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

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Message-ID: <87ft129enb.fsf@vitty.brq.redhat.com>
Date:   Thu, 11 Mar 2021 11:19:04 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 0/2] x86/apic: Avoid cm->allocated going negative in
 irq_matrix

Vitaly Kuznetsov <vkuznets@...hat.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