Hi, On Wed, Feb 17, 2021 at 05:29:46PM +0100, Hans Verkuil wrote: > On 17/02/2021 16:11, Sean Young wrote: > > On Wed, Feb 17, 2021 at 04:04:11PM +0100, Hans de Goede wrote: > >> On 2/17/21 3:32 PM, Sean Young wrote: > >>> 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 > >> > >> That would need to be: > >> > >> MODULE_SOFTDEP("pre: rc-cec") > >> > >> I see that the drm_kms_helper and i915 drivers both depend on the cec module already, > >> so yes if that module will request for rc-cec to be loaded before it is loaded > >> (and thus before i915 is loaded) then that should work around this. > >> > >> Assuming the user is using a module-loader which honors the softdep... > >> > >> Also this assumes that rc_map_get is smart enough to not call request_module() > >> if the module is already loaded, is that the case ? > > > > Yes, see rc_map_get(). > > I tried this. It works if CONFIG_RC_CORE is set to m, but setting it to > y resulted in the same problem. It looks like MODULE_SOFTDEP only works if rc_main > is a module as well. Hmm, I'm not quite sure what is happening here. How can I reproduce this issue locally? Sean
