[RFC PATCH v2] usb: hub: Fix error loop seen after hub communication errors

[Guenter Roeck]

While stress testing a usb controller using a bind/unbind looop, the
following error loop was observed.

usb 7-1.2: new low-speed USB device number 3 using xhci-hcd
usb 7-1.2: hub failed to enable device, error -108
usb 7-1-port2: cannot disable (err = -22)
usb 7-1-port2: couldn't allocate usb_device
usb 7-1-port2: cannot disable (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: activate --> -22
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: activate --> -22
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: activate --> -22
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: activate --> -22
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: activate --> -22
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: activate --> -22
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: activate --> -22
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: activate --> -22
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
hub 7-1:1.0: hub_ext_port_status failed (err = -22)
** 57 printk messages dropped ** hub 7-1:1.0: activate --> -22
** 82 printk messages dropped ** hub 7-1:1.0: hub_ext_port_status failed (err = -22)

This continues forever. After adding tracebacks into the code,
the call sequence leading to this is found to be as follows.

[<ffffffc0007fc8e0>] hub_activate+0x368/0x7b8
[<ffffffc0007fceb4>] hub_resume+0x2c/0x3c
[<ffffffc00080b3b8>] usb_resume_interface.isra.6+0x128/0x158
[<ffffffc00080b5d0>] usb_suspend_both+0x1e8/0x288
[<ffffffc00080c9c4>] usb_runtime_suspend+0x3c/0x98
[<ffffffc0007820a0>] __rpm_callback+0x48/0x7c
[<ffffffc00078217c>] rpm_callback+0xa8/0xd4
[<ffffffc000786234>] rpm_suspend+0x84/0x758
[<ffffffc000786ca4>] rpm_idle+0x2c8/0x498
[<ffffffc000786ed4>] __pm_runtime_idle+0x60/0xac
[<ffffffc00080eba8>] usb_autopm_put_interface+0x6c/0x7c
[<ffffffc000803798>] hub_event+0x10ac/0x12ac
[<ffffffc000249bb8>] process_one_work+0x390/0x6b8
[<ffffffc00024abcc>] worker_thread+0x480/0x610
[<ffffffc000251a80>] kthread+0x164/0x178
[<ffffffc0002045d0>] ret_from_fork+0x10/0x40

kick_hub_wq() is called from hub_activate() even after failures to
communicate with the hub. This results in an endless sequence of
hub event -> hub activate -> wq trigger -> hub event -> ...

Provide two solutions for the problem.

- Only trigger the hub event queue if communication with the hub
  is successful.
- After a suspend failure, only resume already suspended interfaces
  if the communication with the device is still possible.

Each of the changes fixes the observed problem.

Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
v2: Instead of not triggering the hub wq after an error to submit an urb,
    implement a more complex error detection and handling. Do it in two
    places. Marked as RFC to determine if one (or both) of those solutions
    are viable.

 drivers/usb/core/driver.c | 14 ++++++++++++++
 drivers/usb/core/hub.c    | 15 ++++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index cdee5130638b..40a0ab395d82 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1331,6 +1331,20 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
 		 */
 		if (udev->parent && !PMSG_IS_AUTO(msg))
 			status = 0;
+
+		/*
+		 * If the device is inaccessible, don't try to resume
+		 * suspended interfaces and just return the error.
+		 */
+		if (status) {
+			int err;
+			u16 devstat;
+
+			err = usb_get_status(udev, USB_RECIP_DEVICE, 0,
+					     &devstat);
+			if (err)
+				goto done;
+		}
 	}
 
 	/* If the suspend failed, resume interfaces that did get suspended */
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 5a420657f9f7..8a74f483cfef 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1066,6 +1066,19 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 
 		portstatus = portchange = 0;
 		status = hub_port_status(hub, port1, &portstatus, &portchange);
+		if (status) {
+			u16 hubstatus;
+
+			ret = usb_get_status(hdev, USB_RECIP_DEVICE, 0,
+					     &hubstatus);
+			if (ret < 0) {
+				dev_err(&hdev->dev,
+					"Failed to read hub status (%d)\n",
+					ret);
+				goto abort;
+			}
+		}
+
 		if (udev || (portstatus & USB_PORT_STAT_CONNECTION))
 			dev_dbg(&port_dev->dev, "status %04x change %04x\n",
 					portstatus, portchange);
@@ -1198,7 +1211,7 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 
 	/* Scan all ports that need attention */
 	kick_hub_wq(hub);
-
+abort:
 	if (type == HUB_INIT2 || type == HUB_INIT3) {
 		/* Allow autosuspend if it was suppressed */
  disconnected:
-- 
2.7.4