8963c487a8
This patch (as154) fixes a self-deadlock that occurs when userspace
writes to the bConfigurationValue sysfs attribute for a hub with
children. The task tries to lock the bandwidth_mutex at a time when
it already owns the lock:
The attribute's method calls usb_set_configuration(),
which calls usb_disable_device() with the bandwidth_mutex
held.
usb_disable_device() unregisters the existing interfaces,
which causes the hub driver to be unbound.
The hub_disconnect() routine calls hub_quiesce(), which
calls usb_disconnect() for each of the hub's children.
usb_disconnect() attempts to acquire the bandwidth_mutex
around a call to usb_disable_device().
The solution is to make usb_disable_device() acquire the mutex for
itself instead of requiring the caller to hold it. Then the mutex can
cover only the bandwidth deallocation operation and not the region
where the interfaces are unregistered.
This has the potential to change system behavior slightly when a
config change races with another config or altsetting change. Some of
the bandwidth released from the old config might get claimed by the
other config or altsetting, make it impossible to restore the old
config in case of a failure. But since we don't try to recover from
config-change failures anyway, this doesn't matter.
[This should be marked for stable kernels that contain the commit
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.. | ||
atm | ||
c67x00 | ||
class | ||
core | ||
dwc3 | ||
early | ||
gadget | ||
host | ||
image | ||
misc | ||
mon | ||
musb | ||
otg | ||
renesas_usbhs | ||
serial | ||
storage | ||
wusbcore | ||
Kconfig | ||
Makefile | ||
README | ||
usb-common.c | ||
usb-skeleton.c |
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.