From 33e1c288da62a6a5aa9077a6b7bfa690b1b02cf4 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Wed, 23 May 2007 13:57:24 -0700 Subject: [PATCH] freezer: close potential race between refrigerator and thaw_tasks If the freezing of tasks fails and a task is preempted in refrigerator() before calling frozen_process(), then thaw_tasks() may run before this task is frozen. In that case the task will freeze and no one will thaw it. To fix this race we can call freezing(current) in refrigerator() along with frozen_process(current) under the task_lock() which also should be taken in the error path of try_to_freeze_tasks() as well as in thaw_process(). Moreover, if thaw_process() additionally clears TIF_FREEZE for tasks that are not frozen, we can be sure that all tasks are thawed and there are no pending "freeze" requests after thaw_tasks() has run. Signed-off-by: Rafael J. Wysocki Acked-by: Pavel Machek Cc: Gautham R Shenoy Cc: Oleg Nesterov Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/freezer.h | 10 ++++++++++ kernel/power/process.c | 12 +++++++++++- 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index 5e75e26d4787..db5423eae24d 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -37,14 +37,24 @@ static inline void do_not_freeze(struct task_struct *p) /* * Wake up a frozen process + * + * task_lock() is taken 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. */ static inline int thaw_process(struct task_struct *p) { + task_lock(p); if (frozen(p)) { p->flags &= ~PF_FROZEN; + task_unlock(p); wake_up_process(p); return 1; } + clear_tsk_thread_flag(p, TIF_FREEZE); + task_unlock(p); return 0; } diff --git a/kernel/power/process.c b/kernel/power/process.c index 088419387388..02e490e311eb 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -37,10 +37,18 @@ void refrigerator(void) /* Hmm, should we be allowed to suspend when there are realtime processes around? */ long save; + + task_lock(current); + if (freezing(current)) { + frozen_process(current); + task_unlock(current); + } else { + task_unlock(current); + return; + } save = current->state; pr_debug("%s entered refrigerator\n", current->comm); - frozen_process(current); spin_lock_irq(¤t->sighand->siglock); recalc_sigpending(); /* We sent fake signal, clean it up */ spin_unlock_irq(¤t->sighand->siglock); @@ -152,10 +160,12 @@ static unsigned int try_to_freeze_tasks(int freeze_user_space) if (is_user_space(p) == !freeze_user_space) continue; + task_lock(p); if (freezeable(p) && !frozen(p)) printk(KERN_ERR " %s\n", p->comm); cancel_freezing(p); + task_unlock(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); }