linux.git/kernel/time/tick-broadcast.c, branch v5.10.258

tick/broadcast: Move per CPU pointer access into the atomic section

2024-08-19T03:41:18+00:00

commit 6881e75237a84093d0986f56223db3724619f26e upstream.

The recent fix for making the take over of the broadcast timer more
reliable retrieves a per CPU pointer in preemptible context.

This went unnoticed as compilers hoist the access into the non-preemptible
region where the pointer is actually used. But of course it's valid that
the compiler keeps it at the place where the code puts it which rightfully
triggers:

  BUG: using smp_processor_id() in preemptible [00000000] code:
       caller is hotplug_cpu__broadcast_tick_pull+0x1c/0xc0

Move it to the actual usage site which is in a non-preemptible region.

Fixes: f7d43dd206e7 ("tick/broadcast: Make takeover of broadcast hrtimer reliable")
Reported-by: David Wang <00107082@163.com>
Signed-off-by: Thomas Gleixner 
Tested-by: Yu Liao 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/87ttg56ers.ffs@tglx
Signed-off-by: Greg Kroah-Hartman

tick/broadcast: Make takeover of broadcast hrtimer reliable

2024-08-19T03:40:55+00:00

commit f7d43dd206e7e18c182f200e67a8db8c209907fa upstream.

Running the LTP hotplug stress test on a aarch64 machine results in
rcu_sched stall warnings when the broadcast hrtimer was owned by the
un-plugged CPU. The issue is the following:

CPU1 (owns the broadcast hrtimer)	CPU2

				tick_broadcast_enter()
				  // shutdown local timer device
				  broadcast_shutdown_local()
				...
				tick_broadcast_exit()
				  clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT)
				  // timer device is not programmed
				  cpumask_set_cpu(cpu, tick_broadcast_force_mask)

				initiates offlining of CPU1
take_cpu_down()
/*
 * CPU1 shuts down and does not
 * send broadcast IPI anymore
 */
				takedown_cpu()
				  hotplug_cpu__broadcast_tick_pull()
				    // move broadcast hrtimer to this CPU
				    clockevents_program_event()
				      bc_set_next()
					hrtimer_start()
					/*
					 * timer device is not programmed
					 * because only the first expiring
					 * timer will trigger clockevent
					 * device reprogramming
					 */

What happens is that CPU2 exits broadcast mode with force bit set, then the
local timer device is not reprogrammed and CPU2 expects to receive the
expired event by the broadcast IPI. But this does not happen because CPU1
is offlined by CPU2. CPU switches the clockevent device to ONESHOT state,
but does not reprogram the device.

The subsequent reprogramming of the hrtimer broadcast device does not
program the clockevent device of CPU2 either because the pending expiry
time is already in the past and the CPU expects the event to be delivered.
As a consequence all CPUs which wait for a broadcast event to be delivered
are stuck forever.

Fix this issue by reprogramming the local timer device if the broadcast
force bit of the CPU is set so that the broadcast hrtimer is delivered.

[ tglx: Massage comment and change log. Add Fixes tag ]

Fixes: 989dcb645ca7 ("tick: Handle broadcast wakeup of multiple cpus")
Signed-off-by: Yu Liao 
Signed-off-by: Thomas Gleixner 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240711124843.64167-1-liaoyu15@huawei.com
Signed-off-by: Greg Kroah-Hartman

tick: Get rid of tick_period

2023-05-17T09:47:46+00:00

[ Upstream commit b996544916429946bf4934c1c01a306d1690972c ]

The variable tick_period is initialized to NSEC_PER_TICK / HZ during boot
and never updated again.

If NSEC_PER_TICK is not an integer multiple of HZ this computation is less
accurate than TICK_NSEC which has proper rounding in place.

Aside of the inaccuracy there is no reason for having this variable at
all. It's just a pointless indirection and all usage sites can just use the
TICK_NSEC constant.

Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20201117132006.766643526@linutronix.de
Stable-dep-of: e9523a0d8189 ("tick/common: Align tick period with the HZ tick.")
Signed-off-by: Sasha Levin

treewide: Use fallthrough pseudo-keyword

2020-08-23T22:36:59+00:00

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva

tick: Fix typos in comments

2019-04-19T17:17:04+00:00

Signed-off-by: Laurent Gauthier 
Cc: Frederic Weisbecker 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Signed-off-by: Ingo Molnar

tick/broadcast: Fix warning about undefined tick_broadcast_oneshot_offline()

2019-03-29T13:13:44+00:00

Randconfig builds with

  CONFIG_TICK_ONESHOT=y
  CONFIG_HOTPLUG_CPU=n

trigger

  kernel/time/tick-broadcast.c:39:13: warning: ‘tick_broadcast_oneshot_offline’ \
	  declared ‘static’ but never defined [-Wunused-function]

due to that function's definition missing.

