Forwarded: [PATCH] WARNING: ODEBUG bug in vub300_disconnect

[syzbot <syzbot+f4a0159ce6802a0a4774@syzkaller.appspotmail.com>]

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Subject: [PATCH] WARNING: ODEBUG bug in vub300_disconnect
Author: jchuang26@m.fudan.edu.cn

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 50d05c7c76c96b90462f24debacca971d2e86713

Reported-by: syzbot+f4a0159ce6802a0a4774@syzkaller.appspotmail.com

diff --git a/drivers/mmc/host/vub300.c b/drivers/mmc/host/vub300.c
index 2dae474dc..9914c8b58 100644
--- a/drivers/mmc/host/vub300.c
+++ b/drivers/mmc/host/vub300.c
@@ -744,7 +744,11 @@ static void vub300_inactivity_timer_expired(struct timer_list *t)
 	struct vub300_mmc_host *vub300 = timer_container_of(vub300, t,
 							    inactivity_timer);
 	if (!vub300->interface) {
-		kref_put(&vub300->kref, vub300_delete);
+		/*
+		 * The disconnect/error paths have already shut this timer
+		 * down, so it can no longer be rearmed or run.
+		 */
+		return;
 	} else if (vub300->cmd) {
 		mod_timer(&vub300->inactivity_timer, jiffies + HZ);
 	} else {
@@ -2327,7 +2331,6 @@ static int vub300_probe(struct usb_interface *interface,
 	INIT_WORK(&vub300->deadwork, vub300_deadwork_thread);
 	kref_init(&vub300->kref);
 	timer_setup(&vub300->sg_transfer_timer, vub300_sg_timed_out, 0);
-	kref_get(&vub300->kref);
 	timer_setup(&vub300->inactivity_timer,
 		    vub300_inactivity_timer_expired, 0);
 	vub300->inactivity_timer.expires = jiffies + HZ;
@@ -2349,6 +2352,13 @@ static int vub300_probe(struct usb_interface *interface,
 	return 0;
 
 err_stop_io:
+	/*
+	 * The inactivity timer was armed before mmc_add_host() failed.
+	 * Shut it down before dropping the host reference so that its
+	 * callback can neither run nor be rearmed after the memory
+	 * holding the timer has been freed.
+	 */
+	timer_shutdown_sync(&vub300->inactivity_timer);
 	vub300->interface = NULL;
 	kref_put(&vub300->kref, vub300_delete);
 
@@ -2382,6 +2392,13 @@ static void vub300_disconnect(struct usb_interface *interface)
 		} else {
 			int ifnum = interface_to_InterfaceNumber(interface);
 			usb_set_intfdata(interface, NULL);
+			/*
+			 * Shut the inactivity timer down before clearing interface.
+			 * Otherwise it can be rearmed (by its own callback or by a
+			 * concurrent path that already checked interface) and later
+			 * fire after the host, which embeds the timer, is freed.
+			 */
+			timer_shutdown_sync(&vub300->inactivity_timer);
 			/* prevent more I/O from starting */
 			vub300->interface = NULL;
 			mmc_remove_host(mmc);