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author | 2014-08-04 07:24:21 -0700 | |
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committer | 2014-09-07 16:27:29 -0700 | |
commit | 84a8f446ffd70c2799a96268aaa4d47c22a83ff0 (patch) | |
tree | 61e32afc24cfa6b7c33bcef6148851035b4149e6 /kernel/rcu/update.c | |
parent | documentation: Add verbiage on RCU-tasks stall warning messages (diff) | |
download | linux-84a8f446ffd70c2799a96268aaa4d47c22a83ff0.tar.gz linux-84a8f446ffd70c2799a96268aaa4d47c22a83ff0.tar.bz2 linux-84a8f446ffd70c2799a96268aaa4d47c22a83ff0.zip |
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.c | 33 |
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 */ |