<feed xmlns='http://www.w3.org/2005/Atom'>
<title>linux-stable.git/drivers/usb/storage, branch v4.4.220</title>
<subtitle>Linux kernel stable tree</subtitle>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/'/>
<entry>
<title>usb: storage: Add quirk for Samsung Fit flash</title>
<updated>2020-03-11T06:51:17+00:00</updated>
<author>
<name>Jim Lin</name>
<email>jilin@nvidia.com</email>
</author>
<published>2020-03-02T14:21:35+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=ccd487f072897a72036d31801d6553fabbd97315'/>
<id>ccd487f072897a72036d31801d6553fabbd97315</id>
<content type='text'>
commit 86d92f5465958752481269348d474414dccb1552 upstream.

Current driver has 240 (USB2.0) and 2048 (USB3.0) as max_sectors,
e.g., /sys/bus/scsi/devices/0:0:0:0/max_sectors

If data access times out, driver error handling will issue a port
reset.
Sometimes Samsung Fit (090C:1000) flash disk will not respond to
later Set Address or Get Descriptor command.

Adding this quirk to limit max_sectors to 64 sectors to avoid issue
occurring.

Signed-off-by: Jim Lin &lt;jilin@nvidia.com&gt;
Acked-by: Alan Stern &lt;stern@rowland.harvard.edu&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/1583158895-31342-1-git-send-email-jilin@nvidia.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 86d92f5465958752481269348d474414dccb1552 upstream.

Current driver has 240 (USB2.0) and 2048 (USB3.0) as max_sectors,
e.g., /sys/bus/scsi/devices/0:0:0:0/max_sectors

If data access times out, driver error handling will issue a port
reset.
Sometimes Samsung Fit (090C:1000) flash disk will not respond to
later Set Address or Get Descriptor command.

Adding this quirk to limit max_sectors to 64 sectors to avoid issue
occurring.

Signed-off-by: Jim Lin &lt;jilin@nvidia.com&gt;
Acked-by: Alan Stern &lt;stern@rowland.harvard.edu&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/1583158895-31342-1-git-send-email-jilin@nvidia.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>usb: uas: fix a plug &amp; unplug racing</title>
<updated>2020-02-28T14:39:12+00:00</updated>
<author>
<name>EJ Hsu</name>
<email>ejh@nvidia.com</email>
</author>
<published>2020-01-30T09:25:06+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=f41dc5155a4da609b5877583d1e870554b1fa46e'/>
<id>f41dc5155a4da609b5877583d1e870554b1fa46e</id>
<content type='text'>
commit 3e99862c05a9caa5a27969f41566b428696f5a9a upstream.

When a uas disk is plugged into an external hub, uas_probe()
will be called by the hub thread to do the probe. It will
first create a SCSI host and then do the scan for this host.
During the scan, it will probe the LUN using SCSI INQUERY command
which will be packed in the URB and submitted to uas disk.

There might be a chance that this external hub with uas disk
attached is unplugged during the scan. In this case, uas driver
will fail to submit the URB (due to the NOTATTACHED state of uas
device) and try to put this SCSI command back to request queue
waiting for next chance to run.

In normal case, this cycle will terminate when hub thread gets
disconnection event and calls into uas_disconnect() accordingly.
But in this case, uas_disconnect() will not be called because
hub thread of external hub gets stuck waiting for the completion
of this SCSI command. A deadlock happened.

In this fix, uas will call scsi_scan_host() asynchronously to
avoid the blocking of hub thread.

Signed-off-by: EJ Hsu &lt;ejh@nvidia.com&gt;
Acked-by: Oliver Neukum &lt;oneukum@suse.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/20200130092506.102760-1-ejh@nvidia.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 3e99862c05a9caa5a27969f41566b428696f5a9a upstream.

When a uas disk is plugged into an external hub, uas_probe()
will be called by the hub thread to do the probe. It will
first create a SCSI host and then do the scan for this host.
During the scan, it will probe the LUN using SCSI INQUERY command
which will be packed in the URB and submitted to uas disk.

There might be a chance that this external hub with uas disk
attached is unplugged during the scan. In this case, uas driver
will fail to submit the URB (due to the NOTATTACHED state of uas
device) and try to put this SCSI command back to request queue
waiting for next chance to run.

In normal case, this cycle will terminate when hub thread gets
disconnection event and calls into uas_disconnect() accordingly.
But in this case, uas_disconnect() will not be called because
hub thread of external hub gets stuck waiting for the completion
of this SCSI command. A deadlock happened.

In this fix, uas will call scsi_scan_host() asynchronously to
avoid the blocking of hub thread.

