El Sat, Jan 03, 2009 at 11:13:45PM +0800 Peter Teoh ha dit:
> On Sat, Jan 3, 2009 at 6:20 PM, Microbit_Ubuntu
> <[email protected]> wrote:
> > Hello all,
> >
> > I've just joined up with this list, so this is mainly an initial "ping"
> > to see if I can post.
> > I'm a newbie studying embedded linux on an Olimex SAM9-L9260 target,
> > cross compiling on Ubuntu 8.10.
> >
> > Eventually I'd like to ask a couple of questions. On the subject of
> > timer INTs, I actually just got timer callbacks going in this sort of
> > newbie handler approach :
> >
> > static void timer_fire(unsigned long data)
> > {
> > mod_timer(&timer_ticktock, jiffies + (timer_tick*HZ));
> > printk ("Timer fired at %lu jiffies\n",jiffies);
> > }
> >
>
> since u used mod_timer(), did u also use del_timer() to delete the
> timer in your exit module code?
>
> (check for example, drivers/char/synclinkmp.c:shutdown() routine).
>
> but from kernel/timer.c these are the API for xxx_timer():
>
> EXPORT_SYMBOL(init_timer);
> EXPORT_SYMBOL(init_timer_deferrable);
> EXPORT_SYMBOL(__mod_timer);
> EXPORT_SYMBOL(mod_timer);
> EXPORT_SYMBOL(del_timer);
> EXPORT_SYMBOL(try_to_del_timer_sync);
> EXPORT_SYMBOL(del_timer_sync);
>
> so it seemed there is another del_timer_sync(), or
> try_to_del_timer_sync()....search the drivers subdirectory for
> examples....i am not sure of the differences among these.
on a smp system del_timer() could be called while the timer is
executing on another processor. this could cause a race condition
when the timer function uses resources that are freed after returning
from del_timer(). to assure that the timer isn't running after
deleting it, use del_timer_sync().
--
Matthias Kaehlcke
Embedded Linux Engineer
Barcelona
The yellow ships hung in the air just like bricks dont do
(The Hitch-Hiker's Guide to the Galaxy)
.''`.
using free software / Debian GNU/Linux | http://debian.org : :' :
`. `'`
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