summaryrefslogtreecommitdiff
path: root/include/linux/cgroup-defs.h
diff options
context:
space:
mode:
authorRoman Gushchin <guro@fb.com>2019-04-19 10:03:03 -0700
committerTejun Heo <tj@kernel.org>2019-04-19 11:26:48 -0700
commit4dcabece4c3a9f9522127be12cc12cc120399b2f (patch)
tree0d985b3d1232ff76e67a0ac07213e4c8e4ab4a7b /include/linux/cgroup-defs.h
parentaade7f9efba098859681f8e88d81a5b44ad09b12 (diff)
cgroup: protect cgroup->nr_(dying_)descendants by css_set_lock
The number of descendant cgroups and the number of dying descendant cgroups are currently synchronized using the cgroup_mutex. The number of descendant cgroups will be required by the cgroup v2 freezer, which will use it to determine if a cgroup is frozen (depending on total number of descendants and number of frozen descendants). It's not always acceptable to grab the cgroup_mutex, especially from quite hot paths (e.g. exit()). To avoid this, let's additionally synchronize these counters using the css_set_lock. So, it's safe to read these counters with either cgroup_mutex or css_set_lock locked, and for changing both locks should be acquired. Signed-off-by: Roman Gushchin <guro@fb.com> Signed-off-by: Tejun Heo <tj@kernel.org> Cc: kernel-team@fb.com
Diffstat (limited to 'include/linux/cgroup-defs.h')
-rw-r--r--include/linux/cgroup-defs.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 1c70803e9f77..7d57890cec67 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -349,6 +349,11 @@ struct cgroup {
* Dying cgroups are cgroups which were deleted by a user,
* but are still existing because someone else is holding a reference.
* max_descendants is a maximum allowed number of descent cgroups.
+ *
+ * nr_descendants and nr_dying_descendants are protected
+ * by cgroup_mutex and css_set_lock. It's fine to read them holding
+ * any of cgroup_mutex and css_set_lock; for writing both locks
+ * should be held.
*/
int nr_descendants;
int nr_dying_descendants;