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Date: Fri, 19 Aug 2011 16:16:19 +0200
From: Tejun Heo <tj@...nel.org>
To: rjw@...k.pl, menage@...gle.com, linux-kernel@...r.kernel.org
Cc: arnd@...db.de, oleg@...hat.com, Tejun Heo <tj@...nel.org>,
Li Zefan <lizf@...fujitsu.com>
Subject: [PATCH 13/16] cgroup_freezer: prepare for removal of TIF_FREEZE
TIF_FREEZE will be removed soon and freezing() will directly test
whether any freezing condition is in effect. Make the following
changes in preparation.
* Rename cgroup_freezing_or_frozen() to cgroup_freezing() and make it
return bool.
* Make cgroup_freezing() access task_freezer() under rcu read lock
instead of task_lock(). This makes the state dereferencing racy
against task moving to another cgroup; however, it was already racy
without this change as ->state dereference wasn't synchronized.
This will be later dealt with using attach hooks.
* freezer->state is now set before trying to push tasks into the
target state.
Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Paul Menage <menage@...gle.com>
Cc: Li Zefan <lizf@...fujitsu.com>
---
include/linux/freezer.h | 6 +++---
kernel/cgroup_freezer.c | 36 ++++++++++++------------------------
kernel/power/process.c | 2 +-
3 files changed, 16 insertions(+), 28 deletions(-)
diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index 13559a8..bcc0637 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -63,11 +63,11 @@ extern bool freeze_task(struct task_struct *p, bool sig_only);
extern bool __set_freezable(bool with_signal);
#ifdef CONFIG_CGROUP_FREEZER
-extern int cgroup_freezing_or_frozen(struct task_struct *task);
+extern bool cgroup_freezing(struct task_struct *task);
#else /* !CONFIG_CGROUP_FREEZER */
-static inline int cgroup_freezing_or_frozen(struct task_struct *task)
+static inline bool cgroup_freezing(struct task_struct *task)
{
- return 0;
+ return false;
}
#endif /* !CONFIG_CGROUP_FREEZER */
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e7fa0ec..0478c35 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -48,19 +48,17 @@ static inline struct freezer *task_freezer(struct task_struct *task)
struct freezer, css);
}
-static inline int __cgroup_freezing_or_frozen(struct task_struct *task)
+bool cgroup_freezing(struct task_struct *task)
{
- enum freezer_state state = task_freezer(task)->state;
- return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN);
-}
+ enum freezer_state state;
+ bool ret;
-int cgroup_freezing_or_frozen(struct task_struct *task)
-{
- int result;
- task_lock(task);
- result = __cgroup_freezing_or_frozen(task);
- task_unlock(task);
- return result;
+ rcu_read_lock();
+ state = task_freezer(task)->state;
+ ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN;
+ rcu_read_unlock();
+
+ return ret;
}
/*
@@ -102,9 +100,6 @@ struct cgroup_subsys freezer_subsys;
* freezer_can_attach():
* cgroup_mutex (held by caller of can_attach)
*
- * cgroup_freezing_or_frozen():
- * task->alloc_lock (to get task's cgroup)
- *
* freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
* freezer->lock
* sighand->siglock (if the cgroup is freezing)
@@ -177,13 +172,7 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
- rcu_read_lock();
- if (__cgroup_freezing_or_frozen(tsk)) {
- rcu_read_unlock();
- return -EBUSY;
- }
- rcu_read_unlock();
- return 0;
+ return cgroup_freezing(tsk) ? -EBUSY : 0;
}
static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
@@ -279,7 +268,6 @@ static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
struct task_struct *task;
unsigned int num_cant_freeze_now = 0;
- freezer->state = CGROUP_FREEZING;
cgroup_iter_start(cgroup, &it);
while ((task = cgroup_iter_next(cgroup, &it))) {
if (!freeze_task(task, true))
@@ -303,8 +291,6 @@ static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
while ((task = cgroup_iter_next(cgroup, &it)))
__thaw_task(task);
cgroup_iter_end(cgroup, &it);
-
- freezer->state = CGROUP_THAWED;
}
static int freezer_change_state(struct cgroup *cgroup,
@@ -321,6 +307,8 @@ static int freezer_change_state(struct cgroup *cgroup,
if (goal_state == freezer->state)
goto out;
+ freezer->state = goal_state;
+
switch (goal_state) {
case CGROUP_THAWED:
unfreeze_cgroup(cgroup, freezer);
diff --git a/kernel/power/process.c b/kernel/power/process.c
index f8012f2..1bbc363 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -154,7 +154,7 @@ void thaw_processes(void)
read_lock(&tasklist_lock);
do_each_thread(g, p) {
- if (cgroup_freezing_or_frozen(p))
+ if (cgroup_freezing(p))
continue;
__thaw_task(p);
--
1.7.6
--
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