linux-kernel - Re: INFO: rcu detected stall in hub

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Message-ID: <Pine.LNX.4.44L0.1911251622420.1565-100000@iolanthe.rowland.org>
Date:   Mon, 25 Nov 2019 16:24:05 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     syzbot <syzbot+ec5f884c4a135aa0dbb9@...kaller.appspotmail.com>
cc:     andreyknvl@...gle.com, <benjamin.tissoires@...hat.com>,
        <jikos@...nel.org>, <linux-input@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <syzkaller-bugs@...glegroups.com>
Subject: Re: INFO: rcu detected stall in hub_event

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

Index: usb-devel/drivers/hid/hid-core.c
===================================================================
--- usb-devel.orig/drivers/hid/hid-core.c
+++ usb-devel/drivers/hid/hid-core.c
@@ -1057,6 +1057,8 @@ static void hid_apply_multiplier(struct
 	while (multiplier_collection->parent_idx != -1 &&
 	       multiplier_collection->type != HID_COLLECTION_LOGICAL)
 		multiplier_collection = &hid->collection[multiplier_collection->parent_idx];
+	if (multiplier_collection->type != HID_COLLECTION_LOGICAL)
+		multiplier_collection = NULL;
 
 	effective_multiplier = hid_calculate_multiplier(hid, multiplier);
 
@@ -1191,6 +1193,9 @@ int hid_open_report(struct hid_device *d
 	}
 	device->collection_size = HID_DEFAULT_NUM_COLLECTIONS;
 
+	/* Needed for usages before the first collection */
+	device->collection[0].parent_idx = -1;
+
 	ret = -EINVAL;
 	while ((start = fetch_item(start, end, &item)) != NULL) {