[PATCH v2] fs: Improve eventpoll logging to stop indicting timerfd

[Manish Varma <varmam@google.com>]

timerfd doesn't create any wakelocks, but eventpoll can.  When it does,
it names them after the underlying file descriptor, and since all
timerfd file descriptors are named "[timerfd]" (which saves memory on
systems like desktops with potentially many timerfd instances), all
wakesources created as a result of using the eventpoll-on-timerfd idiom
are called... "[timerfd]".

However, it becomes impossible to tell which "[timerfd]" wakesource is
affliated with which process and hence troubleshooting is difficult.

This change addresses this problem by changing the way eventpoll
wakesources are named:

1) the top-level per-process eventpoll wakesource is now named "epoll:P"
(instead of just "eventpoll"), where P, is the PID of the creating
process.
2) individual per-underlying-filedescriptor eventpoll wakesources are
now named "epollitemN:P.F", where N is a unique ID token and P is PID
of the creating process and F is the name of the underlying file
descriptor.

All together that should be splitted up into a change to eventpoll and
timerfd (or other file descriptors).

Co-developed-by: Kelly Rossmoyer <krossmo@google.com>
Signed-off-by: Kelly Rossmoyer <krossmo@google.com>
Signed-off-by: Manish Varma <varmam@google.com>
---
 fs/eventpoll.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 7df8c0fa462b..8d3369a02633 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -297,6 +297,7 @@ static LIST_HEAD(tfile_check_list);
 
 static long long_zero;
 static long long_max = LONG_MAX;
+static atomic_t wakesource_create_id  = ATOMIC_INIT(0);
 
 struct ctl_table epoll_table[] = {
 	{
@@ -1451,15 +1452,23 @@ static int ep_create_wakeup_source(struct epitem *epi)
 {
 	struct name_snapshot n;
 	struct wakeup_source *ws;
+	pid_t task_pid;
+	char buf[64];
+	int id;
+
+	task_pid = task_pid_nr(current);
 
 	if (!epi->ep->ws) {
-		epi->ep->ws = wakeup_source_register(NULL, "eventpoll");
+		snprintf(buf, sizeof(buf), "epoll:%d", task_pid);
+		epi->ep->ws = wakeup_source_register(NULL, buf);
 		if (!epi->ep->ws)
 			return -ENOMEM;
 	}
 
+	id = atomic_inc_return(&wakesource_create_id);
 	take_dentry_name_snapshot(&n, epi->ffd.file->f_path.dentry);
-	ws = wakeup_source_register(NULL, n.name.name);
+	snprintf(buf, sizeof(buf), "epollitem%d:%d.%s", id, task_pid, n.name.name);
+	ws = wakeup_source_register(NULL, buf);
 	release_dentry_name_snapshot(&n);
 
 	if (!ws)
-- 
2.31.0.291.g576ba9dcdaf-goog