Commit 3c426d5e authored Oct 16, 2012 by Tejun Heo

cgroup_freezer: don't stall transition to FROZEN for PF_NOFREEZE or PF_FREEZER_SKIP tasks



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

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@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>

parent 51f246ed

kernel/cgroup_freezer.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -214,11 +214,19 @@ static void update_if_frozen(struct cgroup *cgroup,

		cgroup_iter_start(cgroup, &it);
		while ((task = cgroup_iter_next(cgroup, &it))) {
		if (freezing(task)) {
		ntotal++;
		if (freezing(task) && (frozen(task) \|\|
		task_is_stopped_or_traced(task)))
		/*
		* 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) {
		BUG_ON(nfrozen > 0);