Vivek Goyal <[email protected]> writes:
> On Mon, Mar 06, 2006 at 10:43:32PM +0100, Andi Kleen wrote:
>> On Mon, Mar 06, 2006 at 11:40:34AM -0500, Vivek Goyal wrote:
>> >
>> > o check_timer() routine fails while second kernel is booting after a crash
>> > on an opetron box. Problem happens because timer vector (0x31) seems to be
>> > locked.
>> >
>> > o After a system crash, it is not safe to service interrupts any more, hence
>> > interrupts are disabled. This leads to pending interrupts at LAPIC. LAPIC
>> > sends these interrupts to the CPU during early boot of second kernel. Other
>> > pending interrupts are discarded saying unexpected trap but timer interrupt
>> > is serviced and CPU does not issue an LAPIC EOI because it think this
>> > interrupt came from i8259 and sends ack to 8259. This leads to vector 0x31
>> > locking as LAPIC does not clear respective ISR and keeps on waiting for
>> > EOI.
>> >
>> > o In this patch, one extra EOI is being issued in check_timer() to unlock
> the
>> > vector. Please suggest if there is a better way to handle this situation.
>>
>> Shouldn't we rather do this for all interrupts when the APIC is set up?
>> I don't see how the timer is special here.
>>
>
> Timer is a special case here.
>
> In other cases, the moment interrupts are enabled on cpu, LAPIC pushes pending
> interrupts to cpu and it is ignored as bad irq using ack_bad_irq(). This
> still sends EOI to LAPIC if LPAIC support is compiled in.
>
> But for timer, the moment pending interrupt is pushed to cpu, it is handled
> as valid interrupt and cpu assumes that it came from 8259 and sends ack to
> 8259 and not to LAPIC. Hence leads to missing EOI for timer vector and
> deadlock.
>
> But still doing it generic manner for all interrupts while setting up LAPIC
> probably makes more sense. Please find attached the patch.
A couple of questions.
Does this need to be in #ifdef CONFIG_CRASS_DUMP?
If this code is truly safe I expect we could run it on every bootup
simply to be more robust.
Why is APIC_ISR_NR a hard code? I think there is an apic register
that tells the count.
Does ack_APIC_irq take an argument? I am confused that we are calling
ack_APIC_irq() potentially 8*32 times without passing it anything.
Eric
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