Hi, 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 ? 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 ? >>> >