Signed-off-by: EJ Hsu &lt;ejh@nvidia.com&gt;
Acked-by: Oliver Neukum &lt;oneukum@suse.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/20200130092506.102760-1-ejh@nvidia.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>usb-storage: Disable UAS on JMicron SATA enclosure</title>
<updated>2020-02-05T13:03:36+00:00</updated>
<author>
<name>Laura Abbott</name>
<email>labbott@fedoraproject.org</email>
</author>
<published>2015-09-08T16:53:38+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=980494f6d53216a8f8ff97fd8c5a851e78ea95f9'/>
<id>980494f6d53216a8f8ff97fd8c5a851e78ea95f9</id>
<content type='text'>
[ Upstream commit bc3bdb12bbb3492067c8719011576370e959a2e6 ]

Steve Ellis reported incorrect block sizes and alignement
offsets with a SATA enclosure. Adding a quirk to disable
UAS fixes the problems.

Reported-by: Steven Ellis &lt;sellis@redhat.com&gt;
Cc: Pacho Ramos &lt;pachoramos@gmail.com&gt;
Signed-off-by: Laura Abbott &lt;labbott@fedoraproject.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
[ Upstream commit bc3bdb12bbb3492067c8719011576370e959a2e6 ]

Steve Ellis reported incorrect block sizes and alignement
offsets with a SATA enclosure. Adding a quirk to disable
UAS fixes the problems.

Reported-by: Steven Ellis &lt;sellis@redhat.com&gt;
Cc: Pacho Ramos &lt;pachoramos@gmail.com&gt;
Signed-off-by: Laura Abbott &lt;labbott@fedoraproject.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>UAS: Revert commit 3ae62a42090f ("UAS: fix alignment of scatter/gather segments")</title>
<updated>2019-11-06T11:09:18+00:00</updated>
<author>
<name>Alan Stern</name>
<email>stern@rowland.harvard.edu</email>
</author>
<published>2019-10-23T15:34:33+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=57d1b568570e9ee6c09e3caa859558ad08055e94'/>
<id>57d1b568570e9ee6c09e3caa859558ad08055e94</id>
<content type='text'>
commit 1186f86a71130a7635a20843e355bb880c7349b2 upstream.

Commit 3ae62a42090f ("UAS: fix alignment of scatter/gather segments"),
copying a similar commit for usb-storage, attempted to solve a problem
involving scatter-gather I/O and USB/IP by setting the
virt_boundary_mask for mass-storage devices.

However, it now turns out that the analogous change in usb-storage
interacted badly with commit 09324d32d2a0 ("block: force an unlimited
segment size on queues with a virt boundary"), which was added later.
A typical error message is:

	ehci-pci 0000:00:13.2: swiotlb buffer is full (sz: 327680 bytes),
	total 32768 (slots), used 97 (slots)

There is no longer any reason to keep the virt_boundary_mask setting
in the uas driver.  It was needed in the first place only for
handling devices with a block size smaller than the maxpacket size and
where the host controller was not capable of fully general
scatter-gather operation (that is, able to merge two SG segments into
a single USB packet).  But:

	High-speed or slower connections never use a bulk maxpacket
	value larger than 512;

	The SCSI layer does not handle block devices with a block size
	smaller than 512 bytes;

	All the host controllers capable of SuperSpeed operation can
	handle fully general SG;

	Since commit ea44d190764b ("usbip: Implement SG support to
	vhci-hcd and stub driver") was merged, the USB/IP driver can
	also handle SG.

Therefore all supported device/controller combinations should be okay
with no need for any special virt_boundary_mask.  So in order to head
off potential problems similar to those affecting usb-storage, this
patch reverts commit 3ae62a42090f.

Signed-off-by: Alan Stern &lt;stern@rowland.harvard.edu&gt;
CC: Oliver Neukum &lt;oneukum@suse.com&gt;
CC: &lt;stable@vger.kernel.org&gt;
Acked-by: Christoph Hellwig &lt;hch@lst.de&gt;
Fixes: 3ae62a42090f ("UAS: fix alignment of scatter/gather segments")
Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1910231132470.1878-100000@iolanthe.rowland.org
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 1186f86a71130a7635a20843e355bb880c7349b2 upstream.

Commit 3ae62a42090f ("UAS: fix alignment of scatter/gather segments"),
copying a similar commit for usb-storage, attempted to solve a problem
involving scatter-gather I/O and USB/IP by setting the
virt_boundary_mask for mass-storage devices.

