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Commit cb0f1fe9 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: move css_set_rwsem locking outside of cgroup_task_migrate() 



Instead of repeatedly locking and unlocking css_set_rwsem inside
cgroup_task_migrate(), update cgroup_attach_task() to grab it outside
of the loop and update cgroup_task_migrate() to use
put_css_set_locked().

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 89c5509b

kernel/cgroup.c

+11 −5
Original line number Diff line number Diff line
@@ -1715,10 +1715,13 @@ int cgroup_taskset_size(struct cgroup_taskset *tset) 
EXPORT_SYMBOL_GPL(cgroup_taskset_size);





/*

/**

 * cgroup_task_migrate - move a task from one cgroup to another.

 * @old_cgrp; the cgroup @tsk is being migrated from

 * @tsk: the task being migrated

 * @new_cset: the new css_set @tsk is being attached to

 *

 * Must be called with cgroup_mutex and threadgroup locked.

 * Must be called with cgroup_mutex, threadgroup and css_set_rwsem locked.

 */

static void cgroup_task_migrate(struct cgroup *old_cgrp,

				struct task_struct *tsk,
@@ -1726,6 +1729,9 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp, 
{

	struct css_set *old_cset;



	lockdep_assert_held(&cgroup_mutex);

	lockdep_assert_held(&css_set_rwsem);



	/*

	 * We are synchronized through threadgroup_lock() against PF_EXITING

	 * setting such that we can't race against cgroup_exit() changing the
@@ -1738,9 +1744,7 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp, 
	rcu_assign_pointer(tsk->cgroups, new_cset);

	task_unlock(tsk);



	down_write(&css_set_rwsem);

	list_move(&tsk->cg_list, &new_cset->tasks);

	up_write(&css_set_rwsem);



	/*

	 * We just gained a reference on old_cset by taking it from the
@@ -1748,7 +1752,7 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp, 
	 * we're safe to drop it here; it will be freed under RCU.

	 */

	set_bit(CGRP_RELEASABLE, &old_cgrp->flags);

	put_css_set(old_cset, false);

	put_css_set_locked(old_cset, false);

}



/**
@@ -1871,10 +1875,12 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk, 
	 * proceed to move all tasks to the new cgroup.  There are no

	 * failure cases after here, so this is the commit point.

	 */

	down_write(&css_set_rwsem);

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

		tc = flex_array_get(group, i);

		cgroup_task_migrate(tc->cgrp, tc->task, tc->cset);

	}

	up_write(&css_set_rwsem);

	/* nothing is sensitive to fork() after this point. */



	/*