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WSL2-Linux-Kernel/kernel/time
История
Thomas Gleixner 97b9410643 clockevents: Sanitize ticks to nsec conversion 
Marc Kleine-Budde pointed out, that commit 77cc982 "clocksource: use
clockevents_config_and_register() where possible" caused a regression
for some of the converted subarchs.

The reason is, that the clockevents core code converts the minimal
hardware tick delta to a nanosecond value for core internal
usage. This conversion is affected by integer math rounding loss, so
the backwards conversion to hardware ticks will likely result in a
value which is less than the configured hardware limitation. The
affected subarchs used their own workaround (SIGH!) which got lost in
the conversion.

The solution for the issue at hand is simple: adding evt->mult - 1 to
the shifted value before the integer divison in the core conversion
function takes care of it. But this only works for the case where for
the scaled math mult/shift pair "mult <= 1 << shift" is true. For the
case where "mult > 1 << shift" we can apply the rounding add only for
the minimum delta value to make sure that the backward conversion is
not less than the given hardware limit. For the upper bound we need to
omit the rounding add, because the backwards conversion is always
larger than the original latch value. That would violate the upper
bound of the hardware device.

Though looking closer at the details of that function reveals another
bogosity: The upper bounds check is broken as well. Checking for a
resulting "clc" value greater than KTIME_MAX after the conversion is
pointless. The conversion does:

      u64 clc = (latch << evt->shift) / evt->mult;

So there is no sanity check for (latch << evt->shift) exceeding the
64bit boundary. The latch argument is "unsigned long", so on a 64bit
arch the handed in argument could easily lead to an unnoticed shift
overflow. With the above rounding fix applied the calculation before
the divison is:

       u64 clc = (latch << evt->shift) + evt->mult - 1;

So we need to make sure, that neither the shift nor the rounding add
is overflowing the u64 boundary.

[ukl: move assignment to rnd after eventually changing mult, fix build
 issue and correct comment with the right math]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>
Cc: nicolas.ferre@atmel.com
Cc: Marc Pignat <marc.pignat@hevs.ch>
Cc: john.stultz@linaro.org
Cc: kernel@pengutronix.de
Cc: Ronald Wahl <ronald.wahl@raritan.com>
Cc: LAK <linux-arm-kernel@lists.infradead.org>
Cc: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1380052223-24139-1-git-send-email-u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
 		2013-10-23 12:51:21 +02:00
..
Kconfig Merge branch 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-09-04 09:36:54 -07:00
Makefile sched_clock: Make ARM's sched_clock generic for all architectures 2013-06-12 14:02:13 -07:00
alarmtimer.c alarmtimer: Export symbols of functions declared in linux/alarmtimer.h 2013-06-12 14:02:12 -07:00
clockevents.c clockevents: Sanitize ticks to nsec conversion 2013-10-23 12:51:21 +02:00
clocksource.c clocksource: Reselect clocksource when watchdog validated high-res capability 2013-07-05 11:09:28 +02:00
jiffies.c
…
ntp.c timekeeping: Fix HRTICK related deadlock from ntp lock changes 2013-09-12 07:49:51 +02:00
ntp_internal.h ntp: Rework do_adjtimex to take timespec and tai arguments 2013-04-04 13:18:15 -07:00
posix-clock.c
…
sched_clock.c sched_clock: Fix integer overflow 2013-07-22 16:24:22 -07:00
tick-broadcast.c tick: broadcast: Check broadcast mode on CPU hotplug 2013-07-12 12:35:40 +02:00
tick-common.c tick: Sanitize broadcast control logic 2013-07-02 14:26:45 +02:00
tick-internal.h clockevents: Define CS_NAME_LEN unconditionally 2013-05-28 09:28:02 +02:00
tick-oneshot.c
…
tick-sched.c Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-08-19 09:17:35 -07:00
timeconv.c
…
timekeeping.c timekeeping: Fix HRTICK related deadlock from ntp lock changes 2013-09-12 07:49:51 +02:00
timekeeping_debug.c power: Add option to log time spent in suspend 2013-05-29 12:57:34 -07:00
timekeeping_internal.h power: Add option to log time spent in suspend 2013-05-29 12:57:34 -07:00
timer_list.c timer_list: correct the iterator for timer_list 2013-08-28 19:26:38 -07:00
timer_stats.c
…