However, it now turns out that the analogous change in usb-storage
interacted badly with commit 09324d32d2a0 ("block: force an unlimited
segment size on queues with a virt boundary"), which was added later.
A typical error message is:

	ehci-pci 0000:00:13.2: swiotlb buffer is full (sz: 327680 bytes),
	total 32768 (slots), used 97 (slots)

There is no longer any reason to keep the virt_boundary_mask setting
in the uas driver.  It was needed in the first place only for
handling devices with a block size smaller than the maxpacket size and
where the host controller was not capable of fully general
scatter-gather operation (that is, able to merge two SG segments into
a single USB packet).  But:

	High-speed or slower connections never use a bulk maxpacket
	value larger than 512;

	The SCSI layer does not handle block devices with a block size
	smaller than 512 bytes;

	All the host controllers capable of SuperSpeed operation can
	handle fully general SG;

	Since commit ea44d190764b ("usbip: Implement SG support to
	vhci-hcd and stub driver") was merged, the USB/IP driver can
	also handle SG.

Therefore all supported device/controller combinations should be okay
with no need for any special virt_boundary_mask.  So in order to head
off potential problems similar to those affecting usb-storage, this
patch reverts commit 3ae62a42090f.

Signed-off-by: Alan Stern &lt;stern@rowland.harvard.edu&gt;
CC: Oliver Neukum &lt;oneukum@suse.com&gt;
CC: &lt;stable@vger.kernel.org&gt;
Acked-by: Christoph Hellwig &lt;hch@lst.de&gt;
Fixes: 3ae62a42090f ("UAS: fix alignment of scatter/gather segments")
Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1910231132470.1878-100000@iolanthe.rowland.org
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>USB: storage: ums-realtek: Whitelist auto-delink support</title>
<updated>2019-09-06T08:18:16+00:00</updated>
<author>
<name>Kai-Heng Feng</name>
<email>kai.heng.feng@canonical.com</email>
</author>
<published>2019-08-27T17:34:50+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=4761474088761cd0705a80943dfafa0f723696d1'/>
<id>4761474088761cd0705a80943dfafa0f723696d1</id>
<content type='text'>
commit 1902a01e2bcc3abd7c9a18dc05e78c7ab4a53c54 upstream.

Auto-delink requires writing special registers to ums-realtek devices.
Unconditionally enable auto-delink may break newer devices.

So only enable auto-delink by default for the original three IDs,
0x0138, 0x0158 and 0x0159.

Realtek is working on a patch to properly support auto-delink for other
IDs.

BugLink: https://bugs.launchpad.net/bugs/1838886
Signed-off-by: Kai-Heng Feng &lt;kai.heng.feng@canonical.com&gt;
Acked-by: Alan Stern &lt;stern@rowland.harvard.edu&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/20190827173450.13572-2-kai.heng.feng@canonical.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 1902a01e2bcc3abd7c9a18dc05e78c7ab4a53c54 upstream.

Auto-delink requires writing special registers to ums-realtek devices.
Unconditionally enable auto-delink may break newer devices.

So only enable auto-delink by default for the original three IDs,
0x0138, 0x0158 and 0x0159.

Realtek is working on a patch to properly support auto-delink for other
IDs.

BugLink: https://bugs.launchpad.net/bugs/1838886
Signed-off-by: Kai-Heng Feng &lt;kai.heng.feng@canonical.com&gt;
Acked-by: Alan Stern &lt;stern@rowland.harvard.edu&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/20190827173450.13572-2-kai.heng.feng@canonical.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>USB: storage: ums-realtek: Update module parameter description for auto_delink_en</title>
<updated>2019-09-06T08:18:16+00:00</updated>
<author>
<name>Kai-Heng Feng</name>
<email>kai.heng.feng@canonical.com</email>
</author>
<published>2019-08-27T17:34:49+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=00087c6e434e8705d97ef8c0f796b573894e981b'/>
<id>00087c6e434e8705d97ef8c0f796b573894e981b</id>
<content type='text'>
commit f6445b6b2f2bb1745080af4a0926049e8bca2617 upstream.

The option named "auto_delink_en" is a bit misleading, as setting it to
false doesn't really disable auto-delink but let auto-delink be firmware
controlled.

Update the description to reflect the real usage of this parameter.

Signed-off-by: Kai-Heng Feng &lt;kai.heng.feng@canonical.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/20190827173450.13572-1-kai.heng.feng@canonical.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit f6445b6b2f2bb1745080af4a0926049e8bca2617 upstream.

The option named "auto_delink_en" is a bit misleading, as setting it to
false doesn't really disable auto-delink but let auto-delink be firmware
controlled.

Update the description to reflect the real usage of this parameter.

