[PATCH v2] usb: hub: Do not attempt to autosuspend disconnected devices

[Guenter Roeck]

While running a bind/unbind stress test with the dwc3 usb driver on rk3399,
the following crash was observed.

Unable to handle kernel NULL pointer dereference at virtual address 00000218
pgd = ffffffc00165f000
[00000218] *pgd=000000000174f003, *pud=000000000174f003,
				*pmd=0000000001750003, *pte=00e8000001751713
Internal error: Oops: 96000005 [#1] PREEMPT SMP
Modules linked in: uinput uvcvideo videobuf2_vmalloc cmac
ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat rfcomm
xt_mark fuse bridge stp llc zram btusb btrtl btbcm btintel bluetooth
ip6table_filter mwifiex_pcie mwifiex cfg80211 cdc_ether usbnet r8152 mii joydev
snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device ppp_async
ppp_generic slhc tun
CPU: 1 PID: 29814 Comm: kworker/1:1 Not tainted 4.4.52 #507
Hardware name: Google Kevin (DT)
Workqueue: pm pm_runtime_work
task: ffffffc0ac540000 ti: ffffffc0af4d4000 task.ti: ffffffc0af4d4000
PC is at autosuspend_check+0x74/0x174
LR is at autosuspend_check+0x70/0x174
...
Call trace:
[<ffffffc00080dcc0>] autosuspend_check+0x74/0x174
[<ffffffc000810500>] usb_runtime_idle+0x20/0x40
[<ffffffc000785ae0>] __rpm_callback+0x48/0x7c
[<ffffffc000786af0>] rpm_idle+0x1e8/0x498
[<ffffffc000787cdc>] pm_runtime_work+0x88/0xcc
[<ffffffc000249bb8>] process_one_work+0x390/0x6b8
[<ffffffc00024abcc>] worker_thread+0x480/0x610
[<ffffffc000251a80>] kthread+0x164/0x178
[<ffffffc0002045d0>] ret_from_fork+0x10/0x40

Source:

(gdb) l *0xffffffc00080dcc0
0xffffffc00080dcc0 is in autosuspend_check
(drivers/usb/core/driver.c:1778).
1773		/* We don't need to check interfaces that are
1774		 * disabled for runtime PM.  Either they are unbound
1775		 * or else their drivers don't support autosuspend
1776		 * and so they are permanently active.
1777		 */
1778		if (intf->dev.power.disable_depth)
1779			continue;
1780		if (atomic_read(&intf->dev.power.usage_count) > 0)
1781			return -EBUSY;
1782		w |= intf->needs_remote_wakeup;

Code analysis shows that intf is set to NULL in usb_disable_device() prior
to setting actconfig to NULL. At the same time, usb_runtime_idle() does not
lock the usb device, and neither does any of the functions in the
traceback. This means that there is no protection against a race condition
where usb_disable_device() is removing dev->actconfig->interface[] pointers
while those are being accessed from autosuspend_check().

To solve the problem, synchronize and validate device state between
autosuspend_check() and usb_disconnect().

Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
v2: Do not disable autosuspend in usb_disconnect(). Instead, check the
    usb device state in autosuspend_check().
    In usb_disconnect(), call pm_runtime_barrier() earlier, immediately
    after changing the USB device state.

 drivers/usb/core/driver.c | 3 +++
 drivers/usb/core/hub.c    | 7 +++++++
 2 files changed, 10 insertions(+)

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 7ebdf2a4e8fe..eb87a259d55c 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1781,6 +1781,9 @@ static int autosuspend_check(struct usb_device *udev)
 	int			w, i;
 	struct usb_interface	*intf;
 
+	if (udev->state == USB_STATE_NOTATTACHED)
+		return -ENODEV;
+
 	/* Fail if autosuspend is disabled, or any interfaces are in use, or
 	 * any interface drivers require remote wakeup but it isn't available.
 	 */
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 57bb427c8878..fd80513aaeff 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2084,6 +2084,13 @@ void usb_disconnect(struct usb_device **pdev)
 	 * this quiesces everything except pending urbs.
 	 */
 	usb_set_device_state(udev, USB_STATE_NOTATTACHED);
+
+	/*
+	 * Ensure that the pm runtime code knows that the USB device
+	 * is in the process of being disconnected.
+	 */
+	pm_runtime_barrier(&udev->dev);
+
 	dev_info(&udev->dev, "USB disconnect, device number %d\n",
 			udev->devnum);
 
-- 
2.7.4