Re: module: fix ddebug_remove_module()

From: Jessica Yu
Date: Tue Jul 11 2017 - 10:32:50 EST

+++ Zhou Chengming [07/07/17 11:15 +0800]:
ddebug_remove_module() use mod->name to find the ddebug_table of the
module and remove it. But dynamic_debug_setup() use the first
_ddebug->modname to create ddebug_table for the module. It's ok when
the _ddebug->modname is the same with the mod->name.

But livepatch module is special, it may contain _ddebugs of other
modules, the modname of which is different from the name of livepatch
module. So ddebug_remove_module() can't use mod->name to find the

s/mod->name/_ddebug->modname/ :) I'll fix the typo in the changelog.

right ddebug_table and remove it. It can cause kernel crash when we cat
the file <debugfs>/dynamic_debug/control.

Signed-off-by: Zhou Chengming <zhouchengming1@xxxxxxxxxx>

Makes sense, I have this queued up to be applied to modules-next.

By the way, although I can see how livepatch modules can end up
including a hodgepodge of _ddebug entries from different modules,
wouldn't the correct thing to do be to have the modname of the
livepatch module instead of the modules they originally came from? I
think when the pr_debug's are enabled it'll print the name of the
original module instead of the livepatch module.


kernel/module.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 4a3665f..dac9805 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2703,21 +2703,21 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
#endif /* CONFIG_KALLSYMS */

-static void dynamic_debug_setup(struct _ddebug *debug, unsigned int num)
+static void dynamic_debug_setup(struct module *mod, struct _ddebug *debug, unsigned int num)
if (!debug)
- if (ddebug_add_module(debug, num, debug->modname))
+ if (ddebug_add_module(debug, num, mod->name))
pr_err("dynamic debug error adding module: %s\n",

-static void dynamic_debug_remove(struct _ddebug *debug)
+static void dynamic_debug_remove(struct module *mod, struct _ddebug *debug)
if (debug)
- ddebug_remove_module(debug->modname);
+ ddebug_remove_module(mod->name);

void * __weak module_alloc(unsigned long size)
@@ -3697,7 +3697,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
goto free_arch_cleanup;

- dynamic_debug_setup(info->debug, info->num_debug);
+ dynamic_debug_setup(mod, info->debug, info->num_debug);

/* Ftrace init must be called in the MODULE_STATE_UNFORMED state */
@@ -3761,7 +3761,7 @@ static int load_module(struct load_info *info, const char __user *uargs,

- dynamic_debug_remove(info->debug);
+ dynamic_debug_remove(mod, info->debug);