Message-ID: <820b04a1-8c2f-ba81-f508-5750c63f3239@redhat.com>
Date:   Fri, 3 Feb 2023 17:13:02 -0500
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Subject: Re: [PATCH] sched/core: Fix a missed update of user_cpus_ptr
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To:     Tejun Heo <tj@kernel.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Will Deacon <will@kernel.org>, Phil Auld <pauld@redhat.com>,
        linux-kernel@vger.kernel.org
References: <20230203181849.221943-1-longman@redhat.com>
 <Y9128uN5X8L3VTG3@slm.duckdns.org>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <Y9128uN5X8L3VTG3@slm.duckdns.org>
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On 2/3/23 16:04, Tejun Heo wrote:
> On Fri, Feb 03, 2023 at 01:18:49PM -0500, Waiman Long wrote:
>> Since commit 8f9ea86fdf99 ("sched: Always preserve the user requested
>> cpumask"), a successful call to sched_setaffinity() should always save
>> the user requested cpu affinity mask in a task's user_cpus_ptr. However,
>> when the given cpu mask is the same as the current one, user_cpus_ptr
>> is not updated. Fix this by saving the user mask in this case too.
>>
>> Fixes: 8f9ea86fdf99 ("sched: Always preserve the user requested cpumask")
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>>   kernel/sched/core.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 30d9752e2ca5..91255f791df3 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -2951,8 +2951,11 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
>>   	}
>>   
>>   	if (!(ctx->flags & SCA_MIGRATE_ENABLE)) {
>> -		if (cpumask_equal(&p->cpus_mask, ctx->new_mask))
>> +		if (cpumask_equal(&p->cpus_mask, ctx->new_mask)) {
>> +			if (ctx->flags & SCA_USER)
>> +				swap(p->user_cpus_ptr, ctx->user_mask);
>>   			goto out;
>> +		}
>>   
>>   		if (WARN_ON_ONCE(p == current &&
>>   				 is_migration_disabled(p) &&
> and this is for a separate bug and should go through the scheduler tree.

Yes, this is for Peter to pick up.

Cheers,
Longman