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

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Message-ID: <20190415112313.GA4080@linux-8ccs>
Date:   Mon, 15 Apr 2019 13:23:13 +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 [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