[PATCH v2] completion: Document that reinit_completion() must be called after complete_all()

Steven Rostedt
2017-08-16T17:12:06Z

The function complete_all() modifies the completion "done" variable to
UINT_MAX, and no other caller (wait_for_completion(), etc) will modify
it back to zero. That means that any call to complete_all() must have a
reinit_completion() before that completion can be used again.

Document this fact by the complete_all() function.

Also document that completion_done() will always return true if
complete_all() is called.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 13fc5ae..2950f44 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -47,6 +47,13 @@ EXPORT_SYMBOL(complete);
*
* It may be assumed that this function implies a write memory barrier before
* changing the task state if and only if any tasks are woken up.
+ *
+ * Since complete_all() sets the completion of @x permanently to done
+ * to allow multiple waiters to finish, a call to reinit_completion()
+ * must be used on @x if @x is to be used again. The code must make
+ * sure that all waiters have woken and finished before reinitializing
+ * @x. Also note that the function completion_done() can not be used
+ * to know if there are still waiters after complete_all() has been called.
*/
void complete_all(struct completion *x)
{
@@ -297,6 +304,7 @@ EXPORT_SYMBOL(try_wait_for_completion);
* Return: 0 if there are waiters (wait_for_completion() in progress)
* 1 if there are no waiters.
*
+ * Note, this will always return true if complete_all() was called on @X.
*/
bool completion_done(struct completion *x)
{