From f535a607c13c7b674e0788ca5765779aa74a01c3 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 22 Nov 2011 20:43:02 -0800 Subject: rcu: Eliminate RCU_FAST_NO_HZ grace-period hang With the new implementation of RCU_FAST_NO_HZ, it was possible to hang RCU grace periods as follows: o CPU 0 attempts to go idle, cycles several times through the rcu_prepare_for_idle() loop, then goes dyntick-idle when RCU needs nothing more from it, while still having at least on RCU callback pending. o CPU 1 goes idle with no callbacks. Both CPUs can then stay in dyntick-idle mode indefinitely, preventing the RCU grace period from ever completing, possibly hanging the system. This commit therefore prevents CPUs that have RCU callbacks from entering dyntick-idle mode. This approach also eliminates the need for the end-of-grace-period IPIs used previously. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 7fb8b0e6081..13fab4a9f9f 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1086,7 +1086,6 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) * callbacks are waiting on the grace period that just now * completed. */ - rcu_schedule_wake_gp_end(); if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ @@ -1672,7 +1671,6 @@ static void rcu_process_callbacks(struct softirq_action *unused) &__get_cpu_var(rcu_sched_data)); __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); rcu_preempt_process_callbacks(); - rcu_wake_cpus_for_gp_end(); trace_rcu_utilization("End RCU core"); } -- cgit v1.2.3-70-g09d2