do not disable interrupts.

>
> RT related change should be in header files, so that we don't need to
> make changes for drivers or filesystem source files.
>
> And when user will disable RT then these patches will again make problems.
>
> We need to find some better alternative.

We do have the local_irq_save_nort that Mike has posted.  This is a simple
wrapper around local_irq_save that enables it when RT is not configured,
and is a nop when RT is configured.

Thanks,

-- Steve

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