cgroup: make css_sets pin the associated cgroups (2ceb231b) · Commits · 戴 / test

Currently, css_sets don't pin the associated cgroups. This is okay as a cgroup with css_sets associated are not allowed to be removed; however, to help resource tracking for zombie tasks, this is scheduled to change such that a cgroup can be removed even when it has css_sets associated as long as none of them are populated. To ensure that a cgroup doesn't go away while css_sets are still associated with it, make each associated css_set hold a reference on the cgroup if non-root. v2: Root cgroups are special and shouldn't be ref'd by css_sets. Signed-off-by:

Tejun Heo <tj@kernel.org>

kernel/cgroup.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -705,6 +705,8 @@ static void put_css_set_locked(struct css_set *cset)
		list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
		list_del(&link->cset_link);
		list_del(&link->cgrp_link);
		if (cgroup_parent(link->cgrp))
		cgroup_put(link->cgrp);
		kfree(link);
		}

		@@ -919,6 +921,9 @@ static void link_css_set(struct list_head tmp_links, struct css_set cset,
		* is sorted by order of hierarchy creation
		*/
		list_add_tail(&link->cgrp_link, &cset->cgrp_links);

		if (cgroup_parent(cgrp))
		cgroup_get(cgrp);
		}

		/**
		@@ -4998,10 +5003,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)

		lockdep_assert_held(&cgroup_mutex);

		/*
		* css_set_rwsem synchronizes access to ->cset_links and prevents
		* @cgrp from being removed while put_css_set() is in progress.
		*/
		/* css_set_rwsem synchronizes access to ->cset_links */
		down_read(&css_set_rwsem);
		empty = list_empty(&cgrp->cset_links);
		up_read(&css_set_rwsem);

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