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Subject: Re: [PATCH] modules: Only return -EEXIST for modules that have
 finished loading
To:     linux-kernel@vger.kernel.org
Cc:     cavery@redhat.com, Jessica Yu <jeyu@kernel.org>
References: <20190402133916.13513-1-prarit@redhat.com>
From:   Prarit Bhargava <prarit@redhat.com>
Message-ID: <ccfaafb0-870a-8cc0-bf17-f4b1edb59883@redhat.com>
Date:   Mon, 8 Apr 2019 10:19:52 -0400
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Jessica?  ping?

P.

On 4/2/19 9:39 AM, Prarit Bhargava wrote:
> 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@redhat.com>
> Reported-by: Cathy Avery <cavery@redhat.com>
> Cc: Jessica Yu <jeyu@kernel.org>
> ---
>  kernel/module.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 0b9aa8ab89f0..e8c1de2ab4e1 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3566,8 +3566,7 @@ static int add_unformed_module(struct module *mod)
>  	mutex_lock(&module_mutex);
>  	old = find_module_all(mod->name, strlen(mod->name), true);
>  	if (old != NULL) {
> -		if (old->state == MODULE_STATE_COMING
> -		    || old->state == MODULE_STATE_UNFORMED) {
> +		if (old->state != MODULE_STATE_LIVE) {
>  			/* Wait in case it fails to load. */
>  			mutex_unlock(&module_mutex);
>  			err = wait_event_interruptible(module_wq,
>