linux-kernel - Re: [PATCH] x86/apic/vector: Fix ordering in vector assignment

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Message-ID: <20201211135025.GA6520@xz-x1>
Date:   Fri, 11 Dec 2020 08:50:25 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Shung-Hsi Yu <shung-hsi.yu@...e.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH] x86/apic/vector: Fix ordering in vector assignment

On Thu, Dec 10, 2020 at 09:18:22PM +0100, Thomas Gleixner wrote:
> Prarit reported that depending on the affinity setting the
> 
>  ' irq $N: Affinity broken due to vector space exhaustion.'
> 
> message is showing up in dmesg, but the vector space on the CPUs in the
> affinity mask is definitely not exhausted.
> 
> Shung-Hsi provided traces and analysis which pinpoints the problem:
> 
> The ordering of trying to assign an interrupt vector in
> assign_irq_vector_any_locked() is simply wrong if the interrupt data has a
> valid node assigned. It does:
> 
>  1) Try the intersection of affinity mask and node mask
>  2) Try the node mask
>  3) Try the full affinity mask
>  4) Try the full online mask
> 
> Obviously #2 and #3 are in the wrong order as the requested affinity
> mask has to take precedence.
> 
> In the observed cases #1 failed because the affinity mask did not contain
> CPUs from node 0. That made it allocate a vector from node 0, thereby
> breaking affinity and emitting the misleading message.
> 
> Revert the order of #2 and #3 so the full affinity mask without the node
> intersection is tried before actually affinity is broken.
> 
> If no node is assigned then only the full affinity mask and if that fails
> the full online mask is tried.
> 
> Fixes: d6ffc6ac83b1 ("x86/vector: Respect affinity mask in irq descriptor")
> Reported-by: Shung-Hsi Yu <shung-hsi.yu@...e.com>
> Reported-by: Prarit Bhargava <prarit@...hat.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Shung-Hsi Yu <shung-hsi.yu@...e.com>
> Cc: stable@...r.kernel.org

Reviewed-by: Peter Xu <peterx@...hat.com>

-- 
Peter Xu