linux-kernel - [PATCH v2 03/27] dyndbg: fix module.dyndbg handling

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Message-Id: <20220516225640.3102269-4-jim.cromie@gmail.com>
Date:   Mon, 16 May 2022 16:56:16 -0600
From:   Jim Cromie <jim.cromie@...il.com>
To:     jbaron@...mai.com, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org
Cc:     gregkh@...uxfoundation.org, daniel.vetter@...ll.ch,
        seanpaul@...omium.org, robdclark@...il.com, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, quic_saipraka@...cinc.com,
        will@...nel.org, catalin.marinas@....com,
        quic_psodagud@...cinc.com, maz@...nel.org, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, mingo@...hat.com,
        jim.cromie@...il.com, Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH v2 03/27] dyndbg: fix module.dyndbg handling

For CONFIG_DYNAMIC_DEBUG=N, the ddebug_dyndbg_module_param_cb()
stub-fn is too permissive:

bash-5.1# modprobe drm JUNKdyndbg
bash-5.1# modprobe drm dyndbgJUNK
[   42.933220] dyndbg param is supported only in CONFIG_DYNAMIC_DEBUG builds
[   42.937484] ACPI: bus type drm_connector registered

This caused no ill effects, because unknown parameters are either
ignored by default (with an "unknown parameter" warning, see below),
or ignored because dyndbg allows its no-effect use on non-dyndbg builds.

That said, the code has an explicit feedback message, which should be
issued accurately.  Fix with strcmp, for exact param-name match.

Here is fixed behavior:

bash-5.1# modprobe drm dyndbgJUNK
[   20.127473] drm: unknown parameter 'dyndbgJUNK' ignored
[   20.128835] ACPI: bus type drm_connector registered
bash-5.1# rmmod drm
[   37.961656] ACPI: bus type drm_connector unregistered
bash-5.1# modprobe drm dyndbg
[   42.933220] dyndbg param is supported only in CONFIG_DYNAMIC_DEBUG builds
[   42.937484] ACPI: bus type drm_connector registered

Reported-by: Rasmus Villemoes <linux@...musvillemoes.dk>
Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 include/linux/dynamic_debug.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index dce631e678dd..f30b01aa9fa4 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -201,7 +201,7 @@ static inline int ddebug_remove_module(const char *mod)
 static inline int ddebug_dyndbg_module_param_cb(char *param, char *val,
 						const char *modname)
 {
-	if (strstr(param, "dyndbg")) {
+	if (!strcmp(param, "dyndbg")) {
 		/* avoid pr_warn(), which wants pr_fmt() fully defined */
 		printk(KERN_WARNING "dyndbg param is supported only in "
 			"CONFIG_DYNAMIC_DEBUG builds\n");
-- 
2.35.3