Move the CONFIG_HOTPLUG_CPU ifdeffery around its declaration too.

Fixes: 1b72d4323798 ("tick: Remove outgoing CPU from broadcast masks")
Signed-off-by: Borislav Petkov 
Acked-by: Thomas Gleixner 
Reviewed-by: Mukesh Ojha 
Cc: Valentin Schneider 
Cc: Frederic Weisbecker 
Cc: x86@kernel.org
Link: https://lkml.kernel.org/r/20190329110508.6621-1-bp@alien8.de

tick: Remove outgoing CPU from broadcast masks

2019-03-23T17:26:43+00:00

Valentin reported that unplugging a CPU occasionally results in a warning
in the tick broadcast code which is triggered when an offline CPU is in the
broadcast mask.

This happens because the outgoing CPU is not removing itself from the
broadcast masks, especially not from the broadcast_force_mask. The removal
happens on the control CPU after the outgoing CPU is dead. It's a long
standing issue, but the warning is harmless.

Rework the hotplug mechanism so that the outgoing CPU removes itself from
the broadcast masks after disabling interrupts and removing itself from the
online mask.

Reported-by: Valentin Schneider 
Signed-off-by: Thomas Gleixner 
Tested-by: Valentin Schneider 
Cc: Frederic Weisbecker 
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1903211540180.1784@nanos.tec.linutronix.de

timers: Mark expected switch fall-throughs

2019-01-29T19:08:42+00:00

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where fall through is indeed expected.

Signed-off-by: Gustavo A. R. Silva 
Signed-off-by: Thomas Gleixner 
Cc: Frederic Weisbecker 
Cc: John Stultz 
Cc: Stephen Boyd 
Link: https://lkml.kernel.org/r/20190123081413.GA3949@embeddedor

hrtimers/tick/clockevents: Remove sloppy license references

2018-11-23T10:51:21+00:00

"For licencing details see kernel-base/COPYING" and similar license
references have no value over the SPDX identifier. Remove them.

Signed-off-by: Thomas Gleixner 
Acked-by: Kees Cook 
Acked-by: Ingo Molnar 
Acked-by: John Stultz 
Acked-by: Corey Minyard 
Cc: Peter Zijlstra 
Cc: Kate Stewart 
Cc: Philippe Ombredanne 
Cc: Peter Anvin 
Cc: Russell King 
Cc: Richard Cochran 
Cc: "Paul E. McKenney" 
Cc: Nicolas Pitre 
Cc: David Riley 
Cc: Colin Cross 
Cc: Mark Brown 
Link: https://lkml.kernel.org/r/20181031182252.963632760@linutronix.de

time: Add SPDX license identifiers

2018-11-23T10:51:20+00:00

Update the time(r) core files files with the correct SPDX license
identifier based on the license text in the file itself. The SPDX
identifier is a legally binding shorthand, which can be used instead of the
full boiler plate text.

This work is based on a script and data from Philippe Ombredanne, Kate
Stewart and myself. The data has been created with two independent license
scanners and manual inspection.

The following files do not contain any direct license information and have
been omitted from the big initial SPDX changes:

  timeconst.bc: The .bc files were not touched
  time.c, timer.c, timekeeping.c: Licence was deduced from EXPORT_SYMBOL_GPL

As those files do not contain direct license references they fall under the
project license, i.e. GPL V2 only.

Signed-off-by: Thomas Gleixner 
Acked-by: Kees Cook 
Acked-by: Ingo Molnar 
Acked-by: John Stultz 
Acked-by: Corey Minyard 
Cc: Peter Zijlstra 
Cc: Kate Stewart 
Cc: Philippe Ombredanne 
Cc: Russell King 
Cc: Richard Cochran 
Cc: Nicolas Pitre 
Cc: David Riley 
Cc: Colin Cross 
Cc: Mark Brown 
Cc: H. Peter Anvin 
Cc: Paul E. McKenney 
Link: https://lkml.kernel.org/r/20181031182252.879109557@linutronix.de