linux/kernel/time
Stephen Boyd 5ae8aabeae sched_clock: Prevent callers from seeing half-updated data
The generic sched_clock registration function was previously
done lockless, due to the fact that it was expected to be called
only once. However, now there are systems that may register
multiple sched_clock sources, for which the lack of locking has
casued problems:

If two sched_clock sources are registered we may end up in a
situation where a call to sched_clock() may be accessing the
epoch cycle count for the old counter and the cycle count for the
new counter. This can lead to confusing results where
sched_clock() values jump and then are reset to 0 (due to the way
the registration function forces the epoch_ns to be 0).

Fix this by reorganizing the registration function to hold the
seqlock for as short a time as possible while we update the
clock_data structure for a new counter. We also put any
accumulated time into epoch_ns instead of resetting the time to
0 so that the clock doesn't reset after each successful
registration.

[jstultz: Added extra context to the commit message]

Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Cartwright <joshc@codeaurora.org>
Link: http://lkml.kernel.org/r/1392662736-7803-2-git-send-email-john.stultz@linaro.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2014-02-19 17:07:22 +01:00
..
alarmtimer.c alarmtimer: return EINVAL instead of ENOTSUPP if rtcdev doesn't exist 2013-10-18 16:23:58 -07:00
clockevents.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-11-12 10:36:00 +09:00
clocksource.c time: Fix signedness bug in sysfs_get_uname() and its callers 2013-10-18 16:45:58 -07:00
jiffies.c time: Fix overflow when HZ is smaller than 60 2014-02-06 16:01:40 +01:00
Kconfig nohz: Drop generic vtime obsolete dependency on CONFIG_64BIT 2013-09-30 15:37:01 +02:00
Makefile sched_clock: Make ARM's sched_clock generic for all architectures 2013-06-12 14:02:13 -07:00
ntp_internal.h ntp: Rework do_adjtimex to take timespec and tai arguments 2013-04-04 13:18:15 -07:00
ntp.c Linux 3.12-rc3 2013-10-03 07:52:21 +02:00
posix-clock.c kernel: Fix files explicitly needing EXPORT_SYMBOL infrastructure 2011-10-31 19:30:05 -04:00
sched_clock.c sched_clock: Prevent callers from seeing half-updated data 2014-02-19 17:07:22 +01:00
tick-broadcast.c tick: Clear broadcast pending bit when switching to oneshot 2014-02-13 21:55:54 +01:00
tick-common.c Merge branch 'fortglx/3.14/time' of git://git.linaro.org/people/john.stultz/linux into timers/core 2014-01-12 14:13:31 +01:00
tick-internal.h tick/timekeeping: Call update_wall_time outside the jiffies lock 2013-12-23 11:54:32 -08:00
tick-oneshot.c clockevents: Make minimum delay adjustments configurable 2011-09-08 11:10:56 +02:00
tick-sched.c Merge branch 'timers/core' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/urgent 2014-01-25 08:27:26 +01:00
timeconv.c time: add function to convert between calendar time and broken-down time for universal use 2009-09-24 07:20:56 -07:00
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
timekeeping.c Merge branch 'fortglx/3.14/time' of git://git.linaro.org/people/john.stultz/linux into timers/core 2014-01-12 14:13:31 +01:00
timer_list.c timer_list: correct the iterator for timer_list 2013-08-28 19:26:38 -07:00
timer_stats.c timer stats: Add a 'Collection: active/inactive' line to timer usage statistics 2013-10-10 09:59:25 +02:00