1 files changed, 22 insertions, 25 deletions

diff --git a/kernel/module.c b/kernel/module.c
index 3d256681ab64..c0f1826e2d9e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -42,6 +42,7 @@
 #include <linux/string.h>
 #include <linux/mutex.h>
 #include <linux/unwind.h>
+#include <linux/rculist.h>
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
 #include <linux/license.h>
@@ -63,7 +64,7 @@
 #define INIT_OFFSET_MASK (1UL << (BITS_PER_LONG-1))
 
 /* List of modules, protected by module_mutex or preempt_disable
- * (add/delete uses stop_machine). */
+ * (delete uses stop_machine/add uses RCU list operations). */
 static DEFINE_MUTEX(module_mutex);
 static LIST_HEAD(modules);
 
@@ -241,7 +242,7 @@ static bool each_symbol(bool (*fn)(const struct symsearch *arr,
         if (each_symbol_in_section(arr, ARRAY_SIZE(arr), NULL, fn, data))
                 return true;
 
-        list_for_each_entry(mod, &modules, list) {
+        list_for_each_entry_rcu(mod, &modules, list) {
                 struct symsearch arr[] = {
                         { mod->syms, mod->syms + mod->num_syms, mod->crcs,
                           NOT_GPL_ONLY, false },
@@ -1417,17 +1418,6 @@ static void mod_kobject_remove(struct module *mod)
 }
 
 /*
- * link the module with the whole machine is stopped with interrupts off
- * - this defends against kallsyms not taking locks
- */
-static int __link_module(void *_mod)
-{
-        struct module *mod = _mod;
-        list_add(&mod->list, &modules);
-        return 0;
-}
-
-/*
  * unlink the module with the whole machine is stopped with interrupts off
  * - this defends against kallsyms not taking locks
  */
@@ -2239,9 +2229,13 @@ static noinline struct module *load_module(void __user *umod,
                        mod->name);
 
         /* Now sew it into the lists so we can get lockdep and oops
-         * info during argument parsing.  Noone should access us, since
-         * strong_try_module_get() will fail. */
-        stop_machine(__link_module, mod, NULL);
+         * info during argument parsing.  Noone should access us, since
+         * strong_try_module_get() will fail.
+         * lockdep/oops can run asynchronous, so use the RCU list insertion
+         * function to insert in a way safe to concurrent readers.
+         * The mutex protects against concurrent writers.
+         */
+        list_add_rcu(&mod->list, &modules);
 
         err = parse_args(mod->name, mod->args, kp, num_kp, NULL);
         if (err < 0)
@@ -2436,7 +2430,7 @@ const char *module_address_lookup(unsigned long addr,
         const char *ret = NULL;
 
         preempt_disable();
-        list_for_each_entry(mod, &modules, list) {
+        list_for_each_entry_rcu(mod, &modules, list) {
                 if (within(addr, mod->module_init, mod->init_size)
                     || within(addr, mod->module_core, mod->core_size)) {
                         if (modname)
@@ -2459,7 +2453,7 @@ int lookup_module_symbol_name(unsigned long addr, char *symname)
         struct module *mod;
 
         preempt_disable();
-        list_for_each_entry(mod, &modules, list) {
+        list_for_each_entry_rcu(mod, &modules, list) {
                 if (within(addr, mod->module_init, mod->init_size) ||
                     within(addr, mod->module_core, mod->core_size)) {
                         const char *sym;
@@ -2483,7 +2477,7 @@ int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size,
         struct module *mod;
 
         preempt_disable();
-        list_for_each_entry(mod, &modules, list) {
+        list_for_each_entry_rcu(mod, &modules, list) {
                 if (within(addr, mod->module_init, mod->init_size) ||
                     within(addr, mod->module_core, mod->core_size)) {
                         const char *sym;
@@ -2510,7 +2504,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
         struct module *mod;
 
         preempt_disable();
-        list_for_each_entry(mod, &modules, list) {
+        list_for_each_entry_rcu(mod, &modules, list) {
                 if (symnum < mod->num_symtab) {
                         *value = mod->symtab[symnum].st_value;
                         *type = mod->symtab[symnum].st_info;
@@ -2553,7 +2547,7 @@ unsigned long module_kallsyms_lookup_name(const char *name)
                         ret = mod_find_symname(mod, colon+1);
                 *colon = ':';
         } else {
-                list_for_each_entry(mod, &modules, list)
+                list_for_each_entry_rcu(mod, &modules, list)
                         if ((ret = mod_find_symname(mod, name)) != 0)
                                 break;
         }
@@ -2656,7 +2650,7 @@ const struct exception_table_entry *search_module_extables(unsigned long addr)
         struct module *mod;
 
         preempt_disable();
-        list_for_each_entry(mod, &modules, list) {
+        list_for_each_entry_rcu(mod, &modules, list) {
                 if (mod->num_exentries == 0)
                         continue;
 
@@ -2682,7 +2676,7 @@ int is_module_address(unsigned long addr)
 
         preempt_disable();
 
-        list_for_each_entry(mod, &modules, list) {
+        list_for_each_entry_rcu(mod, &modules, list) {
                 if (within(addr, mod->module_core, mod->core_size)) {
                         preempt_enable();
                         return 1;
@@ -2703,7 +2697,7 @@ struct module *__module_text_address(unsigned long addr)
         if (addr < module_addr_min || addr > module_addr_max)
                 return NULL;
 
-        list_for_each_entry(mod, &modules, list)
+        list_for_each_entry_rcu(mod, &modules, list)
                 if (within(addr, mod->module_init, mod->init_text_size)
                     || within(addr, mod->module_core, mod->core_text_size))
                         return mod;
@@ -2728,8 +2722,11 @@ void print_modules(void)
         char buf[8];
 
         printk("Modules linked in:");
-        list_for_each_entry(mod, &modules, list)
+        /* Most callers should already have preempt disabled, but make sure */
+        preempt_disable();
+        list_for_each_entry_rcu(mod, &modules, list)
                 printk(" %s%s", mod->name, module_flags(mod, buf));
+        preempt_enable();
         if (last_unloaded_module[0])
                 printk(" [last unloaded: %s]", last_unloaded_module);
         printk("\n");