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Commit 6c12db90f19727c76990e7f4801c67a148b30111 introduced a bug for control transfers. The patch was supposed to change when the link TRBs at the end of each ring segment were given to the hardware. If a transfer descriptor (TD) ended just before the link TRB, the code wouldn't give back the link TRB to the hardware; instead it would be given back in prepare_ring() just before the next TD was enqueued at the top of the ring. Unfortunately, the code relied on checking the chain bit of the TRB to determine whether the TD ended just before the link TRB. It assumed that the ring enqueuing code would call prepare_ring() before enqueuing the next TD. However, control transfers are made of multiple TDs, and prepare_ring() is only called once before enqueuing two or three TDs. If the first or second TD of the control transfer ended just before the link TRB, then the code in inc_enq() would not move the enqueue pointer past the link TRB, and the link TRB would get overwritten. This would cause the xHCI driver to start writing to memory past the ring segment, and eventually the system would crash or hang. The fix is to add a flag to inc_enq() that says whether the caller will enqueue more TDs before calling prepare_ring(). If the chain bit is cleared (meaning this is the last TRB in a TD), and the caller will not enqueue more TDs, then we defer giving back the link TRB. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Cc: stable <stable@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("khubd").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.