![Tejun Heo](/assets/img/avatar_default.png)
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>
193 lines
5.4 KiB
C++
193 lines
5.4 KiB
C++
/* Freezer declarations */
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#ifndef FREEZER_H_INCLUDED
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#define FREEZER_H_INCLUDED
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#include <linux/sched.h>
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#include <linux/wait.h>
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#include <linux/atomic.h>
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#ifdef CONFIG_FREEZER
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extern atomic_t system_freezing_cnt; /* nr of freezing conds in effect */
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extern bool pm_freezing; /* PM freezing in effect */
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extern bool pm_nosig_freezing; /* PM nosig freezing in effect */
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/*
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* Check if a process has been frozen
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*/
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static inline bool frozen(struct task_struct *p)
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{
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return p->flags & PF_FROZEN;
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}
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extern bool freezing_slow_path(struct task_struct *p);
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/*
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* Check if there is a request to freeze a process
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*/
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static inline bool freezing(struct task_struct *p)
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{
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if (likely(!atomic_read(&system_freezing_cnt)))
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return false;
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return freezing_slow_path(p);
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}
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/* Takes and releases task alloc lock using task_lock() */
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extern void __thaw_task(struct task_struct *t);
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extern bool __refrigerator(bool check_kthr_stop);
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extern int freeze_processes(void);
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extern int freeze_kernel_threads(void);
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extern void thaw_processes(void);
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static inline bool try_to_freeze(void)
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{
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might_sleep();
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if (likely(!freezing(current)))
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return false;
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return __refrigerator(false);
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}
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extern bool freeze_task(struct task_struct *p, bool sig_only);
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extern bool __set_freezable(bool with_signal);
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#ifdef CONFIG_CGROUP_FREEZER
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extern bool cgroup_freezing(struct task_struct *task);
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#else /* !CONFIG_CGROUP_FREEZER */
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static inline bool cgroup_freezing(struct task_struct *task)
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{
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return false;
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}
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#endif /* !CONFIG_CGROUP_FREEZER */
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/*
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* The PF_FREEZER_SKIP flag should be set by a vfork parent right before it
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* calls wait_for_completion(&vfork) and reset right after it returns from this
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* function. Next, the parent should call try_to_freeze() to freeze itself
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* appropriately in case the child has exited before the freezing of tasks is
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* complete. However, we don't want kernel threads to be frozen in unexpected
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* places, so we allow them to block freeze_processes() instead or to set
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* PF_NOFREEZE if needed and PF_FREEZER_SKIP is only set for userland vfork
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* parents. Fortunately, in the ____call_usermodehelper() case the parent won't
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* really block freeze_processes(), since ____call_usermodehelper() (the child)
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* does a little before exec/exit and it can't be frozen before waking up the
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* parent.
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*/
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/*
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* If the current task is a user space one, tell the freezer not to count it as
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* freezable.
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*/
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static inline void freezer_do_not_count(void)
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{
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if (current->mm)
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current->flags |= PF_FREEZER_SKIP;
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}
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/*
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* If the current task is a user space one, tell the freezer to count it as
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* freezable again and try to freeze it.
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*/
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static inline void freezer_count(void)
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{
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if (current->mm) {
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current->flags &= ~PF_FREEZER_SKIP;
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try_to_freeze();
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}
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}
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/*
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* Check if the task should be counted as freezable by the freezer
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*/
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static inline int freezer_should_skip(struct task_struct *p)
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{
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return !!(p->flags & PF_FREEZER_SKIP);
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}
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/*
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* Tell the freezer that the current task should be frozen by it
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*/
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static inline bool set_freezable(void)
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{
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return __set_freezable(false);
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}
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/*
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* Tell the freezer that the current task should be frozen by it and that it
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* should send a fake signal to the task to freeze it.
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*/
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static inline bool set_freezable_with_signal(void)
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{
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return __set_freezable(true);
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}
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/*
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* Freezer-friendly wrappers around wait_event_interruptible(),
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* wait_event_killable() and wait_event_interruptible_timeout(), originally
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* defined in <linux/wait.h>
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*/
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#define wait_event_freezekillable(wq, condition) \
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({ \
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int __retval; \
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freezer_do_not_count(); \
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__retval = wait_event_killable(wq, (condition)); \
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freezer_count(); \
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__retval; \
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})
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#define wait_event_freezable(wq, condition) \
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({ \
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int __retval; \
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do { \
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__retval = wait_event_interruptible(wq, \
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(condition) || freezing(current)); \
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if (__retval && !freezing(current)) \
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break; \
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else if (!(condition)) \
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__retval = -ERESTARTSYS; \
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} while (try_to_freeze()); \
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__retval; \
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})
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#define wait_event_freezable_timeout(wq, condition, timeout) \
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({ \
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long __retval = timeout; \
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do { \
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__retval = wait_event_interruptible_timeout(wq, \
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(condition) || freezing(current), \
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__retval); \
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} while (try_to_freeze()); \
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__retval; \
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})
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#else /* !CONFIG_FREEZER */
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static inline bool frozen(struct task_struct *p) { return false; }
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static inline bool freezing(struct task_struct *p) { return false; }
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static inline bool __refrigerator(bool check_kthr_stop) { return false; }
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static inline int freeze_processes(void) { return -ENOSYS; }
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static inline int freeze_kernel_threads(void) { return -ENOSYS; }
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static inline void thaw_processes(void) {}
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static inline bool try_to_freeze(void) { return false; }
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static inline void freezer_do_not_count(void) {}
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static inline void freezer_count(void) {}
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static inline int freezer_should_skip(struct task_struct *p) { return 0; }
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static inline void set_freezable(void) {}
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static inline void set_freezable_with_signal(void) {}
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#define wait_event_freezable(wq, condition) \
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wait_event_interruptible(wq, condition)
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#define wait_event_freezable_timeout(wq, condition, timeout) \
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wait_event_interruptible_timeout(wq, condition, timeout)
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#define wait_event_freezekillable(wq, condition) \
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wait_event_killable(wq, condition)
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#endif /* !CONFIG_FREEZER */
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#endif /* FREEZER_H_INCLUDED */
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