96ee6d8539
A kthread doing set_freezable*() may race with on-going PM freeze and the freezer might think all tasks are frozen while the new freezable kthread is merrily proceeding to execute code paths which aren't supposed to be executing during PM freeze. Reimplement set_freezable[_with_signal]() using __set_freezable() such that freezable PF flags are modified under freezer_lock and try_to_freeze() is called afterwards. This eliminates race condition against freezing. Note: Separated out from larger patch to resolve fix order dependency Oleg pointed out. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com>
199 lines
5.3 KiB
C
199 lines
5.3 KiB
C
/*
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* kernel/freezer.c - Function to freeze a process
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*
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* Originally from kernel/power/process.c
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*/
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#include <linux/interrupt.h>
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#include <linux/suspend.h>
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#include <linux/export.h>
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#include <linux/syscalls.h>
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#include <linux/freezer.h>
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#include <linux/kthread.h>
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/* total number of freezing conditions in effect */
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atomic_t system_freezing_cnt = ATOMIC_INIT(0);
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EXPORT_SYMBOL(system_freezing_cnt);
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/* indicate whether PM freezing is in effect, protected by pm_mutex */
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bool pm_freezing;
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bool pm_nosig_freezing;
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/* protects freezing and frozen transitions */
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static DEFINE_SPINLOCK(freezer_lock);
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/**
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* freezing_slow_path - slow path for testing whether a task needs to be frozen
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* @p: task to be tested
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*
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* This function is called by freezing() if system_freezing_cnt isn't zero
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* and tests whether @p needs to enter and stay in frozen state. Can be
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* called under any context. The freezers are responsible for ensuring the
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* target tasks see the updated state.
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*/
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bool freezing_slow_path(struct task_struct *p)
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{
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if (p->flags & PF_NOFREEZE)
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return false;
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if (pm_nosig_freezing || cgroup_freezing(p))
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return true;
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if (pm_freezing && !(p->flags & PF_FREEZER_NOSIG))
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return true;
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return false;
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}
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EXPORT_SYMBOL(freezing_slow_path);
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/* Refrigerator is place where frozen processes are stored :-). */
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bool __refrigerator(bool check_kthr_stop)
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{
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/* Hmm, should we be allowed to suspend when there are realtime
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processes around? */
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bool was_frozen = false;
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long save;
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/*
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* No point in checking freezing() again - the caller already did.
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* Proceed to enter FROZEN.
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*/
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spin_lock_irq(&freezer_lock);
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repeat:
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current->flags |= PF_FROZEN;
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spin_unlock_irq(&freezer_lock);
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save = current->state;
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pr_debug("%s entered refrigerator\n", current->comm);
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spin_lock_irq(¤t->sighand->siglock);
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recalc_sigpending(); /* We sent fake signal, clean it up */
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spin_unlock_irq(¤t->sighand->siglock);
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for (;;) {
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set_current_state(TASK_UNINTERRUPTIBLE);
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if (!freezing(current) ||
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(check_kthr_stop && kthread_should_stop()))
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break;
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was_frozen = true;
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schedule();
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}
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/* leave FROZEN */
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spin_lock_irq(&freezer_lock);
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if (freezing(current))
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goto repeat;
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current->flags &= ~PF_FROZEN;
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spin_unlock_irq(&freezer_lock);
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pr_debug("%s left refrigerator\n", current->comm);
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/*
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* Restore saved task state before returning. The mb'd version
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* needs to be used; otherwise, it might silently break
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* synchronization which depends on ordered task state change.
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*/
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set_current_state(save);
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return was_frozen;
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}
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EXPORT_SYMBOL(__refrigerator);
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static void fake_signal_wake_up(struct task_struct *p)
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{
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unsigned long flags;
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spin_lock_irqsave(&p->sighand->siglock, flags);
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signal_wake_up(p, 0);
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spin_unlock_irqrestore(&p->sighand->siglock, flags);
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}
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/**
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* freeze_task - send a freeze request to given task
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* @p: task to send the request to
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* @sig_only: if set, the request will only be sent if the task has the
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* PF_FREEZER_NOSIG flag unset
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* Return value: 'false', if @sig_only is set and the task has
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* PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
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*
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* The freeze request is sent by setting the tasks's TIF_FREEZE flag and
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* either sending a fake signal to it or waking it up, depending on whether
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* or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task
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* has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
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* TIF_FREEZE flag will not be set.
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*/
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bool freeze_task(struct task_struct *p, bool sig_only)
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{
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unsigned long flags;
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spin_lock_irqsave(&freezer_lock, flags);
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if (!freezing(p) || frozen(p)) {
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spin_unlock_irqrestore(&freezer_lock, flags);
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return false;
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}
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if (!(p->flags & PF_FREEZER_NOSIG)) {
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fake_signal_wake_up(p);
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/*
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* fake_signal_wake_up() goes through p's scheduler
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* lock and guarantees that TASK_STOPPED/TRACED ->
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* TASK_RUNNING transition can't race with task state
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* testing in try_to_freeze_tasks().
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*/
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} else {
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wake_up_state(p, TASK_INTERRUPTIBLE);
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}
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spin_unlock_irqrestore(&freezer_lock, flags);
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return true;
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}
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void __thaw_task(struct task_struct *p)
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{
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unsigned long flags;
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/*
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* Clear freezing and kick @p if FROZEN. Clearing is guaranteed to
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* be visible to @p as waking up implies wmb. Waking up inside
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* freezer_lock also prevents wakeups from leaking outside
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* refrigerator.
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*
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* If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
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* avoid leaving dangling TIF_SIGPENDING behind.
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*/
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spin_lock_irqsave(&freezer_lock, flags);
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if (frozen(p)) {
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wake_up_process(p);
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} else {
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spin_lock(&p->sighand->siglock);
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recalc_sigpending_and_wake(p);
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spin_unlock(&p->sighand->siglock);
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}
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spin_unlock_irqrestore(&freezer_lock, flags);
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}
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/**
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* __set_freezable - make %current freezable
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* @with_signal: do we want %TIF_SIGPENDING for notification too?
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*
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* Mark %current freezable and enter refrigerator if necessary.
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*/
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bool __set_freezable(bool with_signal)
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{
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might_sleep();
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/*
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* Modify flags while holding freezer_lock. This ensures the
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* freezer notices that we aren't frozen yet or the freezing
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* condition is visible to try_to_freeze() below.
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*/
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spin_lock_irq(&freezer_lock);
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current->flags &= ~PF_NOFREEZE;
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if (with_signal)
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current->flags &= ~PF_FREEZER_NOSIG;
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spin_unlock_irq(&freezer_lock);
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return try_to_freeze();
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}
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EXPORT_SYMBOL(__set_freezable);
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