From: Paul E. McKenney Date: Mon, 1 Apr 2019 22:12:47 +0000 (-0700) Subject: rcu: Allow rcu_read_unlock_special() to raise_softirq() if in_irq() X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=385b599e8c04fa843c4d7f785478827cc512d720;p=linux.git 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: Paul E. McKenney --- diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index d15cdab6aeb48..e1005f5e8094e 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -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.