linux-kernel - Re: [RFC PATCH] x86/apic: Fix BUG due to multiple allocation of legacy vectors.

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Date:   Thu, 20 May 2021 10:17:39 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Imran Khan <imran.f.khan@...cle.com>, mingo@...hat.com,
        bp@...en8.de
Cc:     x86@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [RFC PATCH] x86/apic: Fix BUG due to multiple allocation of legacy vectors.

Imran,

On Wed, May 19 2021 at 23:39, Imran Khan wrote:
> During activation of secondary CPUs, lapic_online is
> invoked to initialize vectors. While lapic_online
> installs legacy vectors on all CPUs, it does not set
> the corresponding bits in per CPU bitmap maintained
> under irq_matrix.
> This may result in these legacy vectors getting allocated
> by irq_matrix_alloc and if that happens subsequent invocation
> of apic_update_vector will cause BUG like the one shown below:
>
> [  154.738226] kernel BUG at arch/x86/kernel/apic/vector.c:172!

please trim the backtrace. It's not really relevant for understanding
the problem.

> This patch marks these legacy vectors as assigned in irq_matrix

git grep 'This patch' Documentation/process/

> so that corresponding bits in percpu bitmaps get set and these
> legacy vectors don't get reallocted.

This is just wrong.

True legacy interrupts (PIC delivery) are marked as system vectors. See
lapic_assign_legacy_vector(). That prevents them from being allocated.

> [  154.858092] CPU: 22 PID: 3569 Comm: ifup-eth Not tainted 5.8.0-20200716.x86_64 #1

I have no idea what this 5.8.0-magic-date kernel is.

Have you verified that this problem exists with upstream?

Thanks,

        tglx