linux-toradex.git/kernel/time/timekeeping.c, branch v3.10.15

timekeeping: Fix HRTICK related deadlock from ntp lock changes

2013-10-01T16:17:45+00:00

commit 7bd36014460f793c19e7d6c94dab67b0afcfcb7f upstream.

Gerlando Falauto reported that when HRTICK is enabled, it is
possible to trigger system deadlocks. These were hard to
reproduce, as HRTICK has been broken in the past, but seemed
to be connected to the timekeeping_seq lock.

Since seqlock/seqcount's aren't supported w/ lockdep, I added
some extra spinlock based locking and triggered the following
lockdep output:

[   15.849182] ntpd/4062 is trying to acquire lock:
[   15.849765]  (&(&pool->lock)->rlock){..-...}, at: [] __queue_work+0x145/0x480
[   15.850051]
[   15.850051] but task is already holding lock:
[   15.850051]  (timekeeper_lock){-.-.-.}, at: [] do_adjtimex+0x7f/0x100



[   15.850051] Chain exists of: &(&pool->lock)->rlock --> &p->pi_lock --> timekeeper_lock
[   15.850051]  Possible unsafe locking scenario:
[   15.850051]
[   15.850051]        CPU0                    CPU1
[   15.850051]        ----                    ----
[   15.850051]   lock(timekeeper_lock);
[   15.850051]                                lock(&p->pi_lock);
[   15.850051] lock(timekeeper_lock);
[   15.850051] lock(&(&pool->lock)->rlock);
[   15.850051]
[   15.850051]  *** DEADLOCK ***

The deadlock was introduced by 06c017fdd4dc48451a ("timekeeping:
Hold timekeepering locks in do_adjtimex and hardpps") in 3.10

This patch avoids this deadlock, by moving the call to
schedule_delayed_work() outside of the timekeeper lock
critical section.

Reported-by: Gerlando Falauto 
Tested-by: Lin Ming 
Signed-off-by: John Stultz 
Cc: Mathieu Desnoyers 
Link: http://lkml.kernel.org/r/1378943457-27314-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

timekeeping: Correct run-time detection of persistent_clock.

2013-05-28T20:45:19+00:00

Since commit 31ade30692dc9680bfc95700d794818fa3f754ac, timekeeping_init()
checks for presence of persistent clock by attempting to read a non-zero
time value. This is an issue on platforms where persistent_clock (instead
is implemented as a free-running counter (instead of an RTC) starting
from zero on each boot and running during suspend. Examples are some ARM
platforms (e.g. PandaBoard).

An attempt to read such a clock during timekeeping_init() may return zero
value and falsely declare persistent clock as missing. Additionally, in
the above case suspend times may be accounted twice (once from
timekeeping_resume() and once from rtc_resume()), resulting in a gradual
drift of system time.

This patch does a run-time correction of the issue by doing the same check
during timekeeping_suspend().

A better long-term solution would have to return error when trying to read
non-existing clock and zero when trying to read an uninitialized clock, but
that would require changing all persistent_clock implementations.

This patch addresses the immediate breakage, for now.

Cc: John Stultz 
Cc: Thomas Gleixner 
Cc: Feng Tang 
Cc: stable@vger.kernel.org
Signed-off-by: Zoran Markovic 
[jstultz: Tweaked commit message and subject]
Signed-off-by: John Stultz

timekeeping: Update tk->cycle_last in resume

2013-04-22T18:17:51+00:00

commit 7ec98e15aa (timekeeping: Delay update of clock->cycle_last)
forgot to update tk->cycle_last in the resume path. This results in a
stale value versus clock->cycle_last and prevents resume in the worst
case.

Reported-by: Jiri Slaby 
Reported-and-tested-by: Borislav Petkov 
Acked-by: John Stultz 
Cc: Linux-pm mailing list 
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1304211648150.21884@ionos
Signed-off-by: Thomas Gleixner

timekeeping: Make sure to notify hrtimers when TAI offset changes

2013-04-11T08:19:44+00:00

Now that we have CLOCK_TAI timers, make sure we notify hrtimer
code when TAI offset is changed.

Signed-off-by: John Stultz 
Link: http://lkml.kernel.org/r/1365622909-953-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner

timekeeping: Shorten seq_count region

2013-04-04T20:18:32+00:00

Shorten the seqcount write hold region to the actual update of the
timekeeper and the related data (e.g vsyscall).

On a contemporary x86 system this reduces the maximum latencies on
Preempt-RT from 8us to 4us on the non-timekeeping cores.

Signed-off-by: Thomas Gleixner 
Signed-off-by: John Stultz

timekeeping: Implement a shadow timekeeper

2013-04-04T20:18:32+00:00

Use the shadow timekeeper to do the update_wall_time() adjustments and
then copy it over to the real timekeeper.

Keep the shadow timekeeper in sync when updating stuff outside of
update_wall_time().

This allows us to limit the timekeeper_seq hold time to the update of
the real timekeeper and the vsyscall data in the next patch.

Signed-off-by: Thomas Gleixner 
Signed-off-by: John Stultz

timekeeping: Delay update of clock->cycle_last

2013-04-04T20:18:31+00:00

For calculating the new timekeeper values store the new cycle_last
value in the timekeeper and update the clock->cycle_last just when we
actually update the new values.

Signed-off-by: Thomas Gleixner 
Signed-off-by: John Stultz

timekeeping: Store cycle_last value in timekeeper struct as well

2013-04-04T20:18:31+00:00

For implementing a shadow timekeeper and a split calculation/update
region we need to store the cycle_last value in the timekeeper and
update the value in the clocksource struct only in the update region.

Add the extra storage to the timekeeper.

Signed-off-by: Thomas Gleixner 
Signed-off-by: John Stultz

timekeeping: Simplify tai updating from do_adjtimex

2013-04-04T20:18:16+00:00

Since we are taking the timekeeping locks, just go ahead
and update any tai change directly, rather then dropping
the lock and calling a function that will just take it again.

Cc: Thomas Gleixner 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Signed-off-by: John Stultz

timekeeping: Hold timekeepering locks in do_adjtimex and hardpps

2013-04-04T20:18:16+00:00

In moving the NTP state to be protected by the timekeeping locks,
be sure to acquire the timekeeping locks prior to calling
ntp functions.

Cc: Thomas Gleixner 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Signed-off-by: John Stultz