linux-kernel - Re: [tip:timers/urgent] tick: Fix oneshot broadcast setup really

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Date:	Wed, 18 Apr 2012 17:31:58 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
cc:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, suresh.b.siddha@...el.com,
	svenjoac@....de, rjw@...k.pl, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:timers/urgent] tick: Fix oneshot broadcast setup really

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@...utronix.de> wrote:
> >> Commit-ID:  b435092f70ec5ebbfb6d075d5bf3c631b49a51de
> >> Gitweb:     http://git.kernel.org/tip/b435092f70ec5ebbfb6d075d5bf3c631b49a51de
> >> Author:     Thomas Gleixner <tglx@...utronix.de>
> >> AuthorDate: Wed, 18 Apr 2012 12:08:23 +0200
> >> Committer:  Thomas Gleixner <tglx@...utronix.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@....de>
> >> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> >> Cc: Rafael J. Wysocki <rjw@...k.pl>
> >> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> >> Cc: Suresh Siddha <suresh.b.siddha@...el.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);
 }
 
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