linux-kernel - [PATCH 3.16 108/294] USB: Check for dropped connection before switching to full speed

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Message-ID: <lsq.1510009382.711338306@decadent.org.uk>
Date:   Mon, 06 Nov 2017 23:03:02 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Guenter Roeck" <linux@...ck-us.net>,
        "Alan Stern" <stern@...land.harvard.edu>
Subject: [PATCH 3.16 108/294] USB: Check for dropped connection before
 switching to full speed

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Alan Stern <stern@...land.harvard.edu>

commit 94c43b9897abf4ea366ed4dba027494e080c7050 upstream.

Some buggy USB disk adapters disconnect and reconnect multiple times
during the enumeration procedure.  This may lead to a device
connecting at full speed instead of high speed, because when the USB
stack sees that a device isn't able to enumerate at high speed, it
tries to hand the connection over to a full-speed companion
controller.

The logic for doing this is careful to check that the device is still
connected.  But this check is inadequate if the device disconnects and
reconnects before the check is done.  The symptom is that a device
works, but much more slowly than it is capable of operating.

The situation was made worse recently by commit 22547c4cc4fe ("usb:
hub: Wait for connection to be reestablished after port reset"), which
increases the delay following a reset before a disconnect is
recognized, thus giving the device more time to reconnect.

This patch makes the check more robust.  If the device was
disconnected at any time during enumeration, we will now skip the
full-speed handover.

Signed-off-by: Alan Stern <stern@...land.harvard.edu>
Reported-and-tested-by: Zdenek Kabelac <zkabelac@...hat.com>
Reviewed-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/usb/core/hub.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -4602,7 +4602,8 @@ hub_power_remaining (struct usb_hub *hub
 static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
 		u16 portchange)
 {
-	int status, i;
+	int status = -ENODEV;
+	int i;
 	unsigned unit_load;
 	struct usb_device *hdev = hub->hdev;
 	struct usb_hcd *hcd = bus_to_hcd(hdev->bus);
@@ -4799,9 +4800,10 @@ loop:

 done:
 	hub_port_disable(hub, port1, 1);
-	if (hcd->driver->relinquish_port && !hub->hdev->parent)
-		hcd->driver->relinquish_port(hcd, port1);
-
+	if (hcd->driver->relinquish_port && !hub->hdev->parent) {
+		if (status != -ENOTCONN && status != -ENODEV)
+			hcd->driver->relinquish_port(hcd, port1);
+	}
 }

 /* Handle physical or logical connection change events.