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Message-ID: <20140725233623.GA18537@linux.vnet.ibm.com>
Date: Fri, 25 Jul 2014 16:36:23 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
bobby.prani@...il.com, sasha.levin@...cle.com
Subject: [PATCH RFC tip/core/rcu] Fix attempt to avoid offloading callbacks
unless requested
[ Note: This applies on top of commit 187497fa5e9e (rcu: Allow for NULL
tick_nohz_full_mask when nohz_full= missing) in -tip
or -rcu. To make this work on top of rcu/next, move the
call to rcu_organize_nocb_kthreads(rsp) to the end of the
for_each_rcu_flavor(rsp) loop in rcu_init_nohz(). ]
Commit b58cc46c5f6b (rcu: Don't offload callbacks unless specifically
requested) failed to adjust the callback lists of the CPUs that are
known to be no-CBs CPUs only because they are also nohz_full= CPUs.
This failure can result in callbacks that are posted during early boot
getting stranded on nxtlist for CPUs whose no-CBs property becomes
apparent late, and there can also be spurious warnings about offline
CPUs posting callbacks.
This commit fixes these problems by adding an early-boot rcu_init_nohz()
that properly initializes the no-CBs CPUs.
Note that kernels built with CONFIG_RCU_NOCB_CPU_ALL=y or with
CONFIG_RCU_NOCB_CPU=n do not exhibit this bug. Neither do kernels
booted without the nohz_full= boot parameter.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d231aa17b1d7..cc7bed1c90dc 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -269,6 +269,14 @@ static inline void rcu_user_hooks_switch(struct task_struct *prev,
struct task_struct *next) { }
#endif /* CONFIG_RCU_USER_QS */
+#ifdef CONFIG_RCU_NOCB_CPU
+void rcu_init_nohz(void);
+#else /* #ifdef CONFIG_RCU_NOCB_CPU */
+static inline void rcu_init_nohz(void)
+{
+}
+#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
+
/**
* RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
* @a: Code that RCU needs to pay attention to.
diff --git a/init/main.c b/init/main.c
index e8ae1fef0908..5d8c83ae6c55 100644
--- a/init/main.c
+++ b/init/main.c
@@ -577,6 +577,7 @@ asmlinkage __visible void __init start_kernel(void)
idr_init_cache();
rcu_init();
tick_nohz_init();
+ rcu_init_nohz();
context_tracking_init();
radix_tree_init();
/* init some links before init_ISA_irqs() */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 00dc411e9676..095d6e4d2fd7 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -85,33 +85,6 @@ static void __init rcu_bootup_announce_oddness(void)
pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
if (nr_cpu_ids != NR_CPUS)
pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
-#ifdef CONFIG_RCU_NOCB_CPU
-#ifndef CONFIG_RCU_NOCB_CPU_NONE
- if (!have_rcu_nocb_mask) {
- zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
- have_rcu_nocb_mask = true;
- }
-#ifdef CONFIG_RCU_NOCB_CPU_ZERO
- pr_info("\tOffload RCU callbacks from CPU 0\n");
- cpumask_set_cpu(0, rcu_nocb_mask);
-#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
-#ifdef CONFIG_RCU_NOCB_CPU_ALL
- pr_info("\tOffload RCU callbacks from all CPUs\n");
- cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
-#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
-#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
- if (have_rcu_nocb_mask) {
- if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
- pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
- cpumask_and(rcu_nocb_mask, cpu_possible_mask,
- rcu_nocb_mask);
- }
- cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
- pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
- if (rcu_nocb_poll)
- pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
- }
-#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
}
#ifdef CONFIG_TREE_PREEMPT_RCU
@@ -2451,6 +2424,66 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
}
+void rcu_init_nohz(void)
+{
+ int cpu;
+ bool need_rcu_nocb_mask = true;
+ struct rcu_state *rsp;
+
+#ifdef CONFIG_RCU_NOCB_CPU_NONE
+ need_rcu_nocb_mask = false;
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
+
+#if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL)
+ if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
+ need_rcu_nocb_mask = true;
+#endif /* #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL) */
+
+ if (!have_rcu_nocb_mask && need_rcu_nocb_mask) {
+ zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
+ have_rcu_nocb_mask = true;
+ }
+ if (!have_rcu_nocb_mask)
+ return;
+
+#ifdef CONFIG_RCU_NOCB_CPU_ZERO
+ pr_info("\tOffload RCU callbacks from CPU 0\n");
+ cpumask_set_cpu(0, rcu_nocb_mask);
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
+#ifdef CONFIG_RCU_NOCB_CPU_ALL
+ pr_info("\tOffload RCU callbacks from all CPUs\n");
+ cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
+#if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL)
+ cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
+#endif /* #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL) */
+
+ if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
+ pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
+ cpumask_and(rcu_nocb_mask, cpu_possible_mask,
+ rcu_nocb_mask);
+ }
+ cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
+ pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
+ if (rcu_nocb_poll)
+ pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
+
+ for_each_rcu_flavor(rsp) {
+ for_each_cpu(cpu, rcu_nocb_mask) {
+ struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+
+ /*
+ * If there are early callbacks, they will need
+ * to be moved to the nocb lists.
+ */
+ WARN_ON_ONCE(rdp->nxttail[RCU_NEXT_TAIL] !=
+ &rdp->nxtlist &&
+ rdp->nxttail[RCU_NEXT_TAIL] != NULL);
+ init_nocb_callback_list(rdp);
+ }
+ }
+}
+
/* Initialize per-rcu_data variables for no-CBs CPUs. */
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
@@ -2479,10 +2512,6 @@ static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
if (rcu_nocb_mask == NULL)
return;
-#if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL)
- if (tick_nohz_full_running)
- cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
-#endif /* #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL) */
if (ls == -1) {
ls = int_sqrt(nr_cpu_ids);
rcu_nocb_leader_stride = ls;
--
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