linux-kernel - [PATCH v4 06/14] dynamic_debug: use pointer comparison in ddebug_remove

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Message-Id: <20190212214150.4807-7-linux@rasmusvillemoes.dk>
Date:   Tue, 12 Feb 2019 22:41:42 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Jason Baron <jbaron@...mai.com>
Cc:     linux-kernel@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH v4 06/14] dynamic_debug: use pointer comparison in ddebug_remove_module

Now that we store the passed-in string directly in ddebug_add_module, we
can use pointer equality instead of strcmp. This is a little more
efficient, but more importantly, this also makes the code somewhat more
correct:

Currently, if one loads and then unloads a module whose name happens to
match the KBUILD_MODNAME of some built-in functionality (which need not
even be modular at all), all of their dynamic debug entries vanish along
with those of the actual module. For example, loading and unloading a
core.ko hides all pr_debugs from drivers/base/core.c and other built-in
files called core.c (incidentally, there is an in-tree module whose name
is core, but I just tested this with an out-of-tree trivial one).

Acked-by: Jason Baron <jbaron@...mai.com>
Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 lib/dynamic_debug.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 8274c4ea75e0..214828c65625 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -929,9 +929,10 @@ int ddebug_remove_module(const char *mod_name)

 	mutex_lock(&ddebug_lock);
 	list_for_each_entry_safe(dt, nextdt, &ddebug_tables, link) {
-		if (!strcmp(dt->mod_name, mod_name)) {
+		if (dt->mod_name == mod_name) {
 			ddebug_table_free(dt);
 			ret = 0;
+			break;
 		}
 	}
 	mutex_unlock(&ddebug_lock);
-- 
2.20.1