From 6a949b7af82db7eb1e52caaed122eab1cf63acee Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 28 Jul 2019 11:50:56 -0700 Subject: [PATCH] rcu: Force on tick when invoking lots of callbacks Callback invocation can run for a significant time period, and within CONFIG_NO_HZ_FULL=y kernels, this period will be devoid of scheduler-clock interrupts. In-kernel execution without such interrupts can cause all manner of malfunction, with RCU CPU stall warnings being but one result. This commit therefore forces scheduling-clock interrupts on whenever more than a few RCU callbacks are invoked. Because offloaded callback invocation can be preempted, this forcing is withdrawn on each context switch. This in turn requires that the loop invoking RCU callbacks reiterate the forcing periodically. [ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ] [ paulmck: Remove NO_HZ_FULL check per Frederic Weisbecker feedback. ] Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 81105141b6a8..238f93b4b0a4 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2151,6 +2151,7 @@ static void rcu_do_batch(struct rcu_data *rdp) rcu_nocb_unlock_irqrestore(rdp, flags); /* Invoke callbacks. */ + tick_dep_set_task(current, TICK_DEP_BIT_RCU); rhp = rcu_cblist_dequeue(&rcl); for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) { debug_rcu_head_unqueue(rhp); @@ -2217,6 +2218,7 @@ static void rcu_do_batch(struct rcu_data *rdp) /* Re-invoke RCU core processing if there are callbacks remaining. */ if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist)) invoke_rcu_core(); + tick_dep_clear_task(current, TICK_DEP_BIT_RCU); } /*