rcu: Make TASKS_RCU handle tasks that are almost done exiting

[karo-tx-linux.git] / kernel / rcu / update.c

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 5fd1ddbfcc55852d6b860b4edddea5b36226131d..403fc4ae539ed35d8ea5b8616f23319c33a0e339 100644 (file)
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -367,6 +367,13 @@ static struct rcu_head *rcu_tasks_cbs_head;
 static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
 static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
 
+/* Track exiting tasks in order to allow them to be waited for. */
+DEFINE_SRCU(tasks_rcu_exit_srcu);
+
+/* Control stall timeouts.  Disable with <= 0, otherwise jiffies till stall. */
+static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 3;
+module_param(rcu_task_stall_timeout, int, 0644);
+
 /* Post an RCU-tasks callback. */
 void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp))
 {
@@ -517,6 +524,15 @@ static int __noreturn rcu_tasks_kthread(void *arg)
                }
                rcu_read_unlock();
 
+               /*
+                * Wait for tasks that are in the process of exiting.
+                * This does only part of the job, ensuring that all
+                * tasks that were previously exiting reach the point
+                * where they have disabled preemption, allowing the
+                * later synchronize_sched() to finish the job.
+                */
+               synchronize_srcu(&tasks_rcu_exit_srcu);
+
                /*
                 * Each pass through the following loop scans the list
                 * of holdout tasks, removing any that are no longer
@@ -546,6 +562,11 @@ static int __noreturn rcu_tasks_kthread(void *arg)
                 * ->rcu_tasks_holdout accesses to be within the grace
                 * period, avoiding the need for memory barriers for
                 * ->rcu_tasks_holdout accesses.
+                *
+                * In addition, this synchronize_sched() waits for exiting
+                * tasks to complete their final preempt_disable() region
+                * of execution, cleaning up after the synchronize_srcu()
+                * above.
                 */
                synchronize_sched();