hrtimers: Force migrate away hrtimers queued after CPUHP_AP_HRTIMERS_DYING

hrtimers are migrated away from the dying CPU to any online target at
the CPUHP_AP_HRTIMERS_DYING stage in order not to del

hrtimers: Force migrate away hrtimers queued after CPUHP_AP_HRTIMERS_DYING

hrtimers are migrated away from the dying CPU to any online target at
the CPUHP_AP_HRTIMERS_DYING stage in order not to delay bandwidth timers
handling tasks involved in the CPU hotplug forward progress.

However wakeups can still be performed by the outgoing CPU after
CPUHP_AP_HRTIMERS_DYING. Those can result again in bandwidth timers being
armed. Depending on several considerations (crystal ball power management
based election, earliest timer already enqueued, timer migration enabled or
not), the target may eventually be the current CPU even if offline. If that
happens, the timer is eventually ignored.

The most notable example is RCU which had to deal with each and every of
those wake-ups by deferring them to an online CPU, along with related
workarounds:

_ e787644caf76 (rcu: Defer RCU kthreads wakeup when CPU is dying)
_ 9139f93209d1 (rcu/nocb: Fix RT throttling hrtimer armed from offline CPU)
_ f7345ccc62a4 (rcu/nocb: Fix rcuog wake-up from offline softirq)

The problem isn't confined to RCU though as the stop machine kthread
(which runs CPUHP_AP_HRTIMERS_DYING) reports its completion at the end
of its work through cpu_stop_signal_done() and performs a wake up that
eventually arms the deadline server timer:

WARNING: CPU: 94 PID: 588 at kernel/time/hrtimer.c:1086 hrtimer_start_range_ns+0x289/0x2d0
CPU: 94 UID: 0 PID: 588 Comm: migration/94 Not tainted
Stopper: multi_cpu_stop+0x0/0x120 <- stop_machine_cpuslocked+0x66/0xc0
RIP: 0010:hrtimer_start_range_ns+0x289/0x2d0
Call Trace:
<TASK>
start_dl_timer
enqueue_dl_entity
dl_server_start
enqueue_task_fair
enqueue_task
ttwu_do_activate
try_to_wake_up
complete
cpu_stopper_thread

Instead of providing yet another bandaid to work around the situation, fix
it in the hrtimers infrastructure instead: always migrate away a timer to
an online target whenever it is enqueued from an offline CPU.

This will also allow to revert all the above RCU disgraceful hacks.

Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
Reported-by: Vlad Poenaru <[email protected]>
Reported-by: Usama Arif <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Tested-by: Paul E. McKenney <[email protected]>
Link: https://lore.kernel.org/all/[email protected]
Closes: [email protected]

show more ...

hrtimers: Move hrtimer base related definitions into hrtimer_defs.h

hrtimer base related struct definitions are part of hrtimers.h as it is
required there. With this, also the struct documentation w

hrtimers: Move hrtimer base related definitions into hrtimer_defs.h

hrtimer base related struct definitions are part of hrtimers.h as it is
required there. With this, also the struct documentation which is for core
code internal use, is exposed into the general api.

To prevent this, move all core internal definitions and the related
includes into hrtimer_defs.h.

Signed-off-by: Anna-Maria Behnsen <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

show more ...

hrtimer: Split out hrtimer defines into separate header

To avoid include dependency hell split out the hrtimer defines which are
required in the upcoming VDSO library into a separate header file.

[

hrtimer: Split out hrtimer defines into separate header

To avoid include dependency hell split out the hrtimer defines which are
required in the upcoming VDSO library into a separate header file.

[ tglx: Split out from the VDSO library patch and included ktime.h as
the new header depends on it. ]

Signed-off-by: Vincenzo Frascino <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Shijith Thotton <[email protected]>
Tested-by: Andre Przywara <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Russell King <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Paul Burton <[email protected]>
Cc: Daniel Lezcano <[email protected]>
Cc: Mark Salyzyn <[email protected]>
Cc: Peter Collingbourne <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Dmitry Safonov <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Huw Davies <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

show more ...