Re: [PATCH] genirq: Update effective affinity for redirected interrupts

[Jon Hunter <jonathanh@nvidia.com>]

On 12/01/2026 21:14, Radu Rendec wrote:
> For redirected interrupts, irq_chip_redirect_set_affinity() does not
> update the effective affinity mask, which then triggers the warning in
> irq_validate_effective_affinity(). Also, because the effective affinity
> mask is empty, the cpumask_test_cpu(smp_processor_id(), m) condition in
> demux_redirect_remote() is always false, and the interrupt is always
> redirected, even if it's already running on the target CPU.
> 
> Set the effective affinity mask to be the same as the requested affinity
> mask. It's worth noting that irq_do_set_affinity() filters out offline
> CPUs before calling chip->irq_set_affinity() (unless `force` is set), so
> the mask passed to irq_chip_redirect_set_affinity() is already filtered.
> 
> The solution is not ideal because it may lie about the effective
> affinity of the demultiplexed ("child") interrupt. If the requested
> affinity mask includes multiple CPUs, the effective affinity, in
> reality, is the intersection between the requested mask and the
> demultiplexing ("parent") interrupt's effective affinity mask, plus
> the first CPU in the requested mask.
> 
> Accurately describing the effective affinity of the demultiplexed
> interrupt is not trivial because it requires keeping track of the
> demultiplexing interrupt's effective affinity. That is tricky in the
> context of CPU hot(un)plugging, where interrupt migration ordering is
> not guaranteed. The solution in the initial version of the fixed patch,
> which stored the first CPU of the demultiplexing interrupt's effective
> affinity in the `target_cpu` field, has its own drawbacks and
> limitations.
> 
> Fixes: fcc1d0dabdb6 ("genirq: Add interrupt redirection infrastructure")
> Reported-by: Jon Hunter <jonathanh@nvidia.com>
> Closes: https://lore.kernel.org/all/44509520-f29b-4b8a-8986-5eae3e022eb7@nvidia.com/
> Signed-off-by: Radu Rendec <rrendec@redhat.com>
> ---
>   kernel/irq/chip.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
> index 433f1dd2b0ca7..35bc17bc369e0 100644
> --- a/kernel/irq/chip.c
> +++ b/kernel/irq/chip.c
> @@ -1493,6 +1493,8 @@ int irq_chip_redirect_set_affinity(struct irq_data *data, const struct cpumask *
>   	struct irq_redirect *redir = &irq_data_to_desc(data)->redirect;
>   
>   	WRITE_ONCE(redir->target_cpu, cpumask_first(dest));
> +	irq_data_update_effective_affinity(data, dest);
> +
>   	return IRQ_SET_MASK_OK;
>   }
>   EXPORT_SYMBOL_GPL(irq_chip_redirect_set_affinity);


This is working for me ...

Tested-by: Jon Hunter <jonathanh@nvidia.com>

Thanks
Jon

-- 
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