[PATCH 5.15 20/75] timers: Update the documentation to reflect on the new timer_shutdown() API

Greg Kroah-Hartman
2026-02-09T14:53:26Z

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5.15-stable review patch. If anyone has any objections, please let me know.

------------------

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

[ Upstream commit a31323bef2b66455920d054b160c17d4240f8fd4 ]

In order to make sure that a timer is not re-armed after it is stopped
before freeing, a new shutdown state is added to the timer code. The API
timer_shutdown_sync() and timer_shutdown() must be called before the
object that holds the timer can be freed.

Update the documentation to reflect this new workflow.

[ tglx: Updated to the new semantics and updated the zh_CN version ]

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Link: https://lore.kernel.org/r/20221110064147.712934793@goodmis.org
Link: https://lore.kernel.org/r/20221123201625.375284489@linutronix.de
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Documentation/RCU/Design/Requirements/Requirements.rst | 2 +-
Documentation/core-api/local_ops.rst | 2 +-
Documentation/kernel-hacking/locking.rst | 5 +++++
Documentation/translations/zh_CN/core-api/local_ops.rst | 2 +-
4 files changed, 8 insertions(+), 3 deletions(-)

--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -1858,7 +1858,7 @@ unloaded. After a given module has been
one of its functions results in a segmentation fault. The module-unload
functions must therefore cancel any delayed calls to loadable-module
functions, for example, any outstanding mod_timer() must be dealt
-with via timer_delete_sync() or similar.
+with via timer_shutdown_sync() or similar.

Unfortunately, there is no way to cancel an RCU callback; once you
invoke call_rcu(), the callback function is eventually going to be
--- a/Documentation/core-api/local_ops.rst
+++ b/Documentation/core-api/local_ops.rst
@@ -191,7 +191,7 @@ Here is a sample module which implements

static void __exit test_exit(void)
{
- timer_delete_sync(&test_timer);
+ timer_shutdown_sync(&test_timer);
}

module_init(test_init);
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -1010,6 +1010,11 @@ calling add_timer() at the end of their
Because this is a fairly common case which is prone to races, you should
use timer_delete_sync() (``include/linux/timer.h``) to

+Before freeing a timer, timer_shutdown() or timer_shutdown_sync() should be
+called which will keep it from being rearmed. Any subsequent attempt to
+rearm the timer will be silently ignored by the core code.
+
+
Locking Speed
=============

--- a/Documentation/translations/zh_CN/core-api/local_ops.rst
+++ b/Documentation/translations/zh_CN/core-api/local_ops.rst
@@ -185,7 +185,7 @@ UPä¹‹é—´æ²¡æœ‰ä¸åŒçš„è¡Œä¸ºï¼Œåœ¨ä½ çš

static void __exit test_exit(void)
{
- timer_delete_sync(&test_timer);
+ timer_shutdown_sync(&test_timer);
}

module_init(test_init);