[Linux-kernel-mentees] [PATCH] kernel: module: Pass lockdep expression to RCU lists

[Amol Grover]

modules is traversed using list_for_each_entry_rcu outside an
RCU read-side critical section but under the protection
of module_mutex or with preemption disabled.

Hence, add corresponding lockdep expression to silence false-positive
lockdep warnings, and harden RCU lists.

list_for_each_entry_rcu when traversed inside a preempt disabled
section, doesn't need an explicit lockdep expression since it is
implicitly checked for.

Add macro for the corresponding lockdep expression.

Signed-off-by: Amol Grover <frextrite at gmail.com>
---
 kernel/module.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index b56f3224b161..2425f58159dd 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -84,6 +84,8 @@
  * 3) module_addr_min/module_addr_max.
  * (delete and add uses RCU list operations). */
 DEFINE_MUTEX(module_mutex);
+#define module_mutex_held() \
+	lockdep_is_held(&module_mutex)
 EXPORT_SYMBOL_GPL(module_mutex);
 static LIST_HEAD(modules);
 
@@ -214,7 +216,7 @@ static struct module *mod_find(unsigned long addr)
 {
 	struct module *mod;
 
-	list_for_each_entry_rcu(mod, &modules, list) {
+	list_for_each_entry_rcu(mod, &modules, list, module_mutex_held()) {
 		if (within_module(addr, mod))
 			return mod;
 	}
@@ -448,7 +450,7 @@ bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
 	if (each_symbol_in_section(arr, ARRAY_SIZE(arr), NULL, fn, data))
 		return true;
 
-	list_for_each_entry_rcu(mod, &modules, list) {
+	list_for_each_entry_rcu(mod, &modules, list, module_mutex_held()) {
 		struct symsearch arr[] = {
 			{ mod->syms, mod->syms + mod->num_syms, mod->crcs,
 			  NOT_GPL_ONLY, false },
@@ -616,7 +618,7 @@ static struct module *find_module_all(const char *name, size_t len,
 
 	module_assert_mutex_or_preempt();
 
-	list_for_each_entry_rcu(mod, &modules, list) {
+	list_for_each_entry_rcu(mod, &modules, list, module_mutex_held()) {
 		if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
 			continue;
 		if (strlen(mod->name) == len && !memcmp(mod->name, name, len))
@@ -2040,7 +2042,7 @@ void set_all_modules_text_rw(void)
 		return;
 
 	mutex_lock(&module_mutex);
-	list_for_each_entry_rcu(mod, &modules, list) {
+	list_for_each_entry_rcu(mod, &modules, list, module_mutex_held()) {
 		if (mod->state == MODULE_STATE_UNFORMED)
 			continue;
 
@@ -2059,7 +2061,7 @@ void set_all_modules_text_ro(void)
 		return;
 
 	mutex_lock(&module_mutex);
-	list_for_each_entry_rcu(mod, &modules, list) {
+	list_for_each_entry_rcu(mod, &modules, list, module_mutex_held()) {
 		/*
 		 * Ignore going modules since it's possible that ro
 		 * protection has already been disabled, otherwise we'll
-- 
2.24.1