netdev - [patch 14/15] timers: Update the documentation to reflect on the new timer

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Date:   Tue, 15 Nov 2022 21:28:56 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...uxfoundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Julia Lawall <Julia.Lawall@...ia.fr>,
        Arnd Bergmann <arnd@...db.de>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        linux-bluetooth@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: [patch 14/15] 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.

[ tglx: Updated to the new semantics and removed the bogus claim that
  	del_timer_sync() returns the number of removal attempts ]

Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Guenter Roeck <linux@...ck-us.net>
Link: https://lore.kernel.org/r/20221110064147.712934793@goodmis.org
---
 Documentation/RCU/Design/Requirements/Requirements.rst |    2 +-
 Documentation/core-api/local_ops.rst                   |    2 +-
 Documentation/kernel-hacking/locking.rst               |   13 ++++++++-----
 3 files changed, 10 insertions(+), 7 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 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
--- 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)
     {
-            del_timer_sync(&test_timer);
+            timer_shutdown_sync(&test_timer);
     }
 
     module_init(test_init);
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -1003,11 +1003,14 @@ If 0, it means (in this case) that it is
 
 
 Another common problem is deleting timers which restart themselves (by
-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 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.
+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 del_timer_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
 =============