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    SubjectRe: [PATCH] tick: add check for the existence of broadcast clock event device
    On Fri, 5 Jun 2009, Feng Tang wrote:

    > >From 2f076e1867c8bbb145b74d289358174644d9fed8 Mon Sep 17 00:00:00 2001
    > From: Feng Tang <feng.tang@intel.com>
    > Date: Fri, 5 Jun 2009 10:36:15 +0800
    > Subject: [PATCH] tick: add check for the existence of broadcast clock event device
    >
    > Some platform may have no broadcast clock event device, as it use always-on
    > external timers for per-cpu timer and has no extra one for broadcast device.
    > This check will secure the access to bc device when system get some boradcast
    > on/off and enter/exit message
    >
    > Signed-off-by: Feng Tang <feng.tang@intel.com>
    > ---
    > kernel/time/tick-broadcast.c | 8 +++++++-
    > 1 files changed, 7 insertions(+), 1 deletions(-)
    >
    > diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
    > index 118a3b3..110e0bc 100644
    > --- a/kernel/time/tick-broadcast.c
    > +++ b/kernel/time/tick-broadcast.c
    > @@ -214,10 +214,13 @@ static void tick_do_broadcast_on_off(void *why)
    >
    > spin_lock_irqsave(&tick_broadcast_lock, flags);
    >
    > + bc = tick_broadcast_device.evtdev;
    > + if (!bc)
    > + goto out;
    > +

    This check is not necessary because we check whether the percpu device
    is affected by the stops in C3 madness _before_ we touch the broadcast
    device.

    if (!dev || !(dev->features & CLOCK_EVT_FEAT_C3STOP))
    got out;

    If your percpu devices are always on (not affected by C3 stop) then
    you never dereference bc. So why do we need an extra check for !bc ?

    Thanks,

    tglx


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