linux-kernel - Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU mask

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Message-ID: <20170406093224.q3tunb6gdx5a6flr@hirez.programming.kicks-ass.net>
Date:   Thu, 6 Apr 2017 11:32:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Mike Galbraith <efault@....de>, Ingo Molnar <mingo@...e.hu>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>
Subject: Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU
 mask

On Tue, Apr 04, 2017 at 08:42:02PM +0200, Sebastian Andrzej Siewior wrote:
> While converting the existing users I tried to stick with the rules
> above however… well mostly CPUFREQ tries to temporary switch the CPU
> mask to do something on a certain CPU and then switches the mask back it
> its original value.


There's a bunch of that through ancient and rotten parts of the kernel.
All those sites are broken.

Nothing stops userspace from setting a different affinity right after
the kernel does for those threads.