>From 12ab687370ca062d263848b52515c839809383aa Mon Sep 17 00:00:00 2001
From: Tejun Heo <t...@kernel.org>
Date: Wed, 14 Oct 2015 21:31:40 -0400
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 <t...@kernel.org>
---
kernel/cgroup.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ab5c9a5..ea87340 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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);
--
2.4.3
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