Re: [PATCH v3] kernel/module.c: Only return -EEXIST for modules that have finished loading

[Jessica Yu]

+++ Prarit Bhargava [29/05/19 07:26 -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>
> Signed-off-by: Barret Rhoden <brho@xxxxxxxxxx>
> Cc: David Arcari <darcari@xxxxxxxxxx>
> Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>

Applied. Thanks!

Jessica

> ---
> kernel/module.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 6e6712b3aaf5..1e7dcbe527af 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3397,8 +3397,7 @@ static bool finished_loading(const char *name)
> 	sched_annotate_sleep();
> 	mutex_lock(&module_mutex);
> 	mod = find_module_all(name, strlen(name), true);
> -	ret = !mod || mod->state == MODULE_STATE_LIVE
> -		|| mod->state == MODULE_STATE_GOING;
> +	ret = !mod || mod->state == MODULE_STATE_LIVE;
> 	mutex_unlock(&module_mutex);
>
> 	return ret;
> @@ -3588,8 +3587,7 @@ 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,
> --
> 2.21.0