linux-kernel - Re: [PATCH RT 2/8] sched: __set_cpus_allowed_ptr: Check cpus_mask, not cpus

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Message-ID: <1bcdec32b7a8165935cffbb2547c3d977c93f26d.camel@redhat.com>
Date:   Tue, 17 Sep 2019 10:23:58 -0500
From:   Scott Wood <swood@...hat.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Clark Williams <williams@...hat.com>,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH RT 2/8] sched: __set_cpus_allowed_ptr: Check cpus_mask,
 not cpus_ptr

On Tue, 2019-09-17 at 16:57 +0200, Sebastian Andrzej Siewior wrote:
> On 2019-07-27 00:56:32 [-0500], Scott Wood wrote:
> > This function is concerned with the long-term cpu mask, not the
> > transitory mask the task might have while migrate disabled.  Before
> > this patch, if a task was migrate disabled at the time
> > __set_cpus_allowed_ptr() was called, and the new mask happened to be
> > equal to the cpu that the task was running on, then the mask update
> > would be lost.
> 
> lost as in "would not be carried out" I assume.

Right.  The old mask would be restored upon migrate_enable() even though
that's no longer the policy that was requested.

-Scott