linux-kernel - Re: [PATCH v5] workqueue: Fix edge cases for calc of pool's cpumask

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Message-ID: <20170727175834.GG742618@devbig577.frc2.facebook.com>
Date:   Thu, 27 Jul 2017 13:58:35 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Michael Bringmann <mwb@...ux.vnet.ibm.com>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, nfont@...ux.vnet.ibm.com
Subject: Re: [PATCH v5] workqueue: Fix edge cases for calc of pool's cpumask

Hello, Michael.

On Thu, Jul 27, 2017 at 12:06:22PM -0500, Michael Bringmann wrote:
> 
> On NUMA systems with dynamic processors, the content of the cpumask
> may change over time.  As new processors are added via DLPAR operations,
> workqueues are created for them.  Depending upon the order in which CPUs
> are added/removed, we may run into problems with the content of the
> cpumask used by the workqueues.  This patch deals with situations where
> the online cpumask for a node is a proper superset of possible cpumask
> for the node.  It also deals with edge cases where the order in which
> CPUs are removed/added from the online cpumask may leave the set for a
> node empty, and require execution by CPUs on another node.

I think we already talked about this before but can you please note
that this is a bandaid to workaround an underlying bug.  This isn't
something which normally happens on NUMA sytems with dynamic
processors.  This is bandaiding a hole so that the machine at least
doesn't crash immediately until we can get the underlying problem
fixed properly.

Thanks.

-- 
tejun