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Commit 026085ef authored by Mandeep Singh Baines's avatar Mandeep Singh Baines Committed by Tejun Heo
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cgroup: remove redundant get/put of old css_set from migrate 

We can now assume that the css_set reference held by the task
will not go away for an exiting task. PF_EXITING state can be
trusted throughout migration by checking it after locking
threadgroup.

Changes in V4:
* https://lkml.org/lkml/2011/12/20/368 (Tejun Heo)
  * Fix typo in commit message
  * Undid the rename of css_set_check_fetched
* https://lkml.org/lkml/2011/12/20/427 (Li Zefan)
  * Fix comment in cgroup_task_migrate()
Changes in V3:
* https://lkml.org/lkml/2011/12/20/255 (Frederic Weisbecker)
  * Fixed to put error in retval
Changes in V2:
* https://lkml.org/lkml/2011/12/19/289

 (Tejun Heo)
  * Updated commit message

-tj: removed stale patch description about dropped function rename.

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 c84cdf75

kernel/cgroup.c

+8 −20
Original line number Diff line number Diff line
@@ -1850,14 +1850,12 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, 
	struct css_set *newcg;



	/*

	 * get old css_set. We are synchronized through threadgroup_lock()

	 * against PF_EXITING setting such that we can't race against

	 * cgroup_exit() changing the css_set to init_css_set and dropping the

	 * old one.

	 * We are synchronized through threadgroup_lock() against PF_EXITING

	 * setting such that we can't race against cgroup_exit() changing the

	 * css_set to init_css_set and dropping the old one.

	 */

	WARN_ON_ONCE(tsk->flags & PF_EXITING);

	oldcg = tsk->cgroups;

	get_css_set(oldcg);



	/* locate or allocate a new css_set for this task. */

	if (guarantee) {
@@ -1872,12 +1870,9 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, 
		might_sleep();

		/* find_css_set will give us newcg already referenced. */

		newcg = find_css_set(oldcg, cgrp);

		if (!newcg) {

			put_css_set(oldcg);

		if (!newcg)

			return -ENOMEM;

	}

	}

	put_css_set(oldcg);



	task_lock(tsk);

	rcu_assign_pointer(tsk->cgroups, newcg);
@@ -2186,19 +2181,12 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
		 * init_css_set.

		 */

		oldcg = tc->task->cgroups;

		get_css_set(oldcg);

		/* see if the new one for us is already in the list? */

		if (css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list)) {

			/* was already there, nothing to do. */

			put_css_set(oldcg);

		} else {

			/* we don't already have it. get new one. */

			retval = css_set_prefetch(cgrp, oldcg, &newcg_list);

			put_css_set(oldcg);

			if (retval)



		/* if we don't already have it in the list get a new one */

		if (!css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list))

			if (retval = css_set_prefetch(cgrp, oldcg, &newcg_list))

				goto out_list_teardown;

	}

	}



	/*

	 * step 3: now that we're guaranteed success wrt the css_sets,