linux-kernel - Re: [PATCH v3 3/3] PCI: dwc: Enable MSI affinity support

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Message-ID: <87sebsdcte.ffs@tglx>
Date: Mon, 26 Jan 2026 08:59:25 +0100
From: Thomas Gleixner <tglx@...nel.org>
To: Radu Rendec <rrendec@...hat.com>, Jon Hunter <jonathanh@...dia.com>,
 Manivannan Sadhasivam <mani@...nel.org>
Cc: Daniel Tsai <danielsftsai@...gle.com>, Marek Behún
 <kabel@...nel.org>,
 Krishna Chaitanya Chundru <quic_krichai@...cinc.com>, Bjorn Helgaas
 <bhelgaas@...gle.com>, Rob Herring <robh@...nel.org>, Krzysztof
 Wilczyński
 <kwilczynski@...nel.org>, Lorenzo
 Pieralisi <lpieralisi@...nel.org>, Jingoo Han <jingoohan1@...il.com>, Brian
 Masney <bmasney@...hat.com>, Eric Chanudet <echanude@...hat.com>,
 Alessandro Carminati <acarmina@...hat.com>, Jared Kangas
 <jkangas@...hat.com>, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org, "linux-tegra@...r.kernel.org"
 <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] PCI: dwc: Enable MSI affinity support

On Thu, Jan 22 2026 at 18:31, Radu Rendec wrote:
> The CPUs are taken offline one by one, starting with CPU 7. The code in
> question runs on the dying CPU, and with hardware interrupts disabled
> on all CPUs. The (simplified) call stack looks like this:
>
> irq_migrate_all_off_this_cpu
>   for_each_active_irq
>     migrate_one_irq
>       irq_do_set_affinity
>         irq_chip_redirect_set_affinity (via chip->irq_set_affinity)
>
> The debug patch I gave you adds:
>  * a printk to irq_chip_redirect_set_affinity (which is very small)
>  * a printk at the beginning of migrate_one_irq
>
> Also, the call to irq_do_set_affinity is almost the last thing that
> happens in migrate_one_irq, and that for_each_active_irq loop is quite
> small too. So, there isn't much happening between the printk in
> irq_chip_redirect_set_affinity for the msi irq (which we do see in the
> log) and the printk in migrate_one_irq for the next irq (which we don't
> see).

This doesn't make any sense at all. irq_chip_redirect_set_affinity() is
only accessing interrupt descriptor associated memory and the new
redirection CPU is the same as the previous one as the mask changes from
0xff to 0x7f and therefore cpumask_first() yields 0 in both cases.

According to the provided dmesg, this happens on linux-next.

Jon, can you please validate that this happens as well on

     git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git irq/msi

Thanks

        tglx