linux-kernel - [PATCH AUTOSEL 4.9 06/30] kernel/module.c: Only return -EEXIST for modules that have finished loading

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Message-Id: <20190726134432.12993-6-sashal@kernel.org>
Date:   Fri, 26 Jul 2019 09:44:08 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Prarit Bhargava <prarit@...hat.com>,
        Barret Rhoden <brho@...gle.com>,
        David Arcari <darcari@...hat.com>,
        Jessica Yu <jeyu@...nel.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.9 06/30] kernel/module.c: Only return -EEXIST for modules that have finished loading

From: Prarit Bhargava <prarit@...hat.com>

[ Upstream commit 6e6de3dee51a439f76eb73c22ae2ffd2c9384712 ]

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>
Signed-off-by: Jessica Yu <jeyu@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/module.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 2325c9821f2a..fb9e07aec49e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3351,8 +3351,7 @@ 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;
@@ -3515,8 +3514,7 @@ 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,
-- 
2.20.1