linux-kernel - [PATCH 5.6 094/167] USB: hub: Fix handling of connect changes during sleep

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Message-Id: <20200428182236.944807952@linuxfoundation.org>
Date:   Tue, 28 Apr 2020 20:24:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alan Stern <stern@...land.harvard.edu>,
        Paul Zimmerman <pauldzim@...il.com>,
        Peter Chen <peter.chen@....com>
Subject: [PATCH 5.6 094/167] USB: hub: Fix handling of connect changes during sleep

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

commit 9f952e26295d977dbfc6fedeaf8c4f112c818d37 upstream.

Commit 8099f58f1ecd ("USB: hub: Don't record a connect-change event
during reset-resume") wasn't very well conceived.  The problem it
tried to fix was that if a connect-change event occurred while the
system was asleep (such as a device disconnecting itself from the bus
when it is suspended and then reconnecting when it resumes)
requiring a reset-resume during the system wakeup transition, the hub
port's change_bit entry would remain set afterward.  This would cause
the hub driver to believe another connect-change event had occurred
after the reset-resume, which was wrong and would lead the driver to
send unnecessary requests to the device (which could interfere with a
firmware update).

The commit tried to fix this by not setting the change_bit during the
wakeup.  But this was the wrong thing to do; it means that when a
device is unplugged while the system is asleep, the hub driver doesn't
realize anything has happened: The change_bit flag which would tell it
to handle the disconnect event is clear.

The commit needs to be reverted and the problem fixed in a different
way.  Fortunately an alternative solution was noted in the commit's
Changelog: We can continue to set the change_bit entry in
hub_activate() but then clear it when a reset-resume occurs.  That way
the the hub driver will see the change_bit when a device is
disconnected but won't see it when the device is still present.

That's what this patch does.

Reported-and-tested-by: Peter Chen <peter.chen@....com>
Signed-off-by: Alan Stern <stern@...land.harvard.edu>
Fixes: 8099f58f1ecd ("USB: hub: Don't record a connect-change event during reset-resume")
Tested-by: Paul Zimmerman <pauldzim@...il.com>
CC: <stable@...r.kernel.org>
Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.2004221602480.11262-100000@iolanthe.rowland.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/core/hub.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1223,6 +1223,11 @@ static void hub_activate(struct usb_hub
 #ifdef CONFIG_PM
 			udev->reset_resume = 1;
 #endif
+			/* Don't set the change_bits when the device
+			 * was powered off.
+			 */
+			if (test_bit(port1, hub->power_bits))
+				set_bit(port1, hub->change_bits);

 		} else {
 			/* The power session is gone; tell hub_wq */
@@ -3088,6 +3093,15 @@ static int check_port_resume_type(struct
 		if (portchange & USB_PORT_STAT_C_ENABLE)
 			usb_clear_port_feature(hub->hdev, port1,
 					USB_PORT_FEAT_C_ENABLE);
+
+		/*
+		 * Whatever made this reset-resume necessary may have
+		 * turned on the port1 bit in hub->change_bits.  But after
+		 * a successful reset-resume we want the bit to be clear;
+		 * if it was on it would indicate that something happened
+		 * following the reset-resume.
+		 */
+		clear_bit(port1, hub->change_bits);
 	}

 	return status;