linux-kernel - RE: [PATCH] x86: Add check for number of available vectors before CPU down

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Date:	Tue, 3 Dec 2013 23:42:19 +0000
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	Prarit Bhargava <prarit@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCH] x86: Add check for number of available vectors before
 CPU down



> -----Original Message-----
> From: Prarit Bhargava [mailto:prarit@...hat.com]
> 
> Second try at this ...
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=64791
> 
> When a cpu is downed on a system, the irqs on the cpu are assigned to
> other cpus.  It is possible, however, that when a cpu is downed there
> aren't enough free vectors on the remaining cpus to account for the
> vectors from the cpu that is being downed.
> 
> This results in an interesting "overflow" condition where irqs are
> "assigned" to a CPU but are not handled.
> 
> For example, when downing cpus on a 1-64 logical processor system:
> 
> +			if (per_cpu(vector_irq, cpu)[vector] < 0)
> +				count++;

But later on fixup_irqs will set some of vector_irq vector as -1 on this
to-be-disabled cpu. That will release vectors assigned to this cpu. So
checking vector_irq at this point before fixup_irqs doesn't make sense, right?

Thanks.

-Fenghua

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