linux-kernel - Re: [PATCH 2/2] irq: Cleanup context state transitions in irq

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Date:	Tue, 26 Feb 2013 13:15:08 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] irq: Cleanup context state transitions in
 irq_exit()

On Fri, 22 Feb 2013, Linus Torvalds wrote:
> On Fri, Feb 22, 2013 at 7:06 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >>
> >> I prefer to let you guys have the final word on this patch. Whether you
> >> apply it or not, I fear I'll never be entirely happy either way :)
> >> That's the sad fate of dealing with circular dependencies...
> >
> > plus the butt ugly softirq semantics or the lack thereof ...
> 
> The softirq semantics are perfectly fine. Don't blame softirq for the
> fact that irq_exit() has had shit-for-brains for a long time.
> 
> Just move the whole "invoke_softirq()" thing down to *after* the
> tick_nohz_irq_exit() stuff.

We can't move tick_nohz_irq_exit() before invoke_softirq() simply
because we need to take the timers into account for NOHZ and those can
change when the softirq code runs.

So no, we need an extra check after invoke_softirq() and the same is
true for RCU.

Thanks,

	tglx


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