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	…
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	…
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	…