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Commit 385b599e authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: Allow rcu_read_unlock_special() to raise_softirq() if in_irq() 



When running in an interrupt handler, raise_softirq() and
raise_softirq_irqoff() have extremely low overhead: They simply set a
bit in a per-CPU mask, which is checked upon exit from that interrupt
handler.  Therefore, if rcu_read_unlock_special() is invoked within an
interrupt handler and RCU_SOFTIRQ is in use, this commit make use of
raise_softirq_irqoff() even if there is no expedited grace period in
flight and even if this is not a nohz_full CPU.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 25102de6

kernel/rcu/tree_plugin.h

+1 −1
Original line number Diff line number Diff line
@@ -615,7 +615,7 @@ static void rcu_read_unlock_special(struct task_struct *t) 
		      (rdp->grpmask & rnp->expmask) ||

		      tick_nohz_full_cpu(rdp->cpu);

		// Need to defer quiescent state until everything is enabled.

		if (exp && irqs_were_disabled && use_softirq &&

		if ((exp || in_irq()) && irqs_were_disabled && use_softirq &&

		    (in_irq() || !t->rcu_read_unlock_special.b.deferred_qs)) {

			// Using softirq, safe to awaken, and we get

			// no help from enabling irqs, unlike bh/preempt.