lkml.org 
[lkml]   [2012]   [Apr]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [tip:timers/urgent] tick: Fix oneshot broadcast setup really
    On Wednesday 18 April 2012 09:01 PM, Thomas Gleixner wrote:
    > On Wed, 18 Apr 2012, Santosh Shilimkar wrote:
    >> On Wednesday 18 April 2012 06:49 PM, Shilimkar, Santosh wrote:
    >>> On Wed, Apr 18, 2012 at 5:37 PM, tip-bot for Thomas Gleixner
    >>> <tglx@linutronix.de> wrote:
    >>>> Commit-ID: b435092f70ec5ebbfb6d075d5bf3c631b49a51de
    >>>> Gitweb: http://git.kernel.org/tip/b435092f70ec5ebbfb6d075d5bf3c631b49a51de
    >>>> Author: Thomas Gleixner <tglx@linutronix.de>
    >>>> AuthorDate: Wed, 18 Apr 2012 12:08:23 +0200
    >>>> Committer: Thomas Gleixner <tglx@linutronix.de>
    >>>> CommitDate: Wed, 18 Apr 2012 14:00:56 +0200
    >>>>
    >>>> tick: Fix oneshot broadcast setup really
    >>>>
    >>>> Sven Joachim reported, that suspend/resume on rc3 trips over a NULL
    >>>> pointer dereference. Linus spotted the clockevent handler being NULL.
    >>>>
    >>>> commit fa4da365b(clockevents: tTack broadcast device mode change in
    >>>> tick_broadcast_switch_to_oneshot()) tried to fix a problem with the
    >>>> broadcast device setup, which was introduced in commit 77b0d60c5(
    >>>> clockevents: Leave the broadcast device in shutdown mode when not
    >>>> needed).
    >>>>
    >>>> The initial commit avoided to set up the broadcast device when no
    >>>> broadcast request bits were set, but that left the broadcast device
    >>>> disfunctional. In consequence deep idle states which need the
    >>>> broadcast device were not woken up.
    >>>>
    >>>> commit fa4da365b tried to fix that by initializing the state of the
    >>>> broadcast facility, but that missed the fact, that nothing initializes
    >>>> the event handler and some other state of the underlying clock event
    >>>> device.
    >>>>
    >>>> The fix is to revert both commits and make only the mode setting of
    >>>> the clock event device conditional on the state of active broadcast
    >>>> users.
    >>>>
    >>>> That initializes everything except the low level device mode, but this
    >>>> happens when the broadcast functionality is invoked by deep idle.
    >>>>
    >>>> Reported-and-tested-by: Sven Joachim <svenjoac@gmx.de>
    >>>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    >>>> Cc: Rafael J. Wysocki <rjw@sisk.pl>
    >>>> Cc: Linus Torvalds <torvalds@linux-foundation.org>
    >>>> Cc: Suresh Siddha <suresh.b.siddha@intel.com>
    >>>> Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1204181205540.2542@ionos
    >>>>
    >>>> ---
    >>>> kernel/time/tick-broadcast.c | 7 +------
    >>>> 1 files changed, 1 insertions(+), 6 deletions(-)
    >>>>
    >>>> diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
    >>>> index bf57abd..119aca5 100644
    >>>> --- a/kernel/time/tick-broadcast.c
    >>>> +++ b/kernel/time/tick-broadcast.c
    >>>> @@ -531,7 +531,6 @@ void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
    >>>> int was_periodic = bc->mode == CLOCK_EVT_MODE_PERIODIC;
    >>>>
    >>>> bc->event_handler = tick_handle_oneshot_broadcast;
    >>>> - clockevents_set_mode(bc, CLOCK_EVT_MODE_ONESHOT);
    >>>>
    >>>> /* Take the do_timer update */
    >>>> tick_do_timer_cpu = cpu;
    >>>> @@ -549,6 +548,7 @@ void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
    >>>> to_cpumask(tmpmask));
    >>>>
    >>>> if (was_periodic && !cpumask_empty(to_cpumask(tmpmask))) {
    >>>> + clockevents_set_mode(bc, CLOCK_EVT_MODE_ONESHOT);
    >>
    >> For some reason above if() check fails in my case, so broadcast device
    >> never set to ONESHOT mode. That explains the problem I am seeing on
    >> OMAP with the $subject patch. At this point of time bc->mode is
    >> CLOCK_EVT_MODE_UNUSED.
    >
    > Darn, crap. I wonder how that works on x86
    >
    > diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
    > index bf57abd..e8f5479 100644
    > --- a/kernel/time/tick-broadcast.c
    > +++ b/kernel/time/tick-broadcast.c
    > @@ -373,6 +373,9 @@ static int tick_broadcast_set_event(ktime_t expires, int force)
    > {
    > struct clock_event_device *bc = tick_broadcast_device.evtdev;
    >
    > + if (bc->mode != CLOCK_EVT_MODE_ONESHOT)
    > + clockevents_set_mode(bc, CLOCK_EVT_MODE_ONESHOT);
    > +
    > return clockevents_program_event(bc, expires, force);
    > }
    >
    Appending above change to $subject patch makes things work
    nicely again.

    Regards
    Santosh


    \
     
     \ /
      Last update: 2012-04-18 22:37    [W:0.034 / U:31.344 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site