From 3df494a32b936aef76d893f5065f962ebd9b9437 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Wed, 13 Dec 2006 00:34:28 -0800 Subject: [PATCH] [PATCH] PM: Fix freezing of stopped tasks Currently, if a task is stopped (ie. it's in the TASK_STOPPED state), it is considered by the freezer as unfreezeable. However, there may be a race between the freezer and the delivery of the continuation signal to the task resulting in the task running after we have finished freezing the other tasks. This, in turn, may lead to undesirable effects up to and including data corruption. To prevent this from happening we first need to make the freezer consider stopped tasks as freezeable. For this purpose we need to make freezeable() stop returning 0 for these tasks and we need to force them to enter the refrigerator. However, if there's no continuation signal in the meantime, the stopped tasks should remain stopped after all processes have been thawed, so we need to send an additional SIGSTOP to each of them before waking it up. Also, a stopped task that has just been woken up should first check if there's a freezing request for it and go to the refrigerator if that's the case. Signed-off-by: Rafael J. Wysocki Acked-by: Pavel Machek Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/power/process.c | 12 ++++++------ kernel/signal.c | 4 +++- 2 files changed, 9 insertions(+), 7 deletions(-) diff --git a/kernel/power/process.c b/kernel/power/process.c index 99eeb119b06d..b9a32860bef3 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -28,8 +28,7 @@ static inline int freezeable(struct task_struct * p) if ((p == current) || (p->flags & PF_NOFREEZE) || (p->exit_state == EXIT_ZOMBIE) || - (p->exit_state == EXIT_DEAD) || - (p->state == TASK_STOPPED)) + (p->exit_state == EXIT_DEAD)) return 0; return 1; } @@ -61,9 +60,12 @@ static inline void freeze_process(struct task_struct *p) unsigned long flags; if (!freezing(p)) { + if (p->state == TASK_STOPPED) + force_sig_specific(SIGSTOP, p); + freeze(p); spin_lock_irqsave(&p->sighand->siglock, flags); - signal_wake_up(p, 0); + signal_wake_up(p, p->state == TASK_STOPPED); spin_unlock_irqrestore(&p->sighand->siglock, flags); } } @@ -103,9 +105,7 @@ static unsigned int try_to_freeze_tasks(int freeze_user_space) if (frozen(p)) continue; - if (p->state == TASK_TRACED && - (frozen(p->parent) || - p->parent->state == TASK_STOPPED)) { + if (p->state == TASK_TRACED && frozen(p->parent)) { cancel_freezing(p); continue; } diff --git a/kernel/signal.c b/kernel/signal.c index 1921ffdc5e77..5630255d2e2a 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1705,7 +1705,9 @@ finish_stop(int stop_count) read_unlock(&tasklist_lock); } - schedule(); + do { + schedule(); + } while (try_to_freeze()); /* * Now we don't run again until continued. */