Message-ID: <50F97A65.7060306@xenomai.org>
Date: Fri, 18 Jan 2013 17:37:57 +0100
From: Philippe Gerum <rpm@xenomai.org>
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Subject: Re: [Xenomai] [CRITICAL PATCH] ipipe: Re-read domain context after
	IRQ processing
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Xenomai <xenomai@xenomai.org>

On 01/18/2013 04:38 PM, Jan Kiszka wrote:
> This fixes a nasty bug on SMP boxes: We may migrate to root in the
> context of an IRQ handler, and then also to a different CPU. Therefore,
> we must not use domain contexts read before the invocation but update
> them afterward or use stable information like the domain reference.

Ack.

>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>
> We are still facing stalled, unkillable RT processes despite this fix,

Is TASK_HARDENING still lingering in task->state despite the recent 
switch_tail fix, or is this something different?

> but at least the head domain status corruption (and related warnings)
> seems to be gone now.
>
>   kernel/ipipe/core.c |    5 +++--
>   1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/ipipe/core.c b/kernel/ipipe/core.c
> index 68af0b3..6aa9572 100644
> --- a/kernel/ipipe/core.c
> +++ b/kernel/ipipe/core.c
> @@ -1173,18 +1173,19 @@ static void dispatch_irq_head(unsigned int irq) /* hw interrupts off */
>   	head->irqs[irq].handler(irq, head->irqs[irq].cookie);
>   	__ipipe_run_irqtail(irq);
>   	hard_local_irq_disable();
> +	p = ipipe_this_cpu_head_context();
>   	__clear_bit(IPIPE_STALL_FLAG, &p->status);
>
>   	/* Are we still running in the head domain? */
>   	if (likely(__ipipe_current_context == p)) {
>   		/* Did we enter this code over the head domain? */
> -		if (old == p) {
> +		if (old->domain == head) {
>   			/* Yes, do immediate synchronization. */
>   			if (__ipipe_ipending_p(p))
>   				__ipipe_sync_stage();
>   			return;
>   		}
> -		__ipipe_set_current_context(old);
> +		__ipipe_set_current_context(ipipe_this_cpu_root_context());
>   	}
>
>   	/*
>


-- 
Philippe.