[tip: timers/core] timers: Update the documentation to reflect on the new timer_shutdown() API

From: tip-bot2 for Steven Rostedt (Google)
Date: Thu Nov 24 2022 - 09:16:22 EST


The following commit has been merged into the timers/core branch of tip:

Commit-ID: a31323bef2b66455920d054b160c17d4240f8fd4
Gitweb: https://git.kernel.org/tip/a31323bef2b66455920d054b160c17d4240f8fd4
Author: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
AuthorDate: Wed, 23 Nov 2022 21:18:55 +01:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Thu, 24 Nov 2022 15:09:12 +01:00

timers: Update the documentation to reflect on the new timer_shutdown() API

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@xxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Reviewed-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
Reviewed-by: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20221110064147.712934793@xxxxxxxxxxx
Link: https://lore.kernel.org/r/20221123201625.375284489@xxxxxxxxxxxxx

---
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(-)

diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index 546f23a..49387d8 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 a84f8b0..0b42cea 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 c5b8678..c756786 100644
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -1007,6 +1007,11 @@ 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
=============

diff --git a/Documentation/translations/zh_CN/core-api/local_ops.rst b/Documentation/translations/zh_CN/core-api/local_ops.rst
index 22493b9..eb5423f 100644
--- a/Documentation/translations/zh_CN/core-api/local_ops.rst
+++ b/Documentation/translations/zh_CN/core-api/local_ops.rst
@@ -185,7 +185,7 @@ UP之间没有不同的行为,在你的架构的 ``local.h`` 中包括 ``asm-g

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

module_init(test_init);