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Subject: Re: [PATCH v4 2/2] sched: Skip priority checks with
 SCHED_FLAG_KEEP_PARAMS
To:     Quentin Perret <qperret@google.com>
Cc:     mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org,
        qais.yousef@arm.com, rickyiu@google.com, wvw@google.com,
        patrick.bellasi@matbug.net, xuewen.yan94@gmail.com,
        linux-kernel@vger.kernel.org, kernel-team@android.com
References: <20210719161656.3833943-1-qperret@google.com>
 <20210719161656.3833943-3-qperret@google.com>
 <ad30be79-8fb2-023d-9936-01f7173164e4@arm.com> <YP6++lClPCQvTLcK@google.com>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <787ac8b6-3df6-0225-e835-c17a56a8d642@arm.com>
Date:   Thu, 29 Jul 2021 19:31:12 +0200
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On 26/07/2021 15:56, Quentin Perret wrote:
> On Thursday 22 Jul 2021 at 10:47:33 (+0200), Dietmar Eggemann wrote:

[...]

>>> @@ -7393,6 +7403,8 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
>>>  	rcu_read_unlock();
>>>  
>>>  	if (likely(p)) {
>>> +		if (attr.sched_flags & SCHED_FLAG_KEEP_PARAMS)
>>> +			get_params(p, &attr);
>>
>> SCHED_FLAG_KEEP_PARAMS is handled here but SCHED_FLAG_KEEP_POLICY
>> outside (before) the `if (likely(p))`?
> 
> Because I need to dereference p while SCHED_FLAG_KEEP_POLICY doesn't :)

Ah, true. Looked weird though.
But then the SCHED_FLAG_KEEP_POLICY condition can be placed closer to
the SCHED_FLAG_KEEP_PARAMS condition. We don't have to set
SETPARAM_POLICY if p == NULL.

>>>  		retval = sched_setattr(p, &attr);
>>>  		put_task_struct(p);
>>>  	}

[...]