[PATCH v5] fs: Improve eventpoll logging to stop indicting timerfd

[Isaac J. Manjarres]

From: Manish Varma <varmam@xxxxxxxxxx>

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
"epollN:P" (instead of just "eventpoll"), where N is a unique ID token,
and P is the PID of the creating process.
2) individual per-underlying-file descriptor 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.

Co-developed-by: Kelly Rossmoyer <krossmo@xxxxxxxxxx>
Signed-off-by: Kelly Rossmoyer <krossmo@xxxxxxxxxx>
Signed-off-by: Manish Varma <varmam@xxxxxxxxxx>
Co-developed-by: Isaac J. Manjarres <isaacmanjarres@xxxxxxxxxx>
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@xxxxxxxxxx>
---
 drivers/base/power/wakeup.c | 12 +++++++++---
 fs/eventpoll.c              | 11 +++++++++--
 include/linux/pm_wakeup.h   |  8 ++++----
 3 files changed, 22 insertions(+), 9 deletions(-)

 v1 -> v2:
 - Renamed instance count to wakesource_create_id to better describe
   its purpose.
 - Changed the wakeup source naming convention for wakeup sources
   created by eventpoll to avoid changing the timerfd names.
 - Used the PID of the process instead of the process name for the
   sake of uniqueness when creating wakeup sources.

v2 -> v3:
 - Changed wakeup_source_register() to take in a format string
   and arguments to avoid duplicating code to construct wakeup
   source names.
 - Moved the definition of wakesource_create_id so that it is
   always defined to fix an compilation error.

v3 -> v4:
 - Changed the naming convention for the top-level epoll wakeup
   sources to include an ID for uniqueness. This is needed in
   cases where a process is using two epoll fds.
 - Edited commit log to reflect new changes and add new tags.

v4 -> v5:
 - Added the format attribute to the wakeup_source_register()
   function to address a warning from the kernel test robot:
   https://lore.kernel.org/all/202406050504.UvdlPAQ0-lkp@xxxxxxxxx/

diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
index 752b417e8129..04a808607b62 100644
--- a/drivers/base/power/wakeup.c
+++ b/drivers/base/power/wakeup.c
@@ -209,13 +209,19 @@ EXPORT_SYMBOL_GPL(wakeup_source_remove);
 /**
  * wakeup_source_register - Create wakeup source and add it to the list.
  * @dev: Device this wakeup source is associated with (or NULL if virtual).
- * @name: Name of the wakeup source to register.
+ * @fmt: format string for the wakeup source name
  */
-struct wakeup_source *wakeup_source_register(struct device *dev,
-					     const char *name)
+__printf(2, 3) struct wakeup_source *wakeup_source_register(struct device *dev,
+							    const char *fmt, ...)
 {
 	struct wakeup_source *ws;
 	int ret;
+	char name[128];
+	va_list args;
+
+	va_start(args, fmt);
+	vsnprintf(name, sizeof(name), fmt, args);
+	va_end(args);
 
 	ws = wakeup_source_create(name);
 	if (ws) {
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index f53ca4f7fced..941df15208a4 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -338,6 +338,7 @@ static void __init epoll_sysctls_init(void)
 #define epoll_sysctls_init() do { } while (0)
 #endif /* CONFIG_SYSCTL */
 
+static atomic_t wakesource_create_id  = ATOMIC_INIT(0);
 static const struct file_operations eventpoll_fops;
 
 static inline int is_file_epoll(struct file *f)
@@ -1545,15 +1546,21 @@ static int ep_create_wakeup_source(struct epitem *epi)
 {
 	struct name_snapshot n;
 	struct wakeup_source *ws;
+	pid_t task_pid;
+	int id;
+
+	task_pid = task_pid_nr(current);
 
 	if (!epi->ep->ws) {
-		epi->ep->ws = wakeup_source_register(NULL, "eventpoll");
+		id = atomic_inc_return(&wakesource_create_id);
+		epi->ep->ws = wakeup_source_register(NULL, "epoll:%d:%d", id, task_pid);
 		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);
+	ws = wakeup_source_register(NULL, "epollitem%d:%d.%s", id, task_pid, n.name.name);
 	release_dentry_name_snapshot(&n);
 
 	if (!ws)
diff --git a/include/linux/pm_wakeup.h b/include/linux/pm_wakeup.h
index 76cd1f9f1365..1fb6dca981c2 100644
--- a/include/linux/pm_wakeup.h
+++ b/include/linux/pm_wakeup.h
@@ -99,8 +99,8 @@ extern struct wakeup_source *wakeup_source_create(const char *name);
 extern void wakeup_source_destroy(struct wakeup_source *ws);
 extern void wakeup_source_add(struct wakeup_source *ws);
 extern void wakeup_source_remove(struct wakeup_source *ws);
-extern struct wakeup_source *wakeup_source_register(struct device *dev,
-						    const char *name);
+extern __printf(2, 3) struct wakeup_source *wakeup_source_register(struct device *dev,
+								   const char *fmt, ...);
 extern void wakeup_source_unregister(struct wakeup_source *ws);
 extern int wakeup_sources_read_lock(void);
 extern void wakeup_sources_read_unlock(int idx);
@@ -140,8 +140,8 @@ static inline void wakeup_source_add(struct wakeup_source *ws) {}
 
 static inline void wakeup_source_remove(struct wakeup_source *ws) {}
 
-static inline struct wakeup_source *wakeup_source_register(struct device *dev,
-							   const char *name)
+static inline __printf(2, 3) struct wakeup_source *wakeup_source_register(struct device *dev,
+									  const char *fmt, ...)
 {
 	return NULL;
 }
-- 
2.45.2.505.gda0bf45e8d-goog