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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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