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![Michal Hocko](/assets/img/avatar_default.png)
freezing_slow_path() is checking TIF_MEMDIE to skip OOM killed tasks. It is, however, checking the flag on the current task rather than the given one. This is really confusing because freezing() can be called also on !current tasks. It would end up working correctly for its main purpose because __refrigerator will be always called on the current task so the oom victim will never get frozen. But it could lead to surprising results when a task which is freezing a cgroup got oom killed because only part of the cgroup would get frozen. This is highly unlikely but worth fixing as the resulting code would be more clear anyway. Link: http://lkml.kernel.org/r/1467029719-17602-2-git-send-email-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: David Rientjes <rientjes@google.com> Cc: Miao Xie <miaox@cn.fujitsu.com> Cc: Miao Xie <miaoxie@huawei.com> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
179 lines
4.4 KiB
C
179 lines
4.4 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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/*
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* Temporary export for the deadlock workaround in ata_scsi_hotplug().
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* Remove once the hack becomes unnecessary.
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*/
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EXPORT_SYMBOL_GPL(pm_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 | PF_SUSPEND_TASK))
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return false;
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if (test_tsk_thread_flag(p, TIF_MEMDIE))
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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_KTHREAD))
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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 = current->state;
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pr_debug("%s entered refrigerator\n", current->comm);
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for (;;) {
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set_current_state(TASK_UNINTERRUPTIBLE);
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spin_lock_irq(&freezer_lock);
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current->flags |= PF_FROZEN;
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if (!freezing(current) ||
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(check_kthr_stop && kthread_should_stop()))
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current->flags &= ~PF_FROZEN;
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spin_unlock_irq(&freezer_lock);
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if (!(current->flags & PF_FROZEN))
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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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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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if (lock_task_sighand(p, &flags)) {
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signal_wake_up(p, 0);
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unlock_task_sighand(p, &flags);
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}
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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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*
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* If @p is freezing, the freeze request is sent either by sending a fake
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* signal (if it's not a kernel thread) or waking it up (if it's a kernel
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* thread).
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*
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* RETURNS:
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* %false, if @p is not freezing or already frozen; %true, otherwise
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*/
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bool freeze_task(struct task_struct *p)
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{
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unsigned long flags;
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/*
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* This check can race with freezer_do_not_count, but worst case that
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* will result in an extra wakeup being sent to the task. It does not
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* race with freezer_count(), the barriers in freezer_count() and
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* freezer_should_skip() ensure that either freezer_count() sees
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* freezing == true in try_to_freeze() and freezes, or
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* freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
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* normally.
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*/
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if (freezer_should_skip(p))
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return false;
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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_KTHREAD))
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fake_signal_wake_up(p);
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else
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wake_up_state(p, TASK_INTERRUPTIBLE);
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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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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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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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*
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* Mark %current freezable and enter refrigerator if necessary.
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*/
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bool set_freezable(void)
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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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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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