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Commit 892a2b90 authored by Mandeep Singh Baines's avatar Mandeep Singh Baines Committed by Tejun Heo
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cgroup: only need to check oldcgrp==newgrp once 



In cgroup_attach_proc it is now sufficient to only check that
oldcgrp==newcgrp once. Now that we are using threadgroup_lock()
during the migrations, oldcgrp will not change.

Signed-off-by: default avatarMandeep Singh Baines <msb@chromium.org>
Acked-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: containers@lists.linux-foundation.org
Cc: cgroups@vger.kernel.org
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
parent b07ef774

kernel/cgroup.c

+6 −16
Original line number Diff line number Diff line
@@ -2067,7 +2067,7 @@ static int css_set_prefetch(struct cgroup *cgrp, struct css_set *cg, 
 */

int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)

{

	int retval, i, group_size, nr_migrating_tasks;

	int retval, i, group_size;

	struct cgroup_subsys *ss, *failed_ss = NULL;

	/* guaranteed to be initialized later, but the compiler needs this */

	struct css_set *oldcg;
@@ -2118,7 +2118,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
	}



	tsk = leader;

	i = nr_migrating_tasks = 0;

	i = 0;

	do {

		struct task_and_cgroup ent;
@@ -2134,11 +2134,12 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
		 */

		ent.task = tsk;

		ent.cgrp = task_cgroup_from_root(tsk, root);

		/* nothing to do if this task is already in the cgroup */

		if (ent.cgrp == cgrp)

			continue;

		retval = flex_array_put(group, i, &ent, GFP_ATOMIC);

		BUG_ON(retval != 0);

		i++;

		if (ent.cgrp != cgrp)

			nr_migrating_tasks++;

	} while_each_thread(leader, tsk);

	/* remember the number of threads in the array for later. */

	group_size = i;
@@ -2148,7 +2149,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 


	/* methods shouldn't be called if no task is actually migrating */

	retval = 0;

	if (!nr_migrating_tasks)

	if (!group_size)

		goto out_free_group_list;



	/*
@@ -2171,14 +2172,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
	INIT_LIST_HEAD(&newcg_list);

	for (i = 0; i < group_size; i++) {

		tc = flex_array_get(group, i);

		/* nothing to do if this task is already in the cgroup */

		if (tc->cgrp == cgrp)

			continue;

		/*

		 * get old css_set pointer. threadgroup is locked so this is

		 * safe against concurrent cgroup_exit() changing this to

		 * init_css_set.

		 */

		oldcg = tc->task->cgroups;



		/* if we don't already have it in the list get a new one */
@@ -2194,9 +2187,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
	 */

	for (i = 0; i < group_size; i++) {

		tc = flex_array_get(group, i);

		/* leave current thread as it is if it's already there */

		if (tc->cgrp == cgrp)

			continue;

		retval = cgroup_task_migrate(cgrp, tc->cgrp, tc->task, true);

		BUG_ON(retval);

	}