On Fri, 20 Nov 2015, Ioan-Adrian Ratiu wrote: > The critical section protected by usbhid->lock in hid_ctrl() is too > big and because of this it causes a recursive deadlock. "Too big" means > the case statement and the call to hid_input_report() do not need to be > protected by the spinlock (no URB operations are done inside them). > > The deadlock happens because in certain rare cases drivers try to grab > the lock while handling the ctrl irq which grabs the lock before them > as described above. For example newer wacom tablets like 056a:033c try > to reschedule proximity reads from wacom_intuos_schedule_prox_event() > calling hid_hw_request() -> usbhid_request() -> usbhid_submit_report() > which tries to grab the usbhid lock already held by hid_ctrl(). > > There are two ways to get out of this deadlock: > 1. Make the drivers work "around" the ctrl critical region, in the > wacom case for ex. by delaying the scheduling of the proximity read > request itself to a workqueue. > 2. Shrink the critical region so the usbhid lock protects only the > instructions which modify usbhid state, calling hid_input_report() > with the spinlock unlocked, allowing the device driver to grab the > lock first, finish and then grab the lock afterwards in hid_ctrl(). > > This patch implements the 2nd solution. > > Signed-off-by: Ioan-Adrian Ratiu <adi@xxxxxxxxxx> Applied to for-4.5/core branch. Thanks, -- Jiri Kosina SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
