module: move find_module check to end

I think Rusty may have made the lock a bit _too_ finegrained there, and
didn't add it to some places that needed it. It looks, for example, like
PATCH 1/2 actually drops the lock in places where it's needed
("find_module()" is documented to need it, but now load_module() didn't
hold it at all when it did the find_module()).

Rather than adding a new "module_loading" list, I think we should be able
to just use the existing "modules" list, and just fix up the locking a
bit.

In fact, maybe we could just move the "look up existing module" a bit
later - optimistically assuming that the module doesn't exist, and then
just undoing the work if it turns out that we were wrong, just before
adding ourselves to the list.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/module.c b/kernel/module.c
index d293c213c22c..28450047852a 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2226,11 +2226,6 @@ static noinline struct module *load_module(void __user *umod,
                 goto free_mod;
         }
 
-        if (find_module(mod->name)) {
-                err = -EEXIST;
-                goto free_mod;
-        }
-
         mod->state = MODULE_STATE_COMING;
 
         /* Allow arches to frob section contents and sizes.  */
@@ -2509,6 +2504,12 @@ static noinline struct module *load_module(void __user *umod,
          * The mutex protects against concurrent writers.
          */
         mutex_lock(&module_mutex);
+        if (find_module(mod->name)) {
+                err = -EEXIST;
+                /* This will also unlock the mutex */
+                goto already_exists;
+        }
+
         list_add_rcu(&mod->list, &modules);
         mutex_unlock(&module_mutex);
 
@@ -2535,6 +2536,7 @@ static noinline struct module *load_module(void __user *umod,
         mutex_lock(&module_mutex);
         /* Unlink carefully: kallsyms could be walking list. */
         list_del_rcu(&mod->list);
+ already_exists:
         mutex_unlock(&module_mutex);
         synchronize_sched();
         module_arch_cleanup(mod);