linux-kernel - Re: [PATCH -rt 2/9] Dont allow non-threaded softirqs and threaded hardirqs

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Message-ID: <Pine.LNX.4.58.0707300724120.8151@gandalf.stny.rr.com>
Date:	Mon, 30 Jul 2007 07:28:42 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Daniel Walker <dwalker@...sta.com>, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: Re: [PATCH -rt 2/9] Dont allow non-threaded softirqs and threaded
 hardirqs

--
On Mon, 30 Jul 2007, Ingo Molnar wrote:
> > From: Steven Rostedt <rostedt@...dmis.org>
> >
> > I think this was sent before, and it did cause problems before. Would
> > there be *any* reason to have non-threaded softirqs but threaded
> > hardirqs. I can see lots of issues with that.
>
> please elaborate in precise terms: what issues can you see?
>

Hi Ingo,

I don't remember the exact details, I can try to find the thread. But I
remember someone was having their system lock up strangly. We later found
that they had softirqs as normal softirqs and interrupts as threads.  I
think there was some driver that didn't expect the softirq to preempt the
irq handler.  Perhaps the softirq was using spin_lock_irq while the irq
thread was just using spin_lock, which I can see as being something
normal.

The standard Linux does not expect an interrupt to be preempted by a
softirq, and with interrupts as threads but not softirqs, I can see that
happening a lot.

-- Steve

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