linux-kernel - Re: [PATCH-tip v3] sched: Use kfree_rcu() in do_set_cpus

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Message-ID: <828245eb-66ee-a2e3-c9ab-7cbc90044de3@redhat.com>
Date:   Thu, 22 Dec 2022 16:03:31 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Phil Auld <pauld@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH-tip v3] sched: Use kfree_rcu() in do_set_cpus_allowed()


On 12/22/22 15:25, Peter Zijlstra wrote:
> On Thu, Dec 22, 2022 at 03:18:29PM -0500, Waiman Long wrote:
>
>>>> @@ -8220,7 +8230,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
>>>>    	struct affinity_context ac;
>>>>    	struct cpumask *user_mask;
>>>>    	struct task_struct *p;
>>>> -	int retval;
>>>> +	int retval, size;
>>>>    	rcu_read_lock();
>>>> @@ -8253,7 +8263,11 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
>>>>    	if (retval)
>>>>    		goto out_put_task;
>>>> -	user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
>>>> +	/*
>>>> +	 * See do_set_cpus_allowed() for the rcu_head usage.
>>>> +	 */
>>>> +	size = max_t(int, cpumask_size(), sizeof(struct rcu_head));
>>>> +	user_mask = kmalloc(size, GFP_KERNEL);
>>>>    	if (!user_mask) {
>>>>    		retval = -ENOMEM;
>>>>    		goto out_put_task;
>>> AFAICT you forgot dup_user_cpus_ptr().
>> I haven't received any response from you for a while. So it is just a ping.
> I was out sick :/

I am sorry to hear that. Hope you are all right now.


>
>> Of course, I am aware that there is another dup_user_cpus_ptr() patch
>> ouststanding. I will of course talk about that when you respond. I also have
>> a pending rwsem patch series waiting for your review:-)
> The point was that dup_user_cpus_ptr() also does an allocation and needs
> to allocate the possibly bigger size too, no?

Oh, yes. I missed that. I will combine the two patches into a patch series.

Thanks,
Longman