linux-toradex.git/kernel/time, branch v3.10.2

tick: Fix tick_broadcast_pending_mask not cleared

2013-06-21T11:10:34+00:00

The recent modification in the cpuidle framework consolidated the
timer broadcast code across the different drivers by setting a new
flag in the idle state. It tells the cpuidle core code to enter/exit
the broadcast mode for the cpu when entering a deep idle state. The
broadcast timer enter/exit is no longer handled by the back-end
driver.

This change made the local interrupt to be enabled *before* calling
CLOCK_EVENT_NOTIFY_EXIT.

On a tegra114, a four cores system, when the flag has been introduced
in the driver, the following warning appeared:

WARNING: at kernel/time/tick-broadcast.c:578 tick_broadcast_oneshot_control
CPU: 2 PID: 0 Comm: swapper/2 Not tainted 3.10.0-rc3-next-20130529+ #15
[] (tick_broadcast_oneshot_control+0x1a4/0x1d0) from [] (tick_notify+0x240/0x40c)
[] (tick_notify+0x240/0x40c) from [] (notifier_call_chain+0x44/0x84)
[] (notifier_call_chain+0x44/0x84) from [] (raw_notifier_call_chain+0x18/0x20)
[] (raw_notifier_call_chain+0x18/0x20) from [] (clockevents_notify+0x28/0x170)
[] (clockevents_notify+0x28/0x170) from [] (cpuidle_idle_call+0x11c/0x168)
[] (cpuidle_idle_call+0x11c/0x168) from [] (arch_cpu_idle+0x8/0x38)
[] (arch_cpu_idle+0x8/0x38) from [] (cpu_startup_entry+0x60/0x134)
[] (cpu_startup_entry+0x60/0x134) from [<804fe9a4>] (0x804fe9a4)

I don't have the hardware, so I wasn't able to reproduce the warning
but after looking a while at the code, I deduced the following:

 1. the CPU2 enters a deep idle state and sets the broadcast timer

 2. the timer expires, the tick_handle_oneshot_broadcast function is
    called, setting the tick_broadcast_pending_mask and waking up the
    idle cpu CPU2

 3. the CPU2 exits idle handles the interrupt and then invokes
    tick_broadcast_oneshot_control with CLOCK_EVENT_NOTIFY_EXIT which
    runs the following code:

    [...]
    if (dev->next_event.tv64 == KTIME_MAX)
            goto out;

    if (cpumask_test_and_clear_cpu(cpu,
                                 tick_broadcast_pending_mask))
            goto out;
    [...]

    So if there is no next event scheduled for CPU2, we fulfil the
    first condition and jump out without clearing the
    tick_broadcast_pending_mask.

 4. CPU2 goes to deep idle again and calls
    tick_broadcast_oneshot_control with CLOCK_NOTIFY_EVENT_ENTER but
    with the tick_broadcast_pending_mask set for CPU2, triggering the
    warning.

The issue only surfaced due to the modifications of the cpuidle
framework, which resulted in interrupts being enabled before the call
to the clockevents code. If the call happens before interrupts have
been enabled, the warning cannot trigger, because there is still the
event pending which caused the broadcast timer expiry.

Move the check for the next event below the check for the pending bit,
so the pending bit gets cleared whether an event is scheduled on the
cpu or not.

[ tglx: Massaged changelog ]

Signed-off-by: Daniel Lezcano 
Reported-and-tested-by: Joseph Lo 
Cc: Stephen Warren 
Cc: linux-arm-kernel@lists.infradead.org
Cc: linaro-kernel@lists.linaro.org
Link: http://lkml.kernel.org/r/1371485735-31249-1-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Thomas Gleixner

tick: Remove useless timekeeping duty attribution to broadcast source

2013-05-31T13:58:32+00:00

Since 7300711e ("clockevents: broadcast fixup possible waiters"),
the timekeeping duty is assigned to the CPU that handles the tick
broadcast clock device by the time it is set in one shot mode.

This is an issue in full dynticks mode where the timekeeping duty
must stay handled by the boot CPU for now. Otherwise it prevents
secondary CPUs from offlining and this breaks
suspend/shutdown/reboot/...

As it appears there is no reason for this timekeeping duty to be
moved to the broadcast CPU, besides nothing prevent it from being
later re-assigned to another target, let's simply remove it.

Signed-off-by: Jiri Bohac 
Reported-by: Steven Rostedt 
Acked-by: Thomas Gleixner 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Paul E. McKenney 
Cc: Peter Zijlstra 
Cc: Borislav Petkov 
Signed-off-by: Frederic Weisbecker 
Signed-off-by: Ingo Molnar

nohz: Fix notifier return val that enforce timekeeping

2013-05-31T09:33:10+00:00

In tick_nohz_cpu_down_callback() if the cpu is the one handling
timekeeping, we must return something that stops the CPU_DOWN_PREPARE
notifiers and then start notify CPU_DOWN_FAILED on the already called
notifier call backs.

However traditional errno values are not handled by the notifier unless
these are encapsulated using errno_to_notifier().

Hence the current -EINVAL is misinterpreted and converted to junk after
notifier_to_errno(), leaving the notifier subsystem to random behaviour
such as eventually allowing the cpu to go down.

Fix this by using the standard NOTIFY_BAD instead.

