Hi Hans, On Thu, Feb 18, 2021 at 04:33:38PM +0100, Hans de Goede wrote: > On 2/17/21 5:29 PM, Hans Verkuil wrote: > > On 17/02/2021 16:11, Sean Young wrote: > >> Hi, > >> > >> 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. > > Yeah that is a known limit of module softdeps, they only work inside modules ... Yes, I assume this is the problem. > Still, assuming there is no easy other fix, we could still use this somehow. > > I do see that at least Fedora actually has CONFIG_RC_CORE=y for some reason. This is to make BPF IR decoding possible. > I guess we could maybe add the softdep to the CONFIG_RC_MAP module or > maybe to the module which contains the code enabled by CONFIG_DRM_DP_CEC ? > > At least Fedora has all drm stuff as modules and also has CONFIG_RC_MAP=m, > > I know this is not a real fix but a workaround to get rid of 170,000 > backtraces / 14 days being reported by (opted-in) systems running the > Fedora generic kernel config would be welcome regardless of it being the > "perfect" fix. Of course, I totally agree that a solution is needed. How about: 1) Use MODULE_SOFTDEP("rc-cec"); 2) If it's compiled as a module, rc-cec should be builtin Sean
