[tip:sched/core] sched/completion: Document that reinit_completion() must be called after complete_all()

tip-bot for Steven Rostedt
2017-08-16T18:17:35Z

Commit-ID: 9c8783201cb58e9af8ddeb0cc68f37b0a44ca16c
Gitweb: http://git.kernel.org/tip/9c8783201cb58e9af8ddeb0cc68f37b0a44ca16c
Author: Steven Rostedt <rostedt@goodmis.org>
AuthorDate: Wed, 16 Aug 2017 13:12:02 -0400
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 16 Aug 2017 20:08:10 +0200

sched/completion: Document that reinit_completion() must be called after complete_all()

The complete_all() function modifies the completion's "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>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170816131202.195c2f4b@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/completion.c | 8 ++++++++
1 file changed, 8 insertions(+)

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)
{