From 957a4eeaf4af614ab0fc4c09a22593d6ab233f5b Mon Sep 17 00:00:00 2001 From: Matt Helsley Date: Sat, 18 Oct 2008 20:27:22 -0700 Subject: [PATCH] container freezer: prevent frozen tasks or cgroups from changing 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/cgroup_freezer.c | 43 +++++++++++++++++++++++++---------------- 1 file changed, 26 insertions(+), 17 deletions(-) diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index b08722de610..df884022fbd 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -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++; -- 2.20.1