On Wed, 18 Nov 2015, Ioan-Adrