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SubjectRe: [PATCH] 2.5.21 IDE 91
On Fri, Jun 14 2002, Linus Torvalds wrote:
>
>
> On Fri, 14 Jun 2002, Jens Axboe wrote:
> >
> > - current 2.5 bk deadlocks reading partition info off disk. Again a
> > locking problem I suppose, to be honest I just got very tired when
> > seeing it happen and didn't want to spend tim looking into it.
>
> Hmm. There's a bug in "balance_irq()" if you are trying to run a SMP
> kernel on an UP machine right now, and it _might_ be that the lockup has
> nothing to do with the IDE layer, but simple with the first PCI interrupt
> (as opposed to local timer interrupt) coming in.
>
> One-liner from Zwane Mwaikambo (cut-and-paste, so space is wrong, please
> apply by hand).
>
> --- linux-2.5.19/arch/i386/kernel/io_apic.c.orig Fri Jun 14 17:43:20 2002
> +++ linux-2.5.19/arch/i386/kernel/io_apic.c Fri Jun 14 17:42:23 2002
> @@ -251,7 +251,7 @@
> irq_balance_t *entry = irq_balance + irq;
> unsigned long now = jiffies;
>
> - if (unlikely(entry->timestamp != now)) {
> + if ((entry->timestamp != now) && (smp_num_cpus > 1)) {
> unsigned long allowed_mask;
> int random_number;
>
> I don't know. Might be the IDE code too, of course.

If it's just a SMP kernel on UP, then that's not the problem here. This
was SMP kernel on SMP machine.

--
Jens Axboe

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