Thomas Gleixner a84b08314f tick/broadcast: Make broadcast device replacement work correctly ... [ Upstream commit f9d36cf445 ] When a tick broadcast clockevent device is initialized for one shot mode then tick_broadcast_setup_oneshot() OR's the periodic broadcast mode cpumask into the oneshot broadcast cpumask. This is required when switching from periodic broadcast mode to oneshot broadcast mode to ensure that CPUs which are waiting for periodic broadcast are woken up on the next tick. But it is subtly broken, when an active broadcast device is replaced and the system is already in oneshot (NOHZ/HIGHRES) mode. Victor observed this and debugged the issue. Then the OR of the periodic broadcast CPU mask is wrong as the periodic cpumask bits are sticky after tick_broadcast_enable() set it for a CPU unless explicitly cleared via tick_broadcast_disable(). That means that this sets all other CPUs which have tick broadcasting enabled at that point unconditionally in the oneshot broadcast mask. If the affected CPUs were already idle and had their bits set in the oneshot broadcast mask then this does no harm. But for non idle CPUs which were not set this corrupts their state. On their next invocation of tick_broadcast_enable() they observe the bit set, which indicates that the broadcast for the CPU is already set up. As a consequence they fail to update the broadcast event even if their earliest expiring timer is before the actually programmed broadcast event. If the programmed broadcast event is far in the future, then this can cause stalls or trigger the hung task detector. Avoid this by telling tick_broadcast_setup_oneshot() explicitly whether this is the initial switch over from periodic to oneshot broadcast which must take the periodic broadcast mask into account. In the case of initialization of a replacement device this prevents that the broadcast oneshot mask is modified. There is a second problem with broadcast device replacement in this function. The broadcast device is only armed when the previous state of the device was periodic. That is correct for the switch from periodic broadcast mode to oneshot broadcast mode as the underlying broadcast device could operate in oneshot state already due to lack of periodic state in hardware. In that case it is already armed to expire at the next tick. For the replacement case this is wrong as the device is in shutdown state. That means that any already pending broadcast event will not be armed. This went unnoticed because any CPU which goes idle will observe that the broadcast device has an expiry time of KTIME_MAX and therefore any CPUs next timer event will be earlier and cause a reprogramming of the broadcast device. But that does not guarantee that the events of the CPUs which were already in idle are delivered on time. Fix this by arming the newly installed device for an immediate event which will reevaluate the per CPU expiry times and reprogram the broadcast device accordingly. This is simpler than caching the last expiry time in yet another place or saving it before the device exchange and handing it down to the setup function. Replacement of broadcast devices is not a frequent operation and usually happens once somewhere late in the boot process. Fixes: 9c336c9935 ("tick/broadcast: Allow late registered device to enter oneshot mode") Reported-by: Victor Hassan <victor@allwinnertech.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lore.kernel.org/r/87pm7d2z1i.ffs@tglx Signed-off-by: Sasha Levin <sashal@kernel.org>		2023-05-24 17:32:31 +01:00
..
alarmtimer.c	alarmtimer: Prevent starvation by small intervals and SIG_IGN	2023-02-22 12:59:55 +01:00
clockevents.c
clocksource-wdtest.c
clocksource.c	clocksource: Suspend the watchdog temporarily when high read latency detected	2023-03-10 09:33:50 +01:00
hrtimer.c	timers: Prevent union confusion from unexpected restart_syscall()	2023-03-10 09:33:49 +01:00
itimer.c
jiffies.c
Kconfig	context_tracking: Take idle eqs entrypoints over RCU	2022-07-05 13:32:16 -07:00
Makefile
namespace.c
ntp.c
ntp_internal.h
posix-clock.c
posix-cpu-timers.c	posix-cpu-timers: Implement the missing timer_wait_running callback	2023-05-11 23:03:00 +09:00
posix-stubs.c	timers: Prevent union confusion from unexpected restart_syscall()	2023-03-10 09:33:49 +01:00
posix-timers.c	posix-cpu-timers: Implement the missing timer_wait_running callback	2023-05-11 23:03:00 +09:00
posix-timers.h
sched_clock.c
test_udelay.c	time/debug: Fix memory leak with using debugfs_lookup()	2023-03-10 09:33:52 +01:00
tick-broadcast-hrtimer.c
tick-broadcast.c	tick/broadcast: Make broadcast device replacement work correctly	2023-05-24 17:32:31 +01:00
tick-common.c	tick/common: Align tick period with the HZ tick.	2023-05-11 23:03:16 +09:00
tick-internal.h
tick-legacy.c
tick-oneshot.c
tick-sched.c	rcu: Fix missing TICK_DEP_MASK_RCU_EXP dependency check	2023-05-11 23:03:06 +09:00
tick-sched.h
time.c	time: Correct the prototype of ns_to_kernel_old_timeval and ns_to_timespec64	2022-08-09 20:02:13 +02:00
time_test.c
timeconst.bc
timeconv.c
timecounter.c
timekeeping.c	timekeeping: Fix references to nonexistent ktime_get_fast_ns()	2023-05-11 23:03:35 +09:00
timekeeping.h
timekeeping_debug.c
timekeeping_internal.h
timer.c	Random number generator updates for Linux 5.19-rc1.	2022-05-24 11:58:10 -07:00
timer_list.c
vsyscall.c