linux-kernel - Re: irq/affinity: Fix extra vecs calculation

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Message-ID: <20170419170359.GE16224@localhost.localdomain>
Date:   Wed, 19 Apr 2017 13:03:59 -0400
From:   Keith Busch <keith.busch@...el.com>
To:     Andrei Vagin <avagin@...tuozzo.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Xiaolong Ye <xiaolong.ye@...el.com>
Subject: Re: irq/affinity: Fix extra vecs calculation

On Wed, Apr 19, 2017 at 09:20:27AM -0700, Andrei Vagin wrote:
> Hi,
> 
> Something is wrong with this patch. We run CRIU tests for upstream kernels.
> And we found that a kernel with this patch can't be booted.
> 
> https://travis-ci.org/avagin/linux/builds/223557750
> 
> We don't have access to console logs and I can't reproduce this issue on
> my nodes. I tired to revert this patch and everything works as expected.
> 
> https://travis-ci.org/avagin/linux/builds/223594172
> 
> Here is another report about this patch
> https://lkml.org/lkml/2017/4/16/344

Yikes, okay, I've made a mistake somewhere. Sorry about that, I will
look into this ASAP.

If it's a divide by 0 as your last link indicates, that must mean there
are possible nodes, but have no CPUs, and those should be skipped. If
that's the case, the following should fix it, but I'm going to do some
more qemu testing with various CPU topologies to confirm.

---
diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index d052947..80c45d0 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -105,6 +105,9 @@ irq_create_affinity_masks(int nvecs, const struct irq_affinity *affd)
 
 		/* Calculate the number of cpus per vector */
 		ncpus = cpumask_weight(nmsk);
+		if (!ncpus)
+			continue;
+
 		vecs_to_assign = min(vecs_per_node, ncpus);
 
 		/* Account for rounding errors */
--