freezer: add missing mb's to freezer_count() and freezer_should_skip()
A task is considered frozen enough between freezer_do_not_count() and freezer_count() and freezers use freezer_should_skip() to test this condition. This supposedly works because freezer_count() always calls try_to_freezer() after clearing %PF_FREEZER_SKIP. However, there currently is nothing which guarantees that freezer_count() sees %true freezing() after clearing %PF_FREEZER_SKIP when freezing is in progress, and vice-versa. A task can escape the freezing condition in effect by freezer_count() seeing !freezing() and freezer_should_skip() seeing %PF_FREEZER_SKIP. This patch adds smp_mb()'s to freezer_count() and freezer_should_skip() such that either %true freezing() is visible to freezer_count() or !PF_FREEZER_SKIP is visible to freezer_should_skip(). Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Rafael J. Wysocki <rjw@sisk.pl> Cc: stable@vger.kernel.orgwifi-calibration
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@ -75,28 +75,62 @@ static inline bool cgroup_freezing(struct task_struct *task)
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*/
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*/
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/* Tell the freezer not to count the current task as freezable. */
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/**
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* freezer_do_not_count - tell freezer to ignore %current
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*
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* Tell freezers to ignore the current task when determining whether the
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* target frozen state is reached. IOW, the current task will be
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* considered frozen enough by freezers.
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*
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* The caller shouldn't do anything which isn't allowed for a frozen task
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* until freezer_cont() is called. Usually, freezer[_do_not]_count() pair
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* wrap a scheduling operation and nothing much else.
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*/
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static inline void freezer_do_not_count(void)
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static inline void freezer_do_not_count(void)
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{
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{
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current->flags |= PF_FREEZER_SKIP;
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current->flags |= PF_FREEZER_SKIP;
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}
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}
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/*
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/**
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* Tell the freezer to count the current task as freezable again and try to
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* freezer_count - tell freezer to stop ignoring %current
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* freeze it.
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*
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* Undo freezer_do_not_count(). It tells freezers that %current should be
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* considered again and tries to freeze if freezing condition is already in
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* effect.
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*/
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*/
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static inline void freezer_count(void)
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static inline void freezer_count(void)
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{
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{
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current->flags &= ~PF_FREEZER_SKIP;
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current->flags &= ~PF_FREEZER_SKIP;
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/*
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* If freezing is in progress, the following paired with smp_mb()
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* in freezer_should_skip() ensures that either we see %true
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* freezing() or freezer_should_skip() sees !PF_FREEZER_SKIP.
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*/
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smp_mb();
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try_to_freeze();
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try_to_freeze();
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}
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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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* freezer_should_skip - whether to skip a task when determining frozen
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* state is reached
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* @p: task in quesion
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*
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* This function is used by freezers after establishing %true freezing() to
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* test whether a task should be skipped when determining the target frozen
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* state is reached. IOW, if this function returns %true, @p is considered
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* frozen enough.
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*/
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*/
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static inline int freezer_should_skip(struct task_struct *p)
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static inline bool freezer_should_skip(struct task_struct *p)
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{
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{
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return !!(p->flags & PF_FREEZER_SKIP);
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/*
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* The following smp_mb() paired with the one in freezer_count()
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* ensures that either freezer_count() sees %true freezing() or we
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* see cleared %PF_FREEZER_SKIP and return %false. This makes it
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* impossible for a task to slip frozen state testing after
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* clearing %PF_FREEZER_SKIP.
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*/
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smp_mb();
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return p->flags & PF_FREEZER_SKIP;
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}
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}
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/*
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/*
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