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commit c2b71462d2 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 <stern@rowland.harvard.edu>
Reported-and-tested-by: syzbot+7634edaea4d0b341c625@syzkaller.appspotmail.com
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Felipe writes:
usb: changes for v4.13 merge window
This time around we have a total of 57 non-merge commits. A list of
most important changes follows:
- Improvements to dwc3 tracing interface
- Initial dual-role support for dwc3
- Improvements to how we handle DMA resources in dwc3
- A new f_uac1 implementation which much more flexible
- Removal of AVR32 bits
- Improvements to f_mass_storage driver
The contents of proc_usb_info.txt complements what's there at
driver-api usb book. Yet, it is outdated, as it still refers
to the USB character devices as usbfs.
So, move the contents to usb.rst, adjusting it to point to
the right places.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
There's no usbfs anymore. The old features are now either
exported to /dev/bus/usb or via debugfs.
Update documentation accordingly, pointing to the new
places where the character devices and usb/devices are
now placed.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
As some USB documentation files got moved, adjust their
cross-references to their new place.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The URB doc describes the Kernel mechanism that do USB transfers.
While the functions are already described at urb.h, there are a
number of concepts and theory that are important for USB driver
developers.
Convert it to ReST and use C ref links to point to the places
at usb.h where each function and struct is located.
A few of those descriptions were incomplete. While here, update
to reflect the current API status.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This file is actually quite complex, and required several
manual handwork:
- add a title for the document;
- use the right tags for monospaced fonts;
- use c references where needed;
- adjust cross-reference to writing_usb_driver.rst
- hightlight cross-referenced lines.
With regards to C code snippet line highlights, the better would be
to use :linenos: for the C code snippets that are referenced by
the line number. However, at least with Sphinx 1.4.9, enabling
it cause the line number to be misaligned with the code,
making it even more confusing. So, instead, let's use
:emphasize-lines: tag to mark the lines that are referenced
at the text.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The pandoc conversion is not perfect. Do handwork in order to:
- add a title to this chapter;
- adjust function and struct references;
- use monospaced fonts for C code names;
- some other minor adjustments to make it better to read in
text mode and in html.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The pandoc conversion is not perfect. Do handwork in order to:
- add a title to this chapter;
- use the proper warning and note markups;
- use kernel-doc to include Kernel header and c files;
- remove legacy notes with regards to DocBook;
- some other minor adjustments to make it better to read in
text mode and in html.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
- use the proper warning and note markups;
- add references for parts of the document that will be
cross-referenced on other USB docs;
- some minor adjustments to make it better to read in
text mode and in html.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
As we're moving out of DocBook, let's convert the remaining
USB docbooks to ReST.
The transformation itself on this patch is a no-brainer
conversion using pandoc via this script:
Documentation/sphinx/tmplcvt
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
