On Fri, Apr 10, 2009 at 10:21:22PM +0200, Krzysztof Helt wrote: > On Thu, 9 Apr 2009 14:58:51 +0200 > Andrea Righi <righi.andrea@xxxxxxxxx> wrote: > > > On Thu, Apr 09, 2009 at 07:36:24PM +0800, Eric Miao wrote: > > > This happens on my Marvell PXA310-based Littleton platform with > > > Angstrom Distribution. The offending paths are many: > > > > > > FBIOPUT_VSCREENINFO: > > > lock_fb_info() > > > --> fb_set_var() > > > --> fb_notifier_call_chain() [FBINFO_MISC_USEREVENT] > > > --> fbcon_event_notifier() [FB_EVENT_MODE_CHANGE] > > > --> lock_fb_info() > > > > > > OK, now hang. I'd suggest a clean fix to the original assumption of > > > circular locking > > > issue and revert this commit first. > > > > > > -- > > > Cheers > > > - eric > > > > I can agree to revert 66c1ca019078220dc1bf968f2bb18421100ef147, since I > > don't have a clean fix for this. Pushing down fb_info->lock in > > fb_set_var() excluding to call fb_notifier_call_chain with fb_info->lock > > held doesn't seem to be so trivial... > > > > However, reverting this will re-introduce the circular locking > > dependency fb_info->lock => mm->mmap_sem => fb_info->lock. > > > > If anybody is interested I have looked into the code of the fb_mmap() > and have found that the problem Andrea tried to fix is caused > only by drivers which implements their own fb_mmap(). Krzysztof, first of all thanks for looking into the code! > > The correct solution is to push the info->lock mutex into > the fb_mmap() implemented inside the drivers. Some drivers > may not need it (the ones which only calculate offsets > and do not "real" iommaping). mmmh... I may have missed something, but the common fb_mmap() should acquire mm->mmap_sem and then info->lock, while fb_ioctl() can do that in reverse order (info->lock first and then mm->mmap_sem) causing the circular locking dependency. Are you sure that pushing info->lock down each driver's fb_mmap will fix the problem? > > I'll try to prepare a patch after the Easters. This will require a revert > of the 66c1ca commit. Thanks and happy Easter, -Andrea > > Happy Easters, > Krzysztof > > ---------------------------------------------------------------------- > Nagrody w jednym miejscu! > Sprawdz >> http://link.interia.pl/f210b > _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
