dynamic_debug: don't duplicate modname in ddebug_add_module

For built-in modules, we're already reusing the passed-in string via
kstrdup_const().  But for actual modules (i.e.  when we're called from
dynamic_debug_setup in module.c), the passed-in string (which points at
the name[] array inside struct module) is also guaranteed to live at
least as long as the struct ddebug_table, since free_module() calls
ddebug_remove_module().

Link: http://lkml.kernel.org/r/20190212214150.4807-6-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Jason Baron <jbaron@akamai.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 8 deletions

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index dbf2b457e47e..8274c4ea75e0 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -847,17 +847,17 @@ int ddebug_add_module(struct _ddebug *tab, unsigned int n,
                              const char *name)
 {
         struct ddebug_table *dt;
-        const char *new_name;
 
         dt = kzalloc(sizeof(*dt), GFP_KERNEL);
         if (dt == NULL)
                 return -ENOMEM;
-        new_name = kstrdup_const(name, GFP_KERNEL);
-        if (new_name == NULL) {
-                kfree(dt);
-                return -ENOMEM;
-        }
-        dt->mod_name = new_name;
+        /*
+         * For built-in modules, name lives in .rodata and is
+         * immortal. For loaded modules, name points at the name[]
+         * member of struct module, which lives at least as long as
+         * this struct ddebug_table.
+         */
+        dt->mod_name = name;
         dt->num_ddebugs = n;
         dt->ddebugs = tab;
 
@@ -913,7 +913,6 @@ int ddebug_dyndbg_module_param_cb(char *param, char *val, const char *module)
 static void ddebug_table_free(struct ddebug_table *dt)
 {
         list_del_init(&dt->link);
-        kfree_const(dt->mod_name);
         kfree(dt);
 }