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@jcrosoft.com Cc: Tomi Valkeinen tomi.valkeinen@ti.com Cc: linux-fbdev@vger.kernel.org Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch --- drivers/video/fbdev/core/fbmem.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 0705d8883ede..4e73b6f6b1c0 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1608,6 +1608,11 @@ static int do_remove_conflicting_framebuffers(struct apertures_struct *a, return 0; }
+static bool lockless_register_fb; +module_param_named_unsafe(lockless_register_fb, lockless_register_fb, bool, 0400); +MODULE_PARM_DESC(lockless_register_fb, + "Lockless framebuffer registration for debugging [default=off]"); + static int do_register_framebuffer(struct fb_info *fb_info) { int i, ret; @@ -1675,15 +1680,18 @@ static int do_register_framebuffer(struct fb_info *fb_info) registered_fb[i] = fb_info;
event.info = fb_info; - console_lock(); + if (!lockless_register_fb) + console_lock(); if (!lock_fb_info(fb_info)) { - console_unlock(); + if (!lockless_register_fb) + console_unlock(); return -ENODEV; }
fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event); unlock_fb_info(fb_info); - console_unlock(); + if (!lockless_register_fb) + console_unlock(); return 0; }