linux-kernel - Re: IO CPU affinity test results

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Date:	Fri, 14 Mar 2008 14:05:45 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Alan D. Brunelle" <Alan.Brunelle@...com>
Cc:	linux-kernel@...r.kernel.org, npiggin@...e.de, dgc@....com
Subject: Re: IO CPU affinity test results

On Fri, Mar 14 2008, Jens Axboe wrote:
> I think that is encouraging, for such a small setup. The make results
> are particularly nice. The hangs are a bother, I have no good ideas on
> why the occur. The fact that it happens on both archs indicates that
> this is perhaps a generic problem, which is good. The code to support
> this is relatively simple, so it should be possible to go over it with a
> fine toothed comb and see if anything shows up.
> 
> You didn't get any watchdog triggers on the serial console, or anything
> like that?

Here's something that may explain it - if interrupts aren't disabled
when generic_smp_call_function_single() is called, we could deadlock
on the dst->lock. I think that the IPI invoke will have interrupt
disabled, but I'm not 100% certain.

Can you see if this passes the muster?

diff --git a/kernel/smp.c b/kernel/smp.c
index 852abd3..65808df 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -24,12 +24,13 @@ void __cpuinit generic_init_call_single_data(void)
 void generic_smp_call_function_single_interrupt(void)
 {
 	struct call_single_queue *q;
+	unsigned long flags;
 	LIST_HEAD(list);
 
 	q = &__get_cpu_var(call_single_queue);
-	spin_lock(&q->lock);
+	spin_lock_irqsave(&q->lock);
 	list_replace_init(&q->list, &list);
-	spin_unlock(&q->lock);
+	spin_unlock_irqrestore(&q->lock);
 
 	while (!list_empty(&list)) {
 		struct call_single_data *data;

-- 
Jens Axboe

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