From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx> 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@xxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx> Link: https://lore.kernel.org/r/20221110064147.712934793@xxxxxxxxxxx --- 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 =============
