Hi,
I'm trying to understand now why I did that change in
2d3cbf8bc (the bug itself was in the if-the-else clause in
update_if_frozen , anyway).
Well, when I look at this now I think that there is nothing wrong with
your patch.
You can try my testcases from 2d3cbf8bc and 0bdba580, but it should be ok.
One thing I am not sure completely of is the following situation. So the
group is frozen
with the STOPPED task inside. There are few questions:
* if you send SIGCONT to the task now, will it wake up?
* if yes - will it get *immediately* frozen?
I im going to check it myself, but maybe you can answer faster :).
Tomek
Le 16/11/2011 22:50, Michal Hocko a écrit :
2d3cbf8b (cgroup_freezer: update_freezer_state() does incorrect state
transitions) removed is_task_frozen_enough and replaced it with a simple
frozen call. This, however, breaks freezing for a group with stopped tasks
because those cannot be frozen and so the group remains in CGROUP_FREEZING
state (update_if_frozen doesn't count stopped tasks) and never reaches
CGROUP_FROZEN.
Let's add is_task_frozen_enough back and use it at the original locations
(update_if_frozen and try_to_freeze_cgroup). Semantically we consider
stopped tasks as frozen enough so we should consider both cases when
testing frozen tasks.
Testcase:
mkdir /dev/freezer
mount -t cgroup -o freezer none /dev/freezer
mkdir /dev/freezer/foo
sleep 1h&
pid=$!
kill -STOP $pid
echo $pid> /dev/freezer/foo/tasks
echo FROZEN> /dev/freezer/foo/freezer.state
while true
do
cat /dev/freezer/foo/freezer.state
[ "`cat /dev/freezer/foo/freezer.state`" = "FROZEN" ]&& break
sleep 1
done
echo OK
Signed-off-by: Michal Hocko<mhocko@xxxxxxx>
Cc: Tomasz Buchert<tomasz.buchert@xxxxxxxx>
Cc: Paul Menage<paul@xxxxxxxxxxxxxx>
Cc: Li Zefan<lizf@xxxxxxxxxxxxxx>
Cc: Andrew Morton<akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Tejun Heo<htejun@xxxxxxxxx>
---
kernel/cgroup_freezer.c | 11 +++++++++--
1 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 5e828a2..4d073dc 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -153,6 +153,13 @@ static void freezer_destroy(struct cgroup_subsys *ss,
kfree(cgroup_freezer(cgroup));
}
+/* Task is frozen or will freeze immediately when next it gets woken */
+static bool is_task_frozen_enough(struct task_struct *task)
+{
+ return frozen(task) ||
+ (task_is_stopped_or_traced(task)&& freezing(task));
+}
+
/*
* The call to cgroup_lock() in the freezer.state write method prevents
* a write to that file racing against an attach, and hence the
@@ -231,7 +238,7 @@ static void update_if_frozen(struct cgroup *cgroup,
cgroup_iter_start(cgroup,&it);
while ((task = cgroup_iter_next(cgroup,&it))) {
ntotal++;
- if (frozen(task))
+ if (is_task_frozen_enough(task))
nfrozen++;
}
@@ -284,7 +291,7 @@ static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
while ((task = cgroup_iter_next(cgroup,&it))) {
if (!freeze_task(task, true))
continue;
- if (frozen(task))
+ if (is_task_frozen_enough(task))
continue;
if (!freezing(task)&& !freezer_should_skip(task))
num_cant_freeze_now++;
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