From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: Re: [regression] cpuset: offlined CPUs removed from affinity masks
Date: Wed, 19 Feb 2020 10:47:40 -0500
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To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Li Zefan <lizefan@huawei.com>, cgroups <cgroups@vger.kernel.org>, linux-kernel <linux-kernel@vger.kernel.org>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Valentin Schneider <valentin.schneider@arm.com>

On Wed, Feb 19, 2020 at 10:43:05AM -0500, Mathieu Desnoyers wrote:
> The regression I'm talking about here is that CONFIG_CPUSET=y changes the
> behavior of the sched_setaffinify system call, which existed prior to
> cpusets.
> 
> sched_setaffinity should behave in the same way for kernels configured with
> CONFIG_CPUSET=y or CONFIG_CPUSET=n.
> 
> The fact that cpuset decides to irreversibly change the task affinity mask
> may not be considered a regression if it has always done that, but changing
> the behavior of sched_setaffinity seems to fit the definition of a regression.

We generally use "regression" for breakages which weren't in past
versions but then appeared later. It has debugging implications
because if we know something is a regression, we generally can point
to the commit which introduced the bug either through examining the
history or bisection.

It is a silly bug, for sure, but slapping regression name on it just
confuses rather than helping anything.

-- 
tejun