module: Add support for default value for module async_probe

Add a module.async_probe kernel command line option that allows enabling
async probing for all modules. When this command line option is used,
there might still be some modules for which we want to explicitly force
synchronous probing, so extend <modulename>.async_probe to take an
optional bool input so that async probing can be disabled for a specific
module.
Signed-off-by: Saravana Kannan <saravanak@google.com>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -1152,8 +1152,12 @@
 	nopku		[X86] Disable Memory Protection Keys CPU feature found
 			in some Intel CPUs.
 
-	<module>.async_probe [KNL]
-			Enable asynchronous probe on this module.
+	<module>.async_probe[=<bool>] [KNL]
+			If no <bool> value is specified or if the value
+			specified is not a valid <bool>, enable asynchronous
+			probe on this module.  Otherwise, enable/disable
+			asynchronous probe on this module as indicated by the
+			<bool> value. See also: module.async_probe
 
 	early_ioremap_debug [KNL]
 			Enable debug messages in early_ioremap support. This
@@ -3241,6 +3245,15 @@
 			For details see:
 			Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
 
+	module.async_probe=<bool>
+			[KNL] When set to true, modules will use async probing
+			by default. To enable/disable async probing for a
+			specific module, use the module specific control that
+			is documented under <module>.async_probe. When both
+			module.async_probe and <module>.async_probe are
+			specified, <module>.async_probe takes precedence for
+			the specific module.
+
 	module.sig_enforce
 			[KNL] When CONFIG_MODULE_SIG is set, this means that
 			modules without (valid) signatures will fail to load.

kernel/module/main.c

@@ -2410,6 +2410,12 @@ static void do_free_init(struct work_struct *w)
 	}
 }
 
+#undef MODULE_PARAM_PREFIX
+#define MODULE_PARAM_PREFIX "module."
+/* Default value for module->async_probe_requested */
+static bool async_probe;
+module_param(async_probe, bool, 0644);
+
 /*
  * This is where the real work happens.
  *
@@ -2630,7 +2636,8 @@ static int unknown_module_param_cb(char *param, char *val, const char *modname,
 	int ret;
 
 	if (strcmp(param, "async_probe") == 0) {
-		mod->async_probe_requested = true;
+		if (strtobool(val, &mod->async_probe_requested))
+			mod->async_probe_requested = true;
 		return 0;
 	}
 
@@ -2797,6 +2804,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
 	if (err)
 		goto bug_cleanup;
 
+	mod->async_probe_requested = async_probe;
+
 	/* 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, mod,