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rcu: decrease rcu_report_exp_rnp coupling with scheduler
PREEMPT_RCU read-side critical sections blocking an expedited grace period invoke rcu_report_exp_rnp(). When the last such critical section has completed, rcu_report_exp_rnp() invokes the scheduler to wake up the task that invoked synchronize_rcu_expedited() -- needlessly holding the root rcu_node structure's lock while doing so, thus needlessly providing a way for RCU and the scheduler to deadlock. This commit therefore releases the root rcu_node structure's lock before calling wake_up(). Reported-by: Ed Tomlinson <edt@aei.ca> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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@ -695,9 +695,12 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
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raw_spin_lock_irqsave(&rnp->lock, flags);
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raw_spin_lock_irqsave(&rnp->lock, flags);
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for (;;) {
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for (;;) {
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if (!sync_rcu_preempt_exp_done(rnp))
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if (!sync_rcu_preempt_exp_done(rnp)) {
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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break;
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break;
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}
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if (rnp->parent == NULL) {
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if (rnp->parent == NULL) {
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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wake_up(&sync_rcu_preempt_exp_wq);
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wake_up(&sync_rcu_preempt_exp_wq);
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break;
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break;
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}
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}
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@ -707,7 +710,6 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
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raw_spin_lock(&rnp->lock); /* irqs already disabled */
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raw_spin_lock(&rnp->lock); /* irqs already disabled */
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rnp->expmask &= ~mask;
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rnp->expmask &= ~mask;
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}
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}
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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}
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}
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/*
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/*
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