rcu: Fix attempt to avoid unsolicited offloading of callbacks

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@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
Tested-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d231aa17b1d7490092b1994facbe21c496bead66..cc7bed1c90dcffac2bb4c1cb18fe3748a76d3737 100644 (file)
--- 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/Kconfig b/init/Kconfig
index e84c6423a2e5a2dbe80157b13f8b16d17c3e2d06..64ee4d9677867b8949a0b38f3530c38c0eed3d9f 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -737,7 +737,7 @@ choice
 
 config RCU_NOCB_CPU_NONE
        bool "No build_forced no-CBs CPUs"
-       depends on RCU_NOCB_CPU && !NO_HZ_FULL_ALL
+       depends on RCU_NOCB_CPU
        help
          This option does not force any of the CPUs to be no-CBs CPUs.
          Only CPUs designated by the rcu_nocbs= boot parameter will be
@@ -751,7 +751,7 @@ config RCU_NOCB_CPU_NONE
 
 config RCU_NOCB_CPU_ZERO
        bool "CPU 0 is a build_forced no-CBs CPU"
-       depends on RCU_NOCB_CPU && !NO_HZ_FULL_ALL
+       depends on RCU_NOCB_CPU
        help
          This option forces CPU 0 to be a no-CBs CPU, so that its RCU
          callbacks are invoked by a per-CPU kthread whose name begins

diff --git a/init/main.c b/init/main.c
index bb1aed928f21391b63493112c6bb1a1eae39077f..e3c4cdd94d5b62ea561da64644e5e95708116ce1 100644 (file)
--- a/init/main.c
+++ b/init/main.c
@@ -578,6 +578,7 @@ 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 a7997e272564916d8ec2232b32867add334b6c77..06d077ccf8d5bd4141bfb07be95dfcab3068c182 100644 (file)
--- 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 +2424,67 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
        trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
 }
 
+void __init 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)
+       if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
+               need_rcu_nocb_mask = true;
+#endif /* #if defined(CONFIG_NO_HZ_FULL) */
+
+       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)
+       if (tick_nohz_full_running)
+               cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
+#endif /* #if defined(CONFIG_NO_HZ_FULL) */
+
+       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 +2513,6 @@ 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;