linux-kernel - [PATCH v6 6/6] timers: Update the documentation to reflect on the new timer

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Message-ID: <20221110064147.712934793@goodmis.org>
Date:   Thu, 10 Nov 2022 01:41:07 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Julia Lawall <Julia.Lawall@...ia.fr>
Subject: [PATCH v6 6/6] timers: Update the documentation to reflect on the new
 timer_shutdown() API

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

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.

Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Stephen Boyd <sboyd@...nel.org>
Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Julia Lawall <Julia.Lawall@...ia.fr>
Tested-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 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 a0f8164c8513..ec6de88846b9 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 del_timer_sync() or similar.
+with via timer_shutdown_sync().
 
 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 2ac3f9f29845..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)
     {
-            del_timer_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 6805ae6e86e6..eb341b69fd15 100644
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -1009,6 +1009,11 @@ use del_timer_sync() (``include/linux/timer.h``) to
 handle this case. It returns the number of times the timer had to be
 deleted before we finally stopped it from adding itself back in.
 
+Before freeing a timer, timer_shutdown() or timer_shutdown_sync() should be
+called which will keep it from being rearmed, although if it is rearmed, it
+will produce a warning.
+
+
 Locking Speed
 =============
 
-- 
2.35.1