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rcu: Allow rcu_read_unlock_special() to raise_softirq() if in_irq()

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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: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-04-01 15:12:47 -07:00
parent 25102de65f
commit 385b599e8c
1 changed files with 1 additions and 1 deletions
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2
kernel/rcu/tree_plugin.h
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@ -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.