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

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Date:   Tue, 4 Jun 2019 16:29:31 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Barret Rhoden <brho@...gle.com>,
        David Arcari <darcari@...hat.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v3] kernel/module.c: Only return -EEXIST for modules that
 have finished loading

+++ 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@...hat.com>
>Signed-off-by: Barret Rhoden <brho@...gle.com>
>Cc: David Arcari <darcari@...hat.com>
>Cc: Jessica Yu <jeyu@...nel.org>
>Cc: Heiko Carstens <heiko.carstens@...ibm.com>

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
>