Re: [ANNOUNCE] Kernel Janitor's TODO list

[Daniel Phillips]

Rusty Russell wrote:
> 
> In message <[e-mail]> you write:
> >       http://www.uwsg.iu.edu/hypermail/linux/kernel/0005.3/0269.html
> >
> > A lot of the timer deletion races are hard to fix because of
> > the deadlock problem.
> 
> Hmmm...
> 
>         For 2.5, changing the timer interface to disallow mod_timer or
> add_timer (equivalent) on self, and making the timerfn return num
> jiffies to next run (0 = don't rerun) would solve this, right?
> I don't see a maintainable way of solving this otherwise,

It seems silly not to provide direct support for such a simple, useful
mechanism as a periodic timer.  This can be accomplished easily by
adding a field 'periodic' to struct timer_list.  If 'periodic' is
non-zero then run_timer_list uses it to set the 'expires' field and
re-inserts the timer.

For what it's worth, this is backward compatible with the existing
strategy.  The timer_list->function is still in complete control of
things if it wants to be, but forbidding it from re-adding itself sounds
like an awfully good idea.

--
Daniel