Commit 131906b0 authored Jul 17, 2011 by Paul E. McKenney

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>

parent b0d30417

kernel/rcutree_plugin.h

+4 −2

Original line number	Diff line number	Diff line
		@@ -695,9 +695,12 @@ static void rcu_report_exp_rnp(struct rcu_state rsp, struct rcu_node rnp)

		raw_spin_lock_irqsave(&rnp->lock, flags);
		for (;;) {
		if (!sync_rcu_preempt_exp_done(rnp))
		if (!sync_rcu_preempt_exp_done(rnp)) {
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		break;
		}
		if (rnp->parent == NULL) {
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		wake_up(&sync_rcu_preempt_exp_wq);
		break;
		}
		@@ -707,7 +710,6 @@ static void rcu_report_exp_rnp(struct rcu_state rsp, struct rcu_node rnp)
		raw_spin_lock(&rnp->lock); /* irqs already disabled */
		rnp->expmask &= ~mask;
		}
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		}

		/*