path: root/kernel/fork.c
diff options
authorTejun Heo <>2015-10-15 16:41:53 -0400
committerTejun Heo <>2015-10-15 16:41:53 -0400
commit2e91fa7f6d451e3ea9fec999065d2fd199691f9d (patch)
tree9869ef4bca569d824ba3266e5b2373302356bea3 /kernel/fork.c
parentf0d9a5f175753a371bc7fdff0d584a8d9cd72bb0 (diff)
cgroup: keep zombies associated with their original cgroups
cgroup_exit() is called when a task exits and disassociates the exiting task from its cgroups and half-attach it to the root cgroup. This is unnecessary and undesirable. No controller actually needs an exiting task to be disassociated with non-root cgroups. Both cpu and perf_event controllers update the association to the root cgroup from their exit callbacks just to keep consistent with the cgroup core behavior. Also, this disassociation makes it difficult to track resources held by zombies or determine where the zombies came from. Currently, pids controller is completely broken as it uncharges on exit and zombies always escape the resource restriction. With cgroup association being reset on exit, fixing it is pretty painful. There's no reason to reset cgroup membership on exit. The zombie can be removed from its css_set so that it doesn't show up on "cgroup.procs" and thus can't be migrated or interfere with cgroup removal. It can still pin and point to the css_set so that its cgroup membership is maintained. This patch makes cgroup core keep zombies associated with their cgroups at the time of exit. * Previous patches decoupled populated_cnt tracking from css_set lifetime, so a dying task can be simply unlinked from its css_set while pinning and pointing to the css_set. This keeps css_set association from task side alive while hiding it from "cgroup.procs" and populated_cnt tracking. The css_set reference is dropped when the task_struct is freed. * ->exit() callback no longer needs the css arguments as the associated css never changes once PF_EXITING is set. Removed. * cpu and perf_events controllers no longer need ->exit() callbacks. There's no reason to explicitly switch away on exit. The final schedule out is enough. The callbacks are removed. * On traditional hierarchies, nothing changes. "/proc/PID/cgroup" still reports "/" for all zombies. On the default hierarchy, "/proc/PID/cgroup" keeps reporting the cgroup that the task belonged to at the time of exit. If the cgroup gets removed before the task is reaped, " (deleted)" is appended. v2: Build brekage due to missing dummy cgroup_free() when !CONFIG_CGROUP fixed. Signed-off-by: Tejun Heo <> Cc: Ingo Molnar <> Cc: Peter Zijlstra <> Cc: Arnaldo Carvalho de Melo <>
Diffstat (limited to 'kernel/fork.c')
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 7d5f0f118a63..118743bb5964 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -251,6 +251,7 @@ void __put_task_struct(struct task_struct *tsk)
WARN_ON(tsk == current);
+ cgroup_free(tsk);