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The USB stack provides a mechanism for drivers to request an asynchronous device reset (usb_queue_reset_device()). The mechanism uses a work item (reset_ws) embedded in the usb_interface structure used by the driver, and the reset is carried out by a work queue routine. The asynchronous reset can race with driver unbinding. When this happens, we try to cancel the queued reset before unbinding the driver, on the theory that the driver won't care about any resets once it is unbound. However, thanks to the fact that lockdep now tracks work queue accesses, this can provoke a lockdep warning in situations where the device reset causes another interface's driver to be unbound; see http://marc.info/?l=linux-usb&m=141893165203776&w=2 for an example. The reason is that the work routine for reset_ws in one interface calls cancel_queued_work() for the reset_ws in another interface. Lockdep thinks this might lead to a work routine trying to cancel itself. The simplest solution is not to cancel queued resets when unbinding drivers. This means we now need to acquire a reference to the usb_interface when queuing a reset_ws work item and to drop the reference when the work routine finishes. We also need to make sure that the usb_interface structure doesn't outlive its parent usb_device; this means acquiring and dropping a reference when the interface is created and destroyed. In addition, cancelling a queued reset can fail (if the device is in the middle of an earlier reset), and this can cause usb_reset_device() to try to rebind an interface that has been deallocated (see http://marc.info/?l=linux-usb&m=142175717016628&w=2 for details). Acquiring the extra references prevents this failure. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Reported-by: Russell King - ARM Linux <linux@arm.linux.org.uk> Reported-by: Olivier Sobrie <olivier@sobrie.be> Tested-by: Olivier Sobrie <olivier@sobrie.be> Cc: stable <stable@vger.kernel.org> # 3.19 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| linux | ||
| math-emu | ||
| media | ||
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| misc | ||
| net | ||
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| soc | ||
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| target | ||
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| uapi | ||
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| Kbuild | ||