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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-07-01 12:22:23 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-09-07 16:27:21 -0700
commit53c6d4edf874d3cbc031a53738c6cba9277faea5 (patch)
tree0f0fc1c5ade60c7243c7d5756694d21a9cc0df8a /kernel/rcu/update.c
parentbde6c3aa993066acb0d6ce32ecabe03b9d5df92d (diff)
downloadlinux-sh-53c6d4edf874d3cbc031a53738c6cba9277faea5.tar.gz
rcu: Add synchronous grace-period waiting for RCU-tasks
It turns out to be easier to add the synchronous grace-period waiting functions to RCU-tasks than to work around their absense in rcutorture, so this commit adds them. The key point is that the existence of call_rcu_tasks() means that rcutorture needs an rcu_barrier_tasks(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu/update.c')
-rw-r--r--kernel/rcu/update.c55
1 files changed, 55 insertions, 0 deletions
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 19b3dacb0753..5fd1ddbfcc55 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -381,6 +381,61 @@ void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp))
}
EXPORT_SYMBOL_GPL(call_rcu_tasks);
+/**
+ * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full rcu-tasks
+ * grace period has elapsed, in other words after all currently
+ * executing rcu-tasks read-side critical sections have elapsed. These
+ * read-side critical sections are delimited by calls to schedule(),
+ * cond_resched_rcu_qs(), idle execution, userspace execution, calls
+ * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
+ *
+ * This is a very specialized primitive, intended only for a few uses in
+ * tracing and other situations requiring manipulation of function
+ * preambles and profiling hooks. The synchronize_rcu_tasks() function
+ * is not (yet) intended for heavy use from multiple CPUs.
+ *
+ * Note that this guarantee implies further memory-ordering guarantees.
+ * On systems with more than one CPU, when synchronize_rcu_tasks() returns,
+ * each CPU is guaranteed to have executed a full memory barrier since the
+ * end of its last RCU-tasks read-side critical section whose beginning
+ * preceded the call to synchronize_rcu_tasks(). In addition, each CPU
+ * having an RCU-tasks read-side critical section that extends beyond
+ * the return from synchronize_rcu_tasks() is guaranteed to have executed
+ * a full memory barrier after the beginning of synchronize_rcu_tasks()
+ * and before the beginning of that RCU-tasks read-side critical section.
+ * Note that these guarantees include CPUs that are offline, idle, or
+ * executing in user mode, as well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned
+ * to its caller on CPU B, then both CPU A and CPU B are guaranteed
+ * to have executed a full memory barrier during the execution of
+ * synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU
+ * (but again only if the system has more than one CPU).
+ */
+void synchronize_rcu_tasks(void)
+{
+ /* Complain if the scheduler has not started. */
+ rcu_lockdep_assert(!rcu_scheduler_active,
+ "synchronize_rcu_tasks called too soon");
+
+ /* Wait for the grace period. */
+ wait_rcu_gp(call_rcu_tasks);
+}
+
+/**
+ * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
+ *
+ * Although the current implementation is guaranteed to wait, it is not
+ * obligated to, for example, if there are no pending callbacks.
+ */
+void rcu_barrier_tasks(void)
+{
+ /* There is only one callback queue, so this is easy. ;-) */
+ synchronize_rcu_tasks();
+}
+
/* See if the current task has stopped holding out, remove from list if so. */
static void check_holdout_task(struct task_struct *t)
{