Signed-off-by: Li Zhong 
Reviewed-by: Srivatsa S. Bhat 
Acked-by: Steven Rostedt 
Cc: Paul E. McKenney 
Cc: Ingo Molnar 
Cc: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Borislav Petkov 
Signed-off-by: Frederic Weisbecker 
Signed-off-by: Ingo Molnar

Merge branch 'fortglx/3.10/time' of git://git.linaro.org/people/jstultz/linux into timers/urgent

2013-05-29T07:55:01+00:00

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

ntp: Remove unused variable flags in __hardpps

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

kernel/time/ntp.c: In function ‘__hardpps’:
kernel/time/ntp.c:877: warning: unused variable ‘flags’

commit a076b2146fabb0894cae5e0189a8ba3f1502d737 ("ntp: Remove ntp_lock,
using the timekeeping locks to protect ntp state") removed its users,
but not the actual variable.

Signed-off-by: Geert Uytterhoeven 
Signed-off-by: John Stultz

tick: Cure broadcast false positive pending bit warning

2013-05-28T07:33:01+00:00

commit 26517f3e (tick: Avoid programming the local cpu timer if
broadcast pending) added a warning if the cpu enters broadcast mode
again while the pending bit is still set. Meelis reported that the
warning triggers. There are two corner cases which have been not
considered:

1) cpuidle calls clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER)
   twice. That can result in the following scenario

   CPU0                    CPU1
                           cpuidle_idle_call()
                             clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER)
                               set cpu in tick_broadcast_oneshot_mask

   broadcast interrupt
     event expired for cpu1
     set pending bit

                             acpi_idle_enter_simple()
                               clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER)
                                 WARN_ON(pending bit)

  Move the WARN_ON into the section where we enter broadcast mode so
  it wont provide false positives on the second call.

2) safe_halt() enables interrupts, so a broadcast interrupt can be
   delivered befor the broadcast mode is disabled. That sets the
   pending bit for the CPU which receives the broadcast
   interrupt. Though the interrupt is delivered right away from the
   broadcast handler and leaves the pending bit stale.

   Clear the pending bit for the current cpu in the broadcast handler.

Reported-and-tested-by: Meelis Roos 
Cc: Len Brown 
Cc: Frederic Weisbecker 
Cc: Borislav Petkov 
Cc: Rafael J. Wysocki 
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1305271841130.4220@ionos
Signed-off-by: Thomas Gleixner

Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2013-05-15T21:05:17+00:00

Pull timer fixes from Thomas Gleixner:

 - Cure for not using zalloc in the first place, which leads to random
   crashes with CPUMASK_OFF_STACK.

 - Revert a user space visible change which broke udev

 - Add a missing cpu_online early return introduced by the new full
   dyntick conversions

 - Plug a long standing race in the timer wheel cpu hotplug code.
   Sigh...

 - Cleanup NOHZ per cpu data on cpu down to prevent stale data on cpu
   up.

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  time: Revert ALWAYS_USE_PERSISTENT_CLOCK compile time optimizaitons
  timer: Don't reinitialize the cpu base lock during CPU_UP_PREPARE
  tick: Don't invoke tick_nohz_stop_sched_tick() if the cpu is offline
  tick: Cleanup NOHZ per cpu data on cpu down
  tick: Use zalloc_cpumask_var for allocating offstack cpumasks

time: Revert ALWAYS_USE_PERSISTENT_CLOCK compile time optimizaitons

2013-05-14T18:54:06+00:00

Kay Sievers noted that the ALWAYS_USE_PERSISTENT_CLOCK config,
which enables some minor compile time optimization to avoid
uncessary code in mostly the suspend/resume path could cause
problems for userland.

In particular, the dependency for RTC_HCTOSYS on
!ALWAYS_USE_PERSISTENT_CLOCK, which avoids setting the time
twice and simplifies suspend/resume, has the side effect
of causing the /sys/class/rtc/rtcN/hctosys flag to always be
zero, and this flag is commonly used by udev to setup the
/dev/rtc symlink to /dev/rtcN, which can cause pain for
older applications.

While the udev rules could use some work to be less fragile,
breaking userland should strongly be avoided. Additionally
the compile time optimizations are fairly minor, and the code
being optimized is likely to be reworked in the future, so
lets revert this change.

Reported-by: Kay Sievers 
Signed-off-by: John Stultz 
Cc: stable  #3.9
Cc: Feng Tang 
Cc: Jason Gunthorpe 
Link: http://lkml.kernel.org/r/1366828376-18124-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner

tick: Don't invoke tick_nohz_stop_sched_tick() if the cpu is offline

2013-05-14T15:40:31+00:00

commit 5b39939a4 (nohz: Move ts->idle_calls incrementation into strict
idle logic) moved code out of tick_nohz_stop_sched_tick() and missed
to bail out when the cpu is offline. That's causing subsequent
failures as an offline CPU is supposed to die and not to fiddle with
nohz magic.

Return false in can_stop_idle_tick() if the cpu is offline.

Reported-and-tested-by: Jiri Kosina 
Reported-and-tested-by: Prarit Bhargava 
Cc: Frederic Weisbecker 
Cc: Borislav Petkov 
Cc: Tony Luck 
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1305132138160.2863@ionos
Signed-off-by: Thomas Gleixner