Re: [PATCH 4/4] fbdev: Debug knob to register without holding console_lock
From: Rob Clark <hidden>
Date: 2015-08-25 19:24:08
Also in:
dri-devel, intel-gfx
On Tue, Aug 25, 2015 at 9:45 AM, Daniel Vetter [off-list ref] 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 <redacted>
Cc: Tomi Valkeinen <redacted>
Cc: linux-fbdev@vger.kernel.org
Signed-off-by: Daniel Vetter <redacted>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
quoted hunk ↗ jump to hunk
--- 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 _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel