On Fri, 2007-06-08 at 19:37 +0200, Martin Peschke wrote: > Peter Zijlstra wrote: > > On Fri, 2007-06-08 at 19:18 +0200, Martin Peschke wrote: > >> Peter Zijlstra wrote: > >>> On Fri, 2007-06-08 at 19:00 +0200, Martin Peschke wrote: > >>>> Peter Zijlstra wrote: > >>>>> I'm confused as to where the class->stat objects are initialised? Is > >>>>> that done in lock_stat_init()? If so, then you have a bug. > >>>> static struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; > >>>> > >>>> I assume this gets us class structures containing all zeros, doesn't it? > >>>> Then class->stat is zeros as well, which is handled by lib/statistics. > >>>> (In this case, data gathering hasn't been turned on yet, and > >>>> statistic_inc() > >>>> and similar functions don't access other areas of struct statistic.) > >>> Who eventually calls percpu_alloc? > >> There is a small state machine calling percpu_alloc when users do > >> > >> echo state=on > /debug/statistics/lockdep/definition > >> > >> So data gathering is off by default. > >> > >> It might make sense to allow "state=on" as a default. Then allocation would > >> be done in the context of statistic_attach(). > > > > Right, the problem here is that you iterate over all_lock_classes once > > at init. > > > > Contrary to what the name might suggest, it are not all possible > > classes, just all active ones. So you'll only attach the classes which > > have been used up until the init point. All other classes used later > > will never be initialized. > > Ah.. > > Do you know where a class is setup for first use?
Somewhere down the line of lock_acquire()->register_lock_class(). It is then stuck onto the all_lock_classes list in mark_lock(). However this would be a very bad place to run init code, since percpu_alloc() can schedule and we're in the middle of a locking primitive :-) > I guess it is feasible to move statistic initialisation to that place. > > Is there a place where a class becomes unused again? Yes, it is possible to clear the task list, however that part of lockdep is a tag fragile - look for the call-chain leading to zap_class(). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
