Message-ID: <alpine.DEB.2.20.1610172330350.6407@nanos>
Date:   Tue, 18 Oct 2016 00:01:01 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
cc:     "H. Peter Anvin" <h.peter.anvin@...el.com>,
        Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Nilay Vaish <nilayvaish@...il.com>, Shaohua Li <shli@...com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Sai Prakhya <sai.praneeth.prakhya@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v4 15/18] x86/intel_rdt: Add tasks files

On Fri, 14 Oct 2016, Fenghua Yu wrote:
> +struct task_move_callback {
> +	struct callback_head work;
> +	struct rdtgroup *rdtgrp;

Please align the struct members as you did everywhere else already.

> +};
> +
> +static void move_myself(struct callback_head *head)
> +{
> +	struct task_move_callback *callback;
> +	struct rdtgroup *rdtgrp;
> +
> +	callback = container_of(head, struct task_move_callback, work);
> +	rdtgrp = callback->rdtgrp;
> +
> +	/* Resource group might have been deleted before process runs */

  	/*
	 * If resource group was deleted before this task work callback
	 * was invoked, then assign the task to root group and free the
	 * resource group,
	 */

> +	if (atomic_dec_and_test(&rdtgrp->waitcount) &&
> +	    (rdtgrp->flags & RDT_DELETED)) {
> +		current->closid = 0;
> +		kfree(rdtgrp);
> +	}
> +
> +	kfree(callback);
> +}
> +
> +static int __rdtgroup_move_task(struct task_struct *tsk,
> +				struct rdtgroup *rdtgrp)
> +{
> +	struct task_move_callback *callback;
> +	int ret;
> +
> +	callback = kzalloc(sizeof(*callback), GFP_KERNEL);
> +	if (!callback)
> +		return -ENOMEM;
> +	callback->work.func = move_myself;
> +	callback->rdtgrp = rdtgrp;

Lacks a comment:

  	/*
	 * Take a refcount, so rdtgrp cannot be freed before the
	 * callback has been invoked
	 */

> +	atomic_inc(&rdtgrp->waitcount);
> +	ret = task_work_add(tsk, &callback->work, true);
> +	if (ret) {


Lacks a comment as well:

      		/*
		 * Task is exiting. Drop the refcount and free the callback.
		 * No need to check the refcount as the group cannot be
		 * deleted before the write function unlocks rdtgroup_mutex.
		 */

For you the comment might be obvious, but I had to lookup the world and
some more.

> +		atomic_dec(&rdtgrp->waitcount);
> +		kfree(callback);
> +	} else {
> +		tsk->closid = rdtgrp->closid;
> +	}
> +	return ret;

> +static int rdtgroup_task_write_permission(struct task_struct *task,
> +					  struct kernfs_open_file *of)
> +{
> +	const struct cred *cred = current_cred();
> +	const struct cred *tcred = get_task_cred(task);
> +	int ret = 0;
> +
> +	/*
> +	 * even if we're attaching all tasks in the thread group, we only

Sentences start with an uppercase letter.

> +	 * need to check permissions on one of them.
> +	 */
> +	if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
> +	    !uid_eq(cred->euid, tcred->uid) &&
> +	    !uid_eq(cred->euid, tcred->suid))
> +		ret = -EPERM;
> +
> +	put_cred(tcred);
> +	return ret;
> +}
> +
> +static int rdtgroup_move_task(pid_t pid, struct rdtgroup *rdtgrp,
> +			      struct kernfs_open_file *of)
> +{
> +	struct task_struct *tsk;
> +	int ret;
> +
> +	rcu_read_lock();
> +	if (pid) {
> +		tsk = find_task_by_vpid(pid);
> +		if (!tsk) {
> +			ret = -ESRCH;
> +			goto out_unlock_rcu;

This goto is pointless as this is the only user,

     	     	        rcu_read_unlock()l
			return -ESRCH;

> +		}
> +	} else {
> +		tsk = current;
> +	}

> @@ -559,6 +713,13 @@ static void rmdir_all_sub(void)
>  {
>  	struct rdtgroup *rdtgrp;
>  	struct list_head *l, *next;
> +	struct task_struct *p;
> +
> +	/* move all tasks to default resource group */
> +	read_lock(&tasklist_lock);
> +	for_each_process(p)
> +		p->closid = 0;
> +	read_unlock(&tasklist_lock);

Ok.

> +	/* Don't allow if there are processes in this group */
> +	read_lock(&tasklist_lock);
> +	for_each_process(p) {
> +		if (p->closid == rdtgrp->closid) {
> +			read_unlock(&tasklist_lock);
> +			rdtgroup_kn_unlock(kn);
> +			return -EBUSY;
> +		}
> +	}
> +	read_unlock(&tasklist_lock);

I wonder, whether we should simply give those tasks back to the default
group, same as we do with the cpus.

Thanks,

	tglx

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