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

[Isaac Manjarres <isaacmanjarres@google.com>]

On Thu, Jun 06, 2024 at 10:28:11AM -0700, Isaac J. Manjarres wrote:
> 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 | 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@intel.com/
> 
> 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
Hello,

Just following up to see if there are comments or concerns with
this patch?

Thanks,
Isaac