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? Tomi
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