From 6907483b4e803a20f0b48cc9afa3817420ce61c5 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:24 -0800 Subject: [PATCH] freezer: make freezing indicate freeze condition in effect Currently freezing (TIF_FREEZE) and frozen (PF_FROZEN) states are interlocked - freezing is set to request freeze and when the task actually freezes, it clears freezing and sets frozen. This interlocking makes things more complex than necessary - freezing doesn't mean there's freezing condition in effect and frozen doesn't match the task actually entering and leaving frozen state (it's cleared by the thawing task). This patch makes freezing indicate that freeze condition is in effect. A task enters and stays frozen if freezing. This makes PF_FROZEN manipulation done only by the task itself and prevents wakeup from __thaw_task() leaking outside of refrigerator. The only place which needs to tell freezing && !frozen is try_to_freeze_task() to whine about tasks which don't enter frozen. It's updated to test the condition explicitly. With the change, frozen() state my linger after __thaw_task() until the task wakes up and exits fridge. This can trigger BUG_ON() in update_if_frozen(). Work it around by testing freezing() && frozen() instead of frozen(). -v2: Oleg pointed out missing re-check of freezing() when trying to clear FROZEN and possible spurious BUG_ON() trigger in update_if_frozen(). Both fixed. Signed-off-by: Tejun Heo Cc: Oleg Nesterov Cc: Paul Menage --- kernel/cgroup_freezer.c | 2 +- kernel/freezer.c | 42 +++++++++++++++++++++++------------------ kernel/power/process.c | 3 ++- 3 files changed, 27 insertions(+), 20 deletions(-) diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index a6d405a86ee0..cd27b0825560 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -231,7 +231,7 @@ 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 (freezing(task) && frozen(task)) nfrozen++; } diff --git a/kernel/freezer.c b/kernel/freezer.c index 4130e48649bb..a8822be43da0 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -22,14 +22,19 @@ bool __refrigerator(bool check_kthr_stop) bool was_frozen = false; long save; + /* + * Enter FROZEN. If NOFREEZE, schedule immediate thawing by + * clearing freezing. + */ spin_lock_irq(&freezer_lock); +repeat: if (!freezing(current)) { spin_unlock_irq(&freezer_lock); return was_frozen; } - if (!(current->flags & PF_NOFREEZE)) - current->flags |= PF_FROZEN; - clear_freeze_flag(current); + if (current->flags & PF_NOFREEZE) + clear_freeze_flag(current); + current->flags |= PF_FROZEN; spin_unlock_irq(&freezer_lock); save = current->state; @@ -44,7 +49,7 @@ bool __refrigerator(bool check_kthr_stop) for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); - if (!frozen(current) || + if (!freezing(current) || (check_kthr_stop && kthread_should_stop())) break; was_frozen = true; @@ -54,6 +59,13 @@ bool __refrigerator(bool check_kthr_stop) /* Remove the accounting blocker */ current->flags &= ~PF_FREEZING; + /* leave FROZEN */ + spin_lock_irq(&freezer_lock); + if (freezing(current)) + goto repeat; + current->flags &= ~PF_FROZEN; + spin_unlock_irq(&freezer_lock); + pr_debug("%s left refrigerator\n", current->comm); /* @@ -137,25 +149,19 @@ void cancel_freezing(struct task_struct *p) spin_unlock_irqrestore(&freezer_lock, flags); } -/* - * Wake up a frozen task - * - * task_lock() is needed to prevent the race with refrigerator() which may - * occur if the freezing of tasks fails. Namely, without the lock, if the - * freezing of tasks failed, thaw_tasks() might have run before a task in - * refrigerator() could call frozen_process(), in which case the task would be - * frozen and no one would thaw it. - */ void __thaw_task(struct task_struct *p) { unsigned long flags; + /* + * Clear freezing and kick @p if FROZEN. Clearing is guaranteed to + * be visible to @p as waking up implies wmb. Waking up inside + * freezer_lock also prevents wakeups from leaking outside + * refrigerator. + */ spin_lock_irqsave(&freezer_lock, flags); - if (frozen(p)) { - p->flags &= ~PF_FROZEN; + clear_freeze_flag(p); + if (frozen(p)) wake_up_process(p); - } else { - clear_freeze_flag(p); - } spin_unlock_irqrestore(&freezer_lock, flags); } diff --git a/kernel/power/process.c b/kernel/power/process.c index bd420ca48261..e6e2739190b5 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -118,7 +118,8 @@ static int try_to_freeze_tasks(bool sig_only) read_lock(&tasklist_lock); do_each_thread(g, p) { - if (!wakeup && freezing(p) && !freezer_should_skip(p)) + if (!wakeup && !freezer_should_skip(p) && + freezing(p) && !frozen(p)) sched_show_task(p); cancel_freezing(p); } while_each_thread(g, p); -- GitLab