Signed-off-by: Kai-Heng Feng &lt;kai.heng.feng@canonical.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/20190827173450.13572-1-kai.heng.feng@canonical.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>usb-storage: Add new JMS567 revision to unusual_devs</title>
<updated>2019-09-06T08:18:16+00:00</updated>
<author>
<name>Henk van der Laan</name>
<email>opensource@henkvdlaan.com</email>
</author>
<published>2019-08-16T20:08:47+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=6f575b509cce81910666bdb0f4958cd01ab6d265'/>
<id>6f575b509cce81910666bdb0f4958cd01ab6d265</id>
<content type='text'>
commit 08d676d1685c2a29e4d0e1b0242324e564d4589e upstream.

Revision 0x0117 suffers from an identical issue to earlier revisions,
therefore it should be added to the quirks list.

Signed-off-by: Henk van der Laan &lt;opensource@henkvdlaan.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/20190816200847.21366-1-opensource@henkvdlaan.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 08d676d1685c2a29e4d0e1b0242324e564d4589e upstream.

Revision 0x0117 suffers from an identical issue to earlier revisions,
therefore it should be added to the quirks list.

Signed-off-by: Henk van der Laan &lt;opensource@henkvdlaan.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Link: https://lore.kernel.org/r/20190816200847.21366-1-opensource@henkvdlaan.com
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>USB: usb-storage: Add new ID to ums-realtek</title>
<updated>2019-06-22T06:18:24+00:00</updated>
<author>
<name>Kai-Heng Feng</name>
<email>kai.heng.feng@canonical.com</email>
</author>
<published>2019-06-03T16:20:49+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=f14747c88170ac97b31cd5150f6e23838561a599'/>
<id>f14747c88170ac97b31cd5150f6e23838561a599</id>
<content type='text'>
commit 1a6dd3fea131276a4fc44ae77b0f471b0b473577 upstream.

There is one more Realtek card reader requires ums-realtek to work
correctly.

Add the device ID to support it.

Signed-off-by: Kai-Heng Feng &lt;kai.heng.feng@canonical.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 1a6dd3fea131276a4fc44ae77b0f471b0b473577 upstream.

There is one more Realtek card reader requires ums-realtek to work
correctly.

Add the device ID to support it.

Signed-off-by: Kai-Heng Feng &lt;kai.heng.feng@canonical.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>UAS: fix alignment of scatter/gather segments</title>
<updated>2019-05-16T17:45:04+00:00</updated>
<author>
<name>Oliver Neukum</name>
<email>oneukum@suse.com</email>
</author>
<published>2019-04-30T10:21:45+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=dcb33fe3d9a68303bd506e069b579725452fa5c7'/>
<id>dcb33fe3d9a68303bd506e069b579725452fa5c7</id>
<content type='text'>
commit 3ae62a42090f1ed48e2313ed256a1182a85fb575 upstream.

This is the UAS version of

747668dbc061b3e62bc1982767a3a1f9815fcf0e
usb-storage: Set virt_boundary_mask to avoid SG overflows

We are not as likely to be vulnerable as storage, as it is unlikelier
that UAS is run over a controller without native support for SG,
but the issue exists.
The issue has been existing since the inception of the driver.

Fixes: 115bb1ffa54c ("USB: Add UAS driver")
Signed-off-by: Oliver Neukum &lt;oneukum@suse.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 3ae62a42090f1ed48e2313ed256a1182a85fb575 upstream.

This is the UAS version of

747668dbc061b3e62bc1982767a3a1f9815fcf0e
usb-storage: Set virt_boundary_mask to avoid SG overflows

We are not as likely to be vulnerable as storage, as it is unlikelier
that UAS is run over a controller without native support for SG,
but the issue exists.
The issue has been existing since the inception of the driver.

Fixes: 115bb1ffa54c ("USB: Add UAS driver")
Signed-off-by: Oliver Neukum &lt;oneukum@suse.com&gt;
Cc: stable &lt;stable@vger.kernel.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>USB: core: Fix bug caused by duplicate interface PM usage counter</title>
<updated>2019-05-16T17:45:00+00:00</updated>
<author>
<name>Alan Stern</name>
<email>stern@rowland.harvard.edu</email>
</author>
<published>2019-04-19T17:52:38+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=1b2b6db7765e73c9ae49dd6edb96db92b01d8048'/>
<id>1b2b6db7765e73c9ae49dd6edb96db92b01d8048</id>
<content type='text'>
commit c2b71462d294cf517a0bc6e4fd6424d7cee5596f upstream.

The syzkaller fuzzer reported a bug in the USB hub driver which turned
out to be caused by a negative runtime-PM usage counter.  This allowed
a hub to be runtime suspended at a time when the driver did not expect
it.  The symptom is a WARNING issued because the hub's status URB is
submitted while it is already active:

	URB 0000000031fb463e submitted while active
	WARNING: CPU: 0 PID: 2917 at drivers/usb/core/urb.c:363

The negative runtime-PM usage count was caused by an unfortunate
design decision made when runtime PM was first implemented for USB.
At that time, USB class drivers were allowed to unbind from their
interfaces without balancing the usage counter (i.e., leaving it with
a positive count).  The core code would take care of setting the
counter back to 0 before allowing another driver to bind to the
interface.

Later on when runtime PM was implemented for the entire kernel, the
opposite decision was made: Drivers were required to balance their
runtime-PM get and put calls.  In order to maintain backward
compatibility, however, the USB subsystem adapted to the new
implementation by keeping an independent usage counter for each
interface and using it to automatically adjust the normal usage
counter back to 0 whenever a driver was unbound.

This approach involves duplicating information, but what is worse, it
doesn't work properly in cases where a USB class driver delays
decrementing the usage counter until after the driver's disconnect()
routine has returned and the counter has been adjusted back to 0.
Doing so would cause the usage counter to become negative.  There's
even a warning about this in the USB power management documentation!

As it happens, this is exactly what the hub driver does.  The
kick_hub_wq() routine increments the runtime-PM usage counter, and the
corresponding decrement is carried out by hub_event() in the context
of the hub_wq work-queue thread.  This work routine may sometimes run
after the driver has been unbound from its interface, and when it does
it causes the usage counter to go negative.

It is not possible for hub_disconnect() to wait for a pending
hub_event() call to finish, because hub_disconnect() is called with
the device lock held and hub_event() acquires that lock.  The only
feasible fix is to reverse the original design decision: remove the
duplicate interface-specific usage counter and require USB drivers to
balance their runtime PM gets and puts.  As far as I know, all
existing drivers currently do this.

Signed-off-by: Alan Stern &lt;stern@rowland.harvard.edu&gt;
Reported-and-tested-by: syzbot+7634edaea4d0b341c625@syzkaller.appspotmail.com
CC: &lt;stable@vger.kernel.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

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<pre>
commit c2b71462d294cf517a0bc6e4fd6424d7cee5596f upstream.

The syzkaller fuzzer reported a bug in the USB hub driver which turned
out to be caused by a negative runtime-PM usage counter.  This allowed
a hub to be runtime suspended at a time when the driver did not expect
it.  The symptom is a WARNING issued because the hub's status URB is
submitted while it is already active:

	URB 0000000031fb463e submitted while active
	WARNING: CPU: 0 PID: 2917 at drivers/usb/core/urb.c:363

The negative runtime-PM usage count was caused by an unfortunate
design decision made when runtime PM was first implemented for USB.
At that time, USB class drivers were allowed to unbind from their
interfaces without balancing the usage counter (i.e., leaving it with
a positive count).  The core code would take care of setting the
counter back to 0 before allowing another driver to bind to the
interface.

Later on when runtime PM was implemented for the entire kernel, the
opposite decision was made: Drivers were required to balance their
runtime-PM get and put calls.  In order to maintain backward
compatibility, however, the USB subsystem adapted to the new
implementation by keeping an independent usage counter for each
interface and using it to automatically adjust the normal usage
counter back to 0 whenever a driver was unbound.

This approach involves duplicating information, but what is worse, it
doesn't work properly in cases where a USB class driver delays
decrementing the usage counter until after the driver's disconnect()
routine has returned and the counter has been adjusted back to 0.
Doing so would cause the usage counter to become negative.  There's
even a warning about this in the USB power management documentation!

As it happens, this is exactly what the hub driver does.  The
kick_hub_wq() routine increments the runtime-PM usage counter, and the
corresponding decrement is carried out by hub_event() in the context
of the hub_wq work-queue thread.  This work routine may sometimes run
after the driver has been unbound from its interface, and when it does
it causes the usage counter to go negative.

It is not possible for hub_disconnect() to wait for a pending
hub_event() call to finish, because hub_disconnect() is called with
the device lock held and hub_event() acquires that lock.  The only
feasible fix is to reverse the original design decision: remove the
duplicate interface-specific usage counter and require USB drivers to
balance their runtime PM gets and puts.  As far as I know, all
existing drivers currently do this.

Signed-off-by: Alan Stern &lt;stern@rowland.harvard.edu&gt;
Reported-and-tested-by: syzbot+7634edaea4d0b341c625@syzkaller.appspotmail.com
CC: &lt;stable@vger.kernel.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
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