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

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Date:   Mon, 15 Apr 2019 15:20:43 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     linux-kernel@...r.kernel.org, cavery@...hat.com
Subject: Re: [PATCH] modules: Only return -EEXIST for modules that have
 finished loading

+++ Prarit Bhargava [15/04/19 08:04 -0400]:
>
>
>On 4/15/19 7:23 AM, Jessica Yu wrote:
>> +++ 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@...hat.com>
>>> Reported-by: Cathy Avery <cavery@...hat.com>
>>> Cc: Jessica Yu <jeyu@...nel.org>
>>
>> Applied to modules-next. Thanks Prarit!
>
>Jessica, could I have the URL of the git tree?

Sure, you can find the modules-next branch at:

    git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux.git

Thanks,

Jessica