[PATCH 4/7] cgroup_freezer: don't stall transition to FROZEN for PF_NOFREEZE or PF_FREEZER_SKIP tasks

From: Tejun Heo
Date: Tue Oct 16 2012 - 18:29:49 EST

cgroup_freezer doesn't transition from FREEZING to FROZEN if the
cgroup contains PF_NOFREEZE tasks or tasks sleeping with

Only kernel tasks can be non-freezable (PF_NOFREEZE) and there's
nothing cgroup_freezer or userland can do about or to it. It's
pointless to stall the transition for PF_NOFREEZE tasks.

PF_FREEZER_SKIP indicates that the task can be skipped when
determining whether frozen state is reached. A task with
PF_FREEZER_SKIP is guaranteed to perform try_to_freeze() after it
wakes up and can be considered frozen much like stopped or traced
tasks. Note that a vfork parent uses PF_FREEZER_SKIP while waiting
for the child.

This updates update_if_frozen() such that it only considers freezable
tasks and treats %true freezer_should_skip() tasks as frozen.

This allows cgroups w/ kthreads and vfork parents successfully reach
FROZEN state.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Rafael J. Wysocki <rjw@xxxxxxx>
kernel/cgroup_freezer.c | 16 ++++++++++++----
1 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 05d5218..557f367 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -214,10 +214,18 @@ static void update_if_frozen(struct cgroup *cgroup,

cgroup_iter_start(cgroup, &it);
while ((task = cgroup_iter_next(cgroup, &it))) {
- ntotal++;
- if (freezing(task) && (frozen(task) ||
- task_is_stopped_or_traced(task)))
- nfrozen++;
+ if (freezing(task)) {
+ ntotal++;
+ /*
+ * freezer_should_skip() indicates that the task
+ * should be skipped when determining freezing
+ * completion. Consider it frozen in addition to
+ * the usual frozen condition.
+ */
+ if (frozen(task) || task_is_stopped_or_traced(task) ||
+ freezer_should_skip(task))
+ nfrozen++;
+ }

if (old_state == CGROUP_THAWED) {

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