usb, kcov: collect coverage from hub_event

Add kcov_remote_start()/kcov_remote_stop() annotations to the
hub_event() function, which is responsible for processing events on USB
buses, in particular events that happen during USB device enumeration.

Since hub_event() is run in a global background kernel thread (see
Documentation/dev-tools/kcov.rst for details), each USB bus gets a
unique global handle from the USB subsystem kcov handle range.  As the
result kcov can now be used to collect coverage from events that happen
on a particular USB bus.

[akpm@linux-foundation.org: avoid patch conflicts to make life easier for Andrew]
Link: http://lkml.kernel.org/r/de4fe1c219db2d002d905dc1736e2a3bfa1db997.1572366574.git.andreyknvl@google.comSigned-off-by: NAndrey Konovalov <andreyknvl@google.com>
Reviewed-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Alexander Potapenko <glider@google.com>
Cc: Anders Roxell <anders.roxell@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Windsor <dwindsor@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Marco Elver <elver@google.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/usb/core/hub.c

@@ -18,6 +18,7 @@
 #include <linux/sched/mm.h>
 #include <linux/list.h>
 #include <linux/slab.h>
+#include <linux/kcov.h>
 #include <linux/ioctl.h>
 #include <linux/usb.h>
 #include <linux/usbdevice_fs.h>
@@ -5484,6 +5485,8 @@ static void hub_event(struct work_struct *work)
 	hub_dev = hub->intfdev;
 	intf = to_usb_interface(hub_dev);
 
+	kcov_remote_start_usb((u64)hdev->bus->busnum);
+
 	dev_dbg(hub_dev, "state %d ports %d chg %04x evt %04x\n",
 			hdev->state, hdev->maxchild,
 			/* NOTE: expects max 15 ports... */
@@ -5590,6 +5593,8 @@ static void hub_event(struct work_struct *work)
 	/* Balance the stuff in kick_hub_wq() and allow autosuspend */
 	usb_autopm_put_interface(intf);
 	kref_put(&hub->kref, hub_release);
+
+	kcov_remote_stop();
 }
 
 static const struct usb_device_id hub_id_table[] = {