linux-kernel - Re: [PATCH RT 5/8] sched: Fix affine_move

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Date:   Mon, 26 Jul 2021 14:39:27 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Pavel Machek <pavel@....cz>, Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        John Kacur <jkacur@...hat.com>, Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>,
        "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>, stable@...nel.org,
        "Peter Zijlstra \(Intel\)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH RT 5/8] sched: Fix affine_move_task() self-concurrency

On 25/07/21 07:03, Pavel Machek wrote:
> Hi!
>
>> 5.10.47-rt46-rc1 stable review patch.
>> If anyone has any objections, please let me know.
>>
>> Add set_affinity_pending::stop_pending, to indicate if a stopper is in
>> progress.
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 9cbe12d8c5bd..20588a59300d 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -1900,6 +1900,7 @@ struct migration_arg {
>>
>>  struct set_affinity_pending {
>>      refcount_t		refs;
>> +	unsigned int		stop_pending;
>>      struct completion	done;
>>      struct cpu_stop_work	stop_work;
>>      struct migration_arg	arg;
>
> For better readability, this should be bool, AFAICT.
>

It's intentionally declared as an int. sizeof(_Bool) is Implementation
Defined, so you can't sanely reason about struct layout.

There's been quite a few threads about this already, a quick search on lore
gave me:

https://lore.kernel.org/lkml/20180411081502.GJ4082@hirez.programming.kicks-ass.net/