Re: INFO: rcu detected stall in hub_event

[Alan Stern]

On Thu, 21 Nov 2019, syzbot wrote:

> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    46178223 usb: gadget: add raw-gadget interface
> git tree:       https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=15a05836e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=99c88c44660624e7
> dashboard link: https://syzkaller.appspot.com/bug?extid=ec5f884c4a135aa0dbb9
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1061395ae00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13653d1ce00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+ec5f884c4a135aa0dbb9@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> rcu: INFO: rcu_sched self-detected stall on CPU

> RIP: 0010:hid_apply_multiplier drivers/hid/hid-core.c:1058 [inline]
> RIP: 0010:hid_setup_resolution_multiplier+0x33b/0x990  
> drivers/hid/hid-core.c:1114

Diagnostic patch.

#syz test: https://github.com/google/kasan.git 46178223

 drivers/hid/hid-core.c |   17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

Index: usb-devel/drivers/hid/hid-core.c
===================================================================
--- usb-devel.orig/drivers/hid/hid-core.c
+++ usb-devel/drivers/hid/hid-core.c
@@ -1055,8 +1055,13 @@ static void hid_apply_multiplier(struct
 	 */
 	multiplier_collection = &hid->collection[multiplier->usage->collection_index];
 	while (multiplier_collection->parent_idx != -1 &&
-	       multiplier_collection->type != HID_COLLECTION_LOGICAL)
+	       multiplier_collection->type != HID_COLLECTION_LOGICAL) {
+		hid_info(hid, "collection %d %px parent %d\n",
+	multiplier_collection - hid->collection, multiplier_collection,
+	multiplier_collection->parent_idx);
 		multiplier_collection = &hid->collection[multiplier_collection->parent_idx];
+	}
+	hid_info(hid, "Got collection\n");
 
 	effective_multiplier = hid_calculate_multiplier(hid, multiplier);
 
@@ -1069,6 +1074,7 @@ static void hid_apply_multiplier(struct
 						      effective_multiplier);
 		}
 	}
+	hid_info(hid, "Applied multiplier\n");
 }
 
 /*
@@ -1103,16 +1109,23 @@ void hid_setup_resolution_multiplier(str
 
 	rep_enum = &hid->report_enum[HID_FEATURE_REPORT];
 	list_for_each_entry(rep, &rep_enum->report_list, list) {
+		hid_info(hid, "Start report %px maxfield %d\n",
+	rep, rep->maxfield);
 		for (i = 0; i < rep->maxfield; i++) {
 			/* Ignore if report count is out of bounds. */
 			if (rep->field[i]->report_count < 1)
 				continue;
 
+			hid_info(hid, "Field %d %px maxusage %d\n",
+	i, rep->field[i], rep->field[i]->maxusage);
 			for (j = 0; j < rep->field[i]->maxusage; j++) {
 				usage = &rep->field[i]->usage[j];
-				if (usage->hid == HID_GD_RESOLUTION_MULTIPLIER)
+				if (usage->hid == HID_GD_RESOLUTION_MULTIPLIER) {
+					hid_info(hid, "Usage %d %px\n",
+	j, usage);
 					hid_apply_multiplier(hid,
 							     rep->field[i]);
+				}
 			}
 		}
 	}