[PATCH v4] fs: Improve eventpoll logging to stop indicting timerfd

Isaac J. Manjarres
2024-06-04T17:36:11Z

From: 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
"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@google.com>
Signed-off-by: Kelly Rossmoyer <krossmo@google.com>
Signed-off-by: Manish Varma <varmam@google.com>
Co-developed-by: Isaac J. Manjarres <isaacmanjarres@google.com>
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
---
drivers/base/power/wakeup.c | 10 ++++++++--
fs/eventpoll.c | 11 +++++++++--
include/linux/pm_wakeup.h | 4 ++--
3 files changed, 19 insertions(+), 6 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.

diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
index 752b417e8129..86276f904be8 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)
+ 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..40972ca262cc 100644
--- a/include/linux/pm_wakeup.h
+++ b/include/linux/pm_wakeup.h
@@ -100,7 +100,7 @@ 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);
+ 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);
@@ -141,7 +141,7 @@ 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)
+ const char *fmt, ...)
{
return NULL;
}
--
2.45.1.288.g0e0cd299f1-goog