[PATCH 5.10.y 13/15] timers: Update the documentation to reflect on the new timer_shutdown() API

Jeongjun Park
2026-02-19T17:14:11Z

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>
---
Documentation/RCU/Design/Requirements/Requirements.rst | 2 +-
Documentation/core-api/local_ops.rst | 2 +-
Documentation/kernel-hacking/locking.rst | 5 +++++
3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index ad2cc20131ec..e8af3dc3c95a 100644
--- 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 unloaded, any attempt to call
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
diff --git a/Documentation/core-api/local_ops.rst b/Documentation/core-api/local_ops.rst
index a84f8b0c7ab2..0b42ceaaf3c4 100644
--- 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 a basic per cpu counter using

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

module_init(test_init);
diff --git a/Documentation/kernel-hacking/locking.rst b/Documentation/kernel-hacking/locking.rst
index 86ac2f4d24f7..4b8fd764aa7f 100644
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -1016,6 +1016,11 @@ calling add_timer() at the end of their timer function).
Because this is a fairly common case which is prone to races, you should
use timer_delete_sync() (``include/linux/timer.h``) to handle this case.

+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
=============

--