On Tue, Aug 25, 2015 at 9:45 AM, Daniel Vetter daniel.vetter@ffwll.ch 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@jcrosoft.com Cc: Tomi Valkeinen tomi.valkeinen@ti.com Cc: linux-fbdev@vger.kernel.org Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch
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..
BR, -R
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;}
-- 1.8.3.1
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