HID: core: Do not call request_module() in async context

request_module() may not be called form async context and in some cases
hid devices may be added from an async context. One example of this
happening is under hyperv, where this was triggering a WARN_ON in
request_module():

[   11.174497]  hid_add_device+0xee/0x2b0 [hid]
[   11.174499]  mousevsc_probe+0x223/0x2eb [hid_hyperv]
[   11.174501]  vmbus_probe+0x3a/0x90
[   11.174504]  really_probe+0x229/0x420
[   11.174506]  driver_probe_device+0x115/0x130
[   11.174507]  __driver_attach_async_helper+0x87/0x90
[   11.174509]  async_run_entry_fn+0x37/0x150

This commit skips the request_module(), falling back to the old behavior
of letting userspace deal with this, in case we are called from an async
context.

Cc: Lili Deng <v-lide@microsoft.com>
Reported-by: Lili Deng <v-lide@microsoft.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

drivers/hid/hid-core.c

@@ -30,6 +30,7 @@
 #include <linux/vmalloc.h>
 #include <linux/sched.h>
 #include <linux/semaphore.h>
+#include <linux/async.h>
 
 #include <linux/hid.h>
 #include <linux/hiddev.h>
@@ -2366,8 +2367,9 @@ int hid_add_device(struct hid_device *hdev)
 	 * not first have hid-generic binding only to have it replaced
 	 * immediately afterwards with a specialized driver.
 	 */
-	request_module("hid:b%04Xg%04Xv%08Xp%08X",
-		       hdev->bus, hdev->group, hdev->vendor, hdev->product);
+	if (!current_is_async())
+		request_module("hid:b%04Xg%04Xv%08Xp%08X", hdev->bus,
+			       hdev->group, hdev->vendor, hdev->product);
 
 	hid_debug_register(hdev, dev_name(&hdev->dev));
 	ret = device_add(&hdev->dev);