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From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
	jiangshanlai@gmail.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	"Paul E. McKenney" <paulmck@linux.ibm.com>
Subject: [PATCH tip/core/rcu 06/12] rcu: Make CPU-hotplug removal operations enable tick
Date: Wed,  2 Oct 2019 18:38:57 -0700	[thread overview]
Message-ID: <20191003013903.13079-6-paulmck@kernel.org> (raw)
In-Reply-To: <20191003013834.GA12927@paulmck-ThinkPad-P72>

From: "Paul E. McKenney" <paulmck@linux.ibm.com>

CPU-hotplug removal operations run the multi_cpu_stop() function, which
relies on the scheduler to gain control from whatever is running on the
various online CPUs, including any nohz_full CPUs running long loops in
kernel-mode code.  Lack of the scheduler-clock interrupt on such CPUs
can delay multi_cpu_stop() for several minutes and can also result in
RCU CPU stall warnings.  This commit therefore causes CPU-hotplug removal
operations to enable the scheduler-clock interrupt on all online CPUs.

[ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 kernel/rcu/tree.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f708d54..74bf5c65 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2091,6 +2091,7 @@ static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
  */
 int rcutree_dead_cpu(unsigned int cpu)
 {
+	int c;
 	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
 
@@ -2101,6 +2102,10 @@ int rcutree_dead_cpu(unsigned int cpu)
 	rcu_boost_kthread_setaffinity(rnp, -1);
 	/* Do any needed no-CB deferred wakeups from this CPU. */
 	do_nocb_deferred_wakeup(per_cpu_ptr(&rcu_data, cpu));
+
+	// Stop-machine done, so allow nohz_full to disable tick.
+	for_each_online_cpu(c)
+		tick_dep_clear_cpu(c, TICK_DEP_BIT_RCU);
 	return 0;
 }
 
@@ -3074,6 +3079,7 @@ static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
  */
 int rcutree_online_cpu(unsigned int cpu)
 {
+	int c;
 	unsigned long flags;
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
@@ -3087,6 +3093,10 @@ int rcutree_online_cpu(unsigned int cpu)
 		return 0; /* Too early in boot for scheduler work. */
 	sync_sched_exp_online_cleanup(cpu);
 	rcutree_affinity_setting(cpu, -1);
+
+	// Stop-machine done, so allow nohz_full to disable tick.
+	for_each_online_cpu(c)
+		tick_dep_clear_cpu(c, TICK_DEP_BIT_RCU);
 	return 0;
 }
 
@@ -3096,6 +3106,7 @@ int rcutree_online_cpu(unsigned int cpu)
  */
 int rcutree_offline_cpu(unsigned int cpu)
 {
+	int c;
 	unsigned long flags;
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
@@ -3107,6 +3118,10 @@ int rcutree_offline_cpu(unsigned int cpu)
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 
 	rcutree_affinity_setting(cpu, cpu);
+
+	// nohz_full CPUs need the tick for stop-machine to work quickly
+	for_each_online_cpu(c)
+		tick_dep_set_cpu(c, TICK_DEP_BIT_RCU);
 	return 0;
 }
 
-- 
2.9.5


  parent reply	other threads:[~2019-10-03  1:39 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-03  1:38 [PATCH tip/core/rcu 0/12] NO_HZ fixes for v5.5 Paul E. McKenney
2019-10-03  1:38 ` [PATCH tip/core/rcu 01/12] nohz: Add TICK_DEP_BIT_RCU paulmck
2019-10-03  1:38 ` [PATCH tip/core/rcu 02/12] time: Export tick start/stop functions for rcutorture paulmck
2019-10-03  1:38 ` [PATCH tip/core/rcu 03/12] rcu: Force on tick when invoking lots of callbacks paulmck
2019-10-03 14:10   ` Frederic Weisbecker
2019-10-05 16:42     ` Paul E. McKenney
2019-10-03  1:38 ` [PATCH tip/core/rcu 04/12] rcutorture: Force on tick for readers and callback flooders paulmck
2019-10-03 14:14   ` Frederic Weisbecker
2019-10-05 16:52     ` Paul E. McKenney
2019-10-03  1:38 ` [PATCH tip/core/rcu 05/12] stop_machine: EXP Provide RCU quiescent state in multi_cpu_stop() paulmck
2019-10-03  1:38 ` paulmck [this message]
2019-10-03 14:34   ` [PATCH tip/core/rcu 06/12] rcu: Make CPU-hotplug removal operations enable tick Frederic Weisbecker
2019-10-05 17:17     ` Paul E. McKenney
2019-10-03  1:38 ` [PATCH tip/core/rcu 07/12] stop_machine: Use {READ,WRITE)_ONCE() for multi_cpu_stop() ->state paulmck
2019-10-03  1:38 ` [PATCH tip/core/rcu 08/12] rcu: Force tick on for nohz_full CPUs not reaching quiescent states paulmck
2019-10-03 14:50   ` Frederic Weisbecker
2019-10-05 17:21     ` Paul E. McKenney
2019-10-03  1:39 ` [PATCH tip/core/rcu 09/12] rcu: Force nohz_full tick on upon irq enter instead of exit paulmck
2019-10-03  1:39 ` [PATCH tip/core/rcu 10/12] rcu: Reset CPU hints when reporting a quiescent state paulmck
2019-10-03  1:39 ` [PATCH tip/core/rcu 11/12] rcu: Confine ->core_needs_qs accesses to the corresponding CPU paulmck
2019-10-03  1:39 ` [PATCH tip/core/rcu 12/12] rcu: Make kernel-mode nohz_full CPUs invoke the RCU core processing paulmck

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