[PATCH RESEND] driver-core: fix modparam async_probe request

["Luis R. Rodriguez" <mcgrof@do-not-panic.com>]

From: "Luis R. Rodriguez" <mcgrof@suse.com>

Commit f2411da746985 ("driver-core: add driver module
asynchronous probe support") added async probe support,
in two forms:

  * in-kernel driver specification annotation
  * generic async_probe module parameter (modprobe foo async_probe)

To support the generic kernel parameter parse_args() was
extended via commit ecc8617053e0 ("module: add extra
argument for parse_params() callback") however commit
failed to f2411da746985 failed to add the required argument.

This causes a crash then whenever async_probe generic
module parameter is used. This was overlooked when the
form in which in-kernel async probe support was reworked
a bit... Fix this as originally intended.

Cc: Hannes Reinecke <hare@suse.de>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: stable@vger.kernel.org (4.2+)
Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
---

Resending and addressing Rusty, the other patch I sent on Dec 19
was addressed to Greg by mistake. Sorry about that.

 kernel/module.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 8f051a106676..88100ea77c55 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3402,16 +3402,22 @@ out:
 static int unknown_module_param_cb(char *param, char *val, const char *modname,
 				   void *arg)
 {
-	struct module *mod = arg;
+	struct module *mod;
 	int ret;
 
 	if (strcmp(param, "async_probe") == 0) {
+		mod = arg;
+		if (!mod) {
+			ret = -ENOENT;
+			goto out;
+		}
 		mod->async_probe_requested = true;
 		return 0;
 	}
 
 	/* Check for magic 'dyndbg' arg */
 	ret = ddebug_dyndbg_module_param_cb(param, val, modname);
+out:
 	if (ret != 0)
 		pr_warn("%s: unknown parameter '%s' ignored\n", modname, param);
 	return 0;
@@ -3515,7 +3521,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
 
 	/* Module is ready to execute: parsing args may do that. */
 	after_dashes = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
-				  -32768, 32767, NULL,
+				  -32768, 32767, mod,
 				  unknown_module_param_cb);
 	if (IS_ERR(after_dashes)) {
 		err = PTR_ERR(after_dashes);
-- 
2.6.2