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SubjectRe: 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;

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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