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Date: Tue, 25 Jun 2024 19:58:43 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: "Isaac J. Manjarres" <isaacmanjarres@...gle.com>
Cc: tglx@...utronix.de, "Rafael J. Wysocki" <rafael@...nel.org>,
Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, saravanak@...gle.com,
Manish Varma <varmam@...gle.com>, Kelly Rossmoyer <krossmo@...gle.com>, kernel-team@...roid.com,
linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5] fs: Improve eventpoll logging to stop indicting
timerfd
On Thu, Jun 06, 2024 at 10:28:11AM -0700, Isaac J. Manjarres wrote:
> From: Manish Varma <varmam@...gle.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@...gle.com>
> Signed-off-by: Kelly Rossmoyer <krossmo@...gle.com>
> Signed-off-by: Manish Varma <varmam@...gle.com>
> Co-developed-by: Isaac J. Manjarres <isaacmanjarres@...gle.com>
> Signed-off-by: Isaac J. Manjarres <isaacmanjarres@...gle.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);
How often does this execute? Is it at most once per task lifespan?
The var probably wants to be annotated with ____cacheline_aligned_in_smp
so that it does not accidentally mess with other stuff.
I am assuming there is no constant traffic on it.
> 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
>
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