linux-kernel - Re: current_thread_info() vs task_thread

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Message-ID: <1310990097.25044.307.camel@pasglop>
Date:	Mon, 18 Jul 2011 21:54:57 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-arch@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: current_thread_info() vs task_thread_info(current)

On Mon, 2011-07-18 at 13:23 +0200, Peter Zijlstra wrote:

> So how are we going to solve this? Naively I'd think that
> current_thread_info() is short for task_thread_info(current), and thus
> the platforms for where this isn't true are broken.
> 
> I mean, what use is the thread_info not of a thread?
> 
> Comments?

Thomas just hit a bug in the platform code of said platform (powerpc
heh ?) :-)

We do it right for hard IRQs and for some reason never did it right for
softirqs.

The code is like this for the former:

static inline void handle_one_irq(unsigned int irq)
{

        .../...

	call_handle_irq(irq, desc, irqtp, desc->handle_irq);
	current->thread.ksp_limit = saved_sp_limit;
	irqtp->task = NULL;

	/* Set any flag that may have been set on the
	 * alternate stack
	 */
	if (irqtp->flags)
		set_bits(irqtp->flags, &curtp->flags);
}

So what we need, I suppose is to add those two last line to
do_softirq_onstack() as well.

Now indeed i386 needs a similar treatment on both hard and soft
irqs (along with getting rid of that stupid duplication of
call_on_stack in there, I don't think it's worth making the code
horrible like that to save one clobber and PeterZ reckons we can
probably avoid it using always_inline anyways).

I'll let you guys sort i386 out tho, I'll look at fixing ppc tomorrow :-)

Cheers,
Ben.
 

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