On Tue, Sep 1, 2015 at 10:41 AM, Tomi Valkeinen <tomi.valkeinen@xxxxxx> wrote: > > > On 01/09/15 17:34, Rob Clark wrote: >> On Tue, Sep 1, 2015 at 6:32 AM, Tomi Valkeinen <tomi.valkeinen@xxxxxx> wrote: >>> >>> >>> On 25/08/15 22:24, Rob Clark wrote: >>>> On Tue, Aug 25, 2015 at 9:45 AM, Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: >>>>> When the usual fbcon legacy options are enabled we have >>>>> ->register_framebuffer >>>>> ->fb notifier chain calls into fbcon >>>>> ->fbcon sets up console on new fbi >>>>> ->fbi->set_par >>>>> ->drm_fb_helper_set_par exercises full kms api >>>>> >>>>> And because of locking inversion hilarity all of register_framebuffer >>>>> is done with the console lock held. Which means that the first time on >>>>> driver load we exercise _all_ the kms code (all probe paths and >>>>> modeset paths for everything connected) is under the console lock. >>>>> That means if anything goes belly-up in that big pile of code nothing >>>>> ever reaches logfiles (and the machine is dead). >>>>> >>>>> Usual tactic to debug that is to temporarily remove those console_lock >>>>> calls to be able to capture backtraces. I'm fed up writing this patch >>>>> and recompiling kernels. Hence this patch here to add an unsafe, >>>>> kernel-taining option to do this at runtime. >>>>> >>>>> Cc: Jean-Christophe Plagniol-Villard <plagnioj@xxxxxxxxxxxx> >>>>> Cc: Tomi Valkeinen <tomi.valkeinen@xxxxxx> >>>>> Cc: linux-fbdev@xxxxxxxxxxxxxxx >>>>> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx> >>>> >>>> This one was causing me some problems, if I tried to enable >>>> lockless_register_fb. It *looks* like it should work, so I'm not >>>> quite sure what the deal is. But I'm 110% fan of getting something >>>> like this working, because console_lock is pretty much the bane of kms >>>> developer's existence.. >>>> >>>> I'll have to debug further on a system where I can see more than the >>>> bottom three lines of the second to last backtrace.. >>> >>> Any idea if anyone has ever looked at properly fixing this? >> >> I hadn't had a chance to look at it further yet.. I think Daniel >> claimed it worked for him, but he was probably on intel-next, where I >> was on drm-next at the time which seemed to be having some unrelated >> i915 issues (when I was trying to debug atomic fb-helper patches). So >> can't really say that the issue I had was actually related to this >> patch. I'll try again later this week or next, when hopefully i915 in >> drm-next is in better shape.. > > Oh, I didn't mean this patch, but the whole console lock in general. > I've also banged my head to a wall because of it =). oh, not sure.. every time I've started looking closer at console/console_lock I run away screaming.. I guess if it were possible to push the lock down further so only drivers that needed the lock (presumably serial/net/etc) could take it, that would be nice.. but not sure I am that brave.. BR, -R > Tomi > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
