patch "usb: hub: Do not attempt to autosuspend disconnected devices" added to usb-next

This is a note to let you know that I've just added the patch titled

usb: hub: Do not attempt to autosuspend disconnected devices

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From: Guenter Roeck <[email protected]>
Date: Mon, 20 Mar 2017 14:30:50 -0700
Subject: usb: hub: Do not attempt to autosuspend disconnected devices

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().

---
 drivers/usb/core/driver.c | 3 +++
 drivers/usb/core/hub.c    | 6 ++++++
 2 files changed, 9 insertions(+)

index 7ebdf2a4e8fe..eb87a259d55c 100644
@@ -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.
 	 */

index 735e8ab2cc1f..8f6593d7b68c 100644
@@ -2087,6 +2087,12 @@ void usb_disconnect(struct usb_device **pdev)
 	dev_info(&udev->dev, "USB disconnect, device number %d\n",
 			udev->devnum);
 
+	/*
+	 * Ensure that the pm runtime code knows that the USB device
+	 * is in the process of being disconnected.
+	 */
+	pm_runtime_barrier(&udev->dev);
+
 	usb_lock_device(udev);
 
 	hub_disconnect_children(udev);

2.12.1