On Wed, Feb 17, 2021 at 01:41:46PM +0100, Hans Verkuil wrote: > Hi Hans, > > On 17/02/2021 13:24, Hans de Goede wrote: > > <resend with the linux-media list added to the Cc> > > > > Hi Hans, > > > > Fedora has a (opt-in) system to automatically collect backtraces from software > > crashing on users systems. > > > > This includes collecting kernel backtraces (including once triggered by > > WARN macros) while looking a the top 10 of the most reported backtrace during the > > last 2 weeks report from ABRT: https://retrace.fedoraproject.org/faf/problems/ > > > > I noticed the following backtrace: > > https://retrace.fedoraproject.org/faf/problems/8150/ > > which has been reported 170000 times by Fedora users who have opted-in during the > > last 14 days. > > > > The issue here is that cec_register_adapter ends up calling request_module() > > from an async context, triggering this warn in kernel/kmod.c __request_module(): > > > > /* > > * We don't allow synchronous module loading from async. Module > > * init may invoke async_synchronize_full() which will end up > > * waiting for this task which already is waiting for the module > > * loading to complete, leading to a deadlock. > > */ > > WARN_ON_ONCE(wait && current_is_async()); > > > > The call-path leading to this goes like this: > > > > ? kvasprintf+0x6d/0xa0 > > ? kobject_set_name_vargs+0x6f/0x90 > > rc_map_get+0x30/0x60 > > It's not CEC, it is rc_map_get that calls request_module() for rc-cec.ko. > > I've added Sean Young to the CC list. > > Sean, is it possible to treat rc-cec as a built-in if MEDIA_CEC_RC is set? > > I think this issue is very specific to CEC. I would not expect to see this > with any other rc keymap. So CEC creates an RC device with a keymap (cec keymap, of course) and then the keymap needs to be loaded. We certainly don't want all keymaps as builtins, that would be a waste. The cec keymap is scanned once to build a map from cec codes to linux keycodes; making it builtin is not ideal, and makes the build system a bit messy. I don't think we can load the keymap later, user space may start remapping the keymap from udev. Possibly we could create the cec or rc device later but this could be a bit messy. Could CEC specify: #if IS_ENABLED(CONFIG_MEDIA_CEC_RC) MODULE_SOFTDEP("rc-cec") #endif ? Sean > > Regards, > > Hans > > > rc_register_device+0x108/0x510 > > cec_register_adapter+0x5c/0x280 [cec] > > drm_dp_cec_set_edid+0x11e/0x178 [drm_kms_helper] > > intel_dp_set_edid+0x8d/0xc0 [i915] > > intel_dp_detect+0x188/0x5c0 [i915] > > drm_helper_probe_single_connector_modes+0xc2/0x6d0 [drm_kms_helper] > > ? krealloc+0x7b/0xb0 > > drm_client_modeset_probe+0x25b/0x1320 [drm] > > ? kfree+0x1ea/0x200 > > ? sched_clock+0x5/0x10 > > ? sched_clock_cpu+0xc/0xa0 > > __drm_fb_helper_initial_config_and_unlock+0x37/0x470 [drm_kms_helper] > > ? _cond_resched+0x16/0x40 > > intel_fbdev_initial_config+0x14/0x30 [i915] > > async_run_entry_fn+0x39/0x160 > > > > So 2 questions: > > > > 1. Can we get this fixed please ? > > Related to this, what happens if we make this an async modprobe > > (when running from async context) is that a problem, or is it fine > > if the rc_map module gets loaded later ? > > > > 2. If the answer to 1. is "tricky", "maybe" or some such then can we > > look into a workaround here ? E.g. do we know in advance which module > > is going to be requested (1), or does that depend on the EDID data ? > > > > Regards, > > > > Hans > > > > > > 1) And can we thus do tricks with a softdep on it ? > >
