Re: [PATCH RFC 0/2] x86/apic: Avoid cm->allocated going negative in irq_matrix

Vitaly Kuznetsov
2021-03-11T10:19:46Z

Vitaly Kuznetsov <vkuznets@redhat.com> writes:

> I discovered that CPU0 offlining/onlining works only once:
>
> # echo 0 > /sys/devices/system/cpu/cpu0/online
> # echo 1 > /sys/devices/system/cpu/cpu0/online
> # echo 0 > /sys/devices/system/cpu/cpu0/online
> -bash: echo: write error: No space left on device
>
> with the following in dmesg:
>
> [ ... ] CPU 0 has 4294967295 vectors, 589 available. Cannot disable CPU
>
> And the problem seems to be that irq_matrix_assign()/irq_matrix_free() calls
> for PIC_CASCADE_IR are unbalanced, making cm->allocated go negative.
>
> RFC as I didn't quite get why we're making an exception for PIC_CASCADE_IR in
> the first place. Surely it is special, but for the sake of consistency we'd
> better not treat it as such. Or maybe I just misunderstood everything.
>

If the RFC part is the only thing which scares everyone off I'm ready to
drop it and pretend that I'm confident with the change)

> Vitaly Kuznetsov (2):
> x86/apic: Do not make an exception for PIC_CASCADE_IR when marking
> legacy irqs in irq_matrix
> genirq/matrix: WARN_ON_ONCE() when cm->allocated/m->total_allocated go
> negative
>
> arch/x86/kernel/apic/vector.c | 3 +--
> kernel/irq/matrix.c | 11 +++++++++--
> 2 files changed, 10 insertions(+), 4 deletions(-)

--
Vitaly