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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-08-04 07:24:21 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-09-07 16:27:29 -0700
commit84a8f446ffd70c2799a96268aaa4d47c22a83ff0 (patch)
tree61e32afc24cfa6b7c33bcef6148851035b4149e6 /kernel/rcu/update.c
parent37fe5f0e2713608573c5df5e529e13a135625629 (diff)
downloadlinux-sh-84a8f446ffd70c2799a96268aaa4d47c22a83ff0.tar.gz
rcu: Defer rcu_tasks_kthread() creation till first call_rcu_tasks()
It is expected that many sites will have CONFIG_TASKS_RCU=y, but will never actually invoke call_rcu_tasks(). For such sites, creating rcu_tasks_kthread() at boot is wasteful. This commit therefore defers creation of this kthread until the time of the first call_rcu_tasks(). This of course means that the first call_rcu_tasks() must be invoked from process context after the scheduler is fully operational. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu/update.c')
-rw-r--r--kernel/rcu/update.c33
1 files changed, 26 insertions, 7 deletions
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 444c8a303963..e1d71741958f 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -375,7 +375,12 @@ DEFINE_SRCU(tasks_rcu_exit_srcu);
static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;
module_param(rcu_task_stall_timeout, int, 0644);
-/* Post an RCU-tasks callback. */
+static void rcu_spawn_tasks_kthread(void);
+
+/*
+ * Post an RCU-tasks callback. First call must be from process context
+ * after the scheduler if fully operational.
+ */
void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp))
{
unsigned long flags;
@@ -388,8 +393,10 @@ void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp))
*rcu_tasks_cbs_tail = rhp;
rcu_tasks_cbs_tail = &rhp->next;
raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
- if (needwake)
+ if (needwake) {
+ rcu_spawn_tasks_kthread();
wake_up(&rcu_tasks_cbs_wq);
+ }
}
EXPORT_SYMBOL_GPL(call_rcu_tasks);
@@ -615,15 +622,27 @@ static int __noreturn rcu_tasks_kthread(void *arg)
}
}
-/* Spawn rcu_tasks_kthread() at boot time. */
-static int __init rcu_spawn_tasks_kthread(void)
+/* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */
+static void rcu_spawn_tasks_kthread(void)
{
- struct task_struct __maybe_unused *t;
+ static DEFINE_MUTEX(rcu_tasks_kthread_mutex);
+ static struct task_struct *rcu_tasks_kthread_ptr;
+ struct task_struct *t;
+ if (ACCESS_ONCE(rcu_tasks_kthread_ptr)) {
+ smp_mb(); /* Ensure caller sees full kthread. */
+ return;
+ }
+ mutex_lock(&rcu_tasks_kthread_mutex);
+ if (rcu_tasks_kthread_ptr) {
+ mutex_unlock(&rcu_tasks_kthread_mutex);
+ return;
+ }
t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
BUG_ON(IS_ERR(t));
- return 0;
+ smp_mb(); /* Ensure others see full kthread. */
+ ACCESS_ONCE(rcu_tasks_kthread_ptr) = t;
+ mutex_unlock(&rcu_tasks_kthread_mutex);
}
-early_initcall(rcu_spawn_tasks_kthread);
#endif /* #ifdef CONFIG_TASKS_RCU */