On Jan 17, 2008 4:38 PM, Jarek Poplawski <[EMAIL PROTECTED]> wrote: > On 17-01-2008 02:17, Dave Young wrote: > > On Jan 16, 2008 4:34 PM, Jarek Poplawski <[EMAIL PROTECTED]> wrote: > >> On Wed, Jan 16, 2008 at 09:03:03AM +0800, Dave Young wrote: > >> ... > >>> The lockdep warining was posted in the below thread, actually, I have > >>> built and run this patced kernel for several days, there's no more > >>> warnings. > >>> http://lkml.org/lkml/2008/1/3/2 > >> Right... But, with something like this: > >> > >> ... have_some_fun(... cls) > >> { > >> mutex_lock_nested(&cls->mutex, SINGLE_DEPTH_NESTING); > >> have_other_fun(cls); > >> mutex_unlock(&cls->mutex); > >> > >> } > >> > >> ... have_more_fun(...) > >> { > >> ... > >> > >> mutex_init(&cls->mutex); > >> > >> mutex_lock(&cls->mutex); > >> have_some_fun(cls); > >> mutex_unlock(&cls->mutex); > >> } > >> > >> probably you wouldn't get any lockdep warning too... > > > > Sorry for late reply. > > Actually, I don't know much about lockdep. Could you tell how to use > > it properly in this scenario? > > As you have noticed while working on this patch, if two different > instances of the same structure containig some lock are created in > the same place, lockdep will treat this one (the same) lock. It looks > strange, but actually it's a feature which enables to track > dependencies between different locks on 'class' level instead of > instance 'level'. The downside is that lockdep is very often too > sensitive by default, so you have to 'annotate' when instancess are > actually on different level (e.g. parents and children here) and > could be locked at the same time or in some order. > > You can use e.g. mutex_lock_nested() or lockdep_set_class*() for this. > Then lockdep simply trusts you, and starts to think they are different > locks. If you do it wrong there will be simply no more warnings, but > undercover lockups still possible (and diagnosing a bit harder then). > So, since in your patch there are two levels of locking, and you > started to annotate lockdep about a child taking parent's class lock > with: > mutex_lock_nested(&parent_class->mutex, SINGLE_DEPTH_NESTING); > > you should do the same everywhere in a situation like this. > lockdep will treat this simply as lock B vs. A (mutex_lock(&cls)) > dependencies.
Thanks for the explain, let me check the lockings again. > > Regards, > Jarek P. > > PS: BTW, it seems after this patch 1/1 the locking was changed a bit, > so these previous tests could be not enough. > -- 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/
