Re: [PATCH] modules: Only return -EEXIST for modules that have finished loading

[Jessica Yu]

+++ Prarit Bhargava [02/04/19 09:39 -0400]:
> Microsoft HyperV disables the X86_FEATURE_SMCA bit on AMD systems, and
> linux guests boot with repeated errors:
>
> amd64_edac_mod: Unknown symbol amd_unregister_ecc_decoder (err -2)
> amd64_edac_mod: Unknown symbol amd_register_ecc_decoder (err -2)
> amd64_edac_mod: Unknown symbol amd_report_gart_errors (err -2)
> amd64_edac_mod: Unknown symbol amd_unregister_ecc_decoder (err -2)
> amd64_edac_mod: Unknown symbol amd_register_ecc_decoder (err -2)
> amd64_edac_mod: Unknown symbol amd_report_gart_errors (err -2)
>
> The warnings occur because the module code erroneously returns -EEXIST
> for modules that have failed to load and are in the process of being
> removed from the module list.
>
> module amd64_edac_mod has a dependency on module edac_mce_amd.  Using
> modules.dep, systemd will load edac_mce_amd for every request of
> amd64_edac_mod.  When the edac_mce_amd module loads, the module has
> state MODULE_STATE_UNFORMED and once the module load fails and the state
> becomes MODULE_STATE_GOING.  Another request for edac_mce_amd module
> executes and add_unformed_module() will erroneously return -EEXIST even
> though the previous instance of edac_mce_amd has MODULE_STATE_GOING.
> Upon receiving -EEXIST, systemd attempts to load amd64_edac_mod, which
> fails because of unknown symbols from edac_mce_amd.
>
> add_unformed_module() must wait to return for any case other than
> MODULE_STATE_LIVE to prevent a race between multiple loads of
> dependent modules.
>
> Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx>
> Reported-by: Cathy Avery <cavery@xxxxxxxxxx>
> Cc: Jessica Yu <jeyu@xxxxxxxxxx>

Applied to modules-next. Thanks Prarit!

Jessica