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From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
To:     Jason Baron <jbaron@akamai.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>
Subject: [PATCH 08/22] dynamic_debug: don't duplicate modname in ddebug_add_module
Date:   Thu, 20 Sep 2018 00:04:30 +0200
Message-Id: <20180919220444.23190-9-linux@rasmusvillemoes.dk>
In-Reply-To: <20180919220444.23190-1-linux@rasmusvillemoes.dk>
References: <20180919220444.23190-1-linux@rasmusvillemoes.dk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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().

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 lib/dynamic_debug.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index c7c96bc7654a..2155e0e23530 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);
 }
 
-- 
2.16.4