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Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler fix from Thomas Gleixner: "Fix a long standing state race in finish_task_switch()" * 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: sched/core: Fix TASK_DEAD race in finish_task_switch()
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@ -2517,11 +2517,11 @@ static struct rq *finish_task_switch(struct task_struct *prev)
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* If a task dies, then it sets TASK_DEAD in tsk->state and calls
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* schedule one last time. The schedule call will never return, and
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* the scheduled task must drop that reference.
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* The test for TASK_DEAD must occur while the runqueue locks are
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* still held, otherwise prev could be scheduled on another cpu, die
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* there before we look at prev->state, and then the reference would
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* be dropped twice.
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* Manfred Spraul <manfred@colorfullife.com>
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*
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* We must observe prev->state before clearing prev->on_cpu (in
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* finish_lock_switch), otherwise a concurrent wakeup can get prev
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* running on another CPU and we could rave with its RUNNING -> DEAD
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* transition, resulting in a double drop.
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*/
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prev_state = prev->state;
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vtime_task_switch(prev);
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@ -1078,9 +1078,10 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
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* After ->on_cpu is cleared, the task can be moved to a different CPU.
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* We must ensure this doesn't happen until the switch is completely
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* finished.
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*
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* Pairs with the control dependency and rmb in try_to_wake_up().
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*/
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smp_wmb();
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prev->on_cpu = 0;
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smp_store_release(&prev->on_cpu, 0);
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#endif
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#ifdef CONFIG_DEBUG_SPINLOCK
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/* this is a valid case when another task releases the spinlock */
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