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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-05-14 13:52:27 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-07-12 15:39:15 -0700
commit6f56f714db067056c80f5d71510118f82872e34c (patch)
tree831ac61392c65e088ed1ae8856b5f42de30fcd8d /kernel/rcu
parenta7538352da722fae5cc95ae6656ea2013f5b8b21 (diff)
rcu: Improve RCU-tasks naming and comments
The naming and comments associated with some RCU-tasks code make the faulty assumption that context switches due to cond_resched() are voluntary. As several people pointed out, this is not the case. This commit therefore updates function names and comments to better reflect current reality. Reported-by: Byungchul Park <byungchul.park@lge.com> Reported-by: Joel Fernandes <joel@joelfernandes.org> Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.c2
-rw-r--r--kernel/rcu/update.c27
2 files changed, 15 insertions, 14 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 6f2922168216..ccc061acf887 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -457,7 +457,7 @@ void rcu_note_context_switch(bool preempt)
rcu_momentary_dyntick_idle();
this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
if (!preempt)
- rcu_note_voluntary_context_switch_lite(current);
+ rcu_tasks_qs(current);
out:
trace_rcu_utilization(TPS("End context switch"));
barrier(); /* Avoid RCU read-side critical sections leaking up. */
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 4c230a60ece4..5783bdf86e5a 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -507,14 +507,15 @@ early_initcall(check_cpu_stall_init);
#ifdef CONFIG_TASKS_RCU
/*
- * Simple variant of RCU whose quiescent states are voluntary context switch,
- * user-space execution, and idle. As such, grace periods can take one good
- * long time. There are no read-side primitives similar to rcu_read_lock()
- * and rcu_read_unlock() because this implementation is intended to get
- * the system into a safe state for some of the manipulations involved in
- * tracing and the like. Finally, this implementation does not support
- * high call_rcu_tasks() rates from multiple CPUs. If this is required,
- * per-CPU callback lists will be needed.
+ * Simple variant of RCU whose quiescent states are voluntary context
+ * switch, cond_resched_rcu_qs(), user-space execution, and idle.
+ * As such, grace periods can take one good long time. There are no
+ * read-side primitives similar to rcu_read_lock() and rcu_read_unlock()
+ * because this implementation is intended to get the system into a safe
+ * state for some of the manipulations involved in tracing and the like.
+ * Finally, this implementation does not support high call_rcu_tasks()
+ * rates from multiple CPUs. If this is required, per-CPU callback lists
+ * will be needed.
*/
/* Global list of callbacks and associated lock. */
@@ -542,11 +543,11 @@ static struct task_struct *rcu_tasks_kthread_ptr;
* period elapses, in other words after all currently executing RCU
* read-side critical sections have completed. call_rcu_tasks() assumes
* that the read-side critical sections end at a voluntary context
- * switch (not a preemption!), entry into idle, or transition to usermode
- * execution. As such, there are no read-side primitives analogous to
- * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
- * to determine that all tasks have passed through a safe state, not so
- * much for data-strcuture synchronization.
+ * switch (not a preemption!), cond_resched_rcu_qs(), entry into idle,
+ * or transition to usermode execution. As such, there are no read-side
+ * primitives analogous to rcu_read_lock() and rcu_read_unlock() because
+ * this primitive is intended to determine that all tasks have passed
+ * through a safe state, not so much for data-strcuture synchronization.
*
* See the description of call_rcu() for more detailed information on
* memory ordering guarantees.