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authorLinus Torvalds <torvalds@linux-foundation.org>2022-12-12 12:52:02 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2022-12-12 12:52:02 -0800
commit0a1d4434db5f86c50018fe0aab299ac97dc15b76 (patch)
tree69574d3ef27cbf6527bcc38cd035d8bdf854203c /Documentation/kernel-hacking
parent79ad89123c2523a7982d457641dd64f339307e6c (diff)
parent18a207849218d8c15072f449e6d0b901262290c9 (diff)
Merge tag 'timers-core-2022-12-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer updates from Thomas Gleixner: "Updates for timers, timekeeping and drivers: Core: - The timer_shutdown[_sync]() infrastructure: Tearing down timers can be tedious when there are circular dependencies to other things which need to be torn down. A prime example is timer and workqueue where the timer schedules work and the work arms the timer. What needs to prevented is that pending work which is drained via destroy_workqueue() does not rearm the previously shutdown timer. Nothing in that shutdown sequence relies on the timer being functional. The conclusion was that the semantics of timer_shutdown_sync() should be: - timer is not enqueued - timer callback is not running - timer cannot be rearmed Preventing the rearming of shutdown timers is done by discarding rearm attempts silently. A warning for the case that a rearm attempt of a shutdown timer is detected would not be really helpful because it's entirely unclear how it should be acted upon. The only way to address such a case is to add 'if (in_shutdown)' conditionals all over the place. This is error prone and in most cases of teardown not required all. - The real fix for the bluetooth HCI teardown based on timer_shutdown_sync(). A larger scale conversion to timer_shutdown_sync() is work in progress. - Consolidation of VDSO time namespace helper functions - Small fixes for timer and timerqueue Drivers: - Prevent integer overflow on the XGene-1 TVAL register which causes an never ending interrupt storm. - The usual set of new device tree bindings - Small fixes and improvements all over the place" * tag 'timers-core-2022-12-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (34 commits) dt-bindings: timer: renesas,cmt: Add r8a779g0 CMT support dt-bindings: timer: renesas,tmu: Add r8a779g0 support clocksource/drivers/arm_arch_timer: Use kstrtobool() instead of strtobool() clocksource/drivers/timer-ti-dm: Fix missing clk_disable_unprepare in dmtimer_systimer_init_clock() clocksource/drivers/timer-ti-dm: Clear settings on probe and free clocksource/drivers/timer-ti-dm: Make timer_get_irq static clocksource/drivers/timer-ti-dm: Fix warning for omap_timer_match clocksource/drivers/arm_arch_timer: Fix XGene-1 TVAL register math error clocksource/drivers/timer-npcm7xx: Enable timer 1 clock before use dt-bindings: timer: nuvoton,npcm7xx-timer: Allow specifying all clocks dt-bindings: timer: rockchip: Add rockchip,rk3128-timer clockevents: Repair kernel-doc for clockevent_delta2ns() clocksource/drivers/ingenic-ost: Define pm functions properly in platform_driver struct clocksource/drivers/sh_cmt: Access registers according to spec vdso/timens: Refactor copy-pasted find_timens_vvar_page() helper into one copy Bluetooth: hci_qca: Fix the teardown problem for real timers: Update the documentation to reflect on the new timer_shutdown() API timers: Provide timer_shutdown[_sync]() timers: Add shutdown mechanism to the internal functions timers: Split [try_to_]del_timer[_sync]() to prepare for shutdown mode ...
Diffstat (limited to 'Documentation/kernel-hacking')
-rw-r--r--Documentation/kernel-hacking/locking.rst17
1 files changed, 10 insertions, 7 deletions
diff --git a/Documentation/kernel-hacking/locking.rst b/Documentation/kernel-hacking/locking.rst
index 6805ae6e86e6..c756786e17ae 100644
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -967,7 +967,7 @@ you might do the following::
while (list) {
struct foo *next = list->next;
- del_timer(&list->timer);
+ timer_delete(&list->timer);
kfree(list);
list = next;
}
@@ -981,7 +981,7 @@ the lock after we spin_unlock_bh(), and then try to free
the element (which has already been freed!).
This can be avoided by checking the result of
-del_timer(): if it returns 1, the timer has been deleted.
+timer_delete(): if it returns 1, the timer has been deleted.
If 0, it means (in this case) that it is currently running, so we can
do::
@@ -990,7 +990,7 @@ do::
while (list) {
struct foo *next = list->next;
- if (!del_timer(&list->timer)) {
+ if (!timer_delete(&list->timer)) {
/* Give timer a chance to delete this */
spin_unlock_bh(&list_lock);
goto retry;
@@ -1005,9 +1005,12 @@ do::
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.
+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
=============
@@ -1335,7 +1338,7 @@ lock.
- kfree()
-- add_timer() and del_timer()
+- add_timer() and timer_delete()
Mutex API reference
===================