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container freezer: prevent frozen tasks or cgroups from changing

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Don't let frozen tasks or cgroups change.  This means frozen tasks can't
leave their current cgroup for another cgroup.  It also means that tasks
cannot be added to or removed from a cgroup in the FROZEN state.  We
enforce these rules by checking for frozen tasks and cgroups in the
can_attach() function.

Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matt Helsley 2008-10-18 20:27:22 -07:00 committed by Linus Torvalds
parent 5a06915c6d
commit 957a4eeaf4
1 changed files with 26 additions and 17 deletions
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43
kernel/cgroup_freezer.c
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@ -145,22 +145,40 @@ 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
* can_attach() result will remain valid until the attach completes.
*/
static int freezer_can_attach(struct cgroup_subsys *ss,
struct cgroup *new_cgroup,
struct task_struct *task)
{
struct freezer *freezer;
int retval = 0;
int retval;
/* Anything frozen can't move or be moved to/from */
if (is_task_frozen_enough(task))
return -EBUSY;
/*
* The call to cgroup_lock() in the freezer.state write method prevents
* a write to that file racing against an attach, and hence the
* can_attach() result will remain valid until the attach completes.
*/
freezer = cgroup_freezer(new_cgroup);
if (freezer->state == STATE_FROZEN)
return -EBUSY;
retval = 0;
task_lock(task);
freezer = task_freezer(task);
if (freezer->state == STATE_FROZEN)
retval = -EBUSY;
task_unlock(task);
return retval;
}
@ -193,12 +211,7 @@ static void check_if_frozen(struct cgroup *cgroup,
cgroup_iter_start(cgroup, &it);
while ((task = cgroup_iter_next(cgroup, &it))) {
ntotal++;
/*
* Task is frozen or will freeze immediately when next it gets
* woken
*/
if (frozen(task) ||
(task_is_stopped_or_traced(task) && freezing(task)))
if (is_task_frozen_enough(task))
nfrozen++;
}
@ -249,11 +262,7 @@ 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 (task_is_stopped_or_traced(task) && freezing(task))
/*
* The freeze flag is set so these tasks will
* immediately go into the fridge upon waking.
*/
if (is_task_frozen_enough(task))
continue;
if (!freezing(task) && !freezer_should_skip(task))
num_cant_freeze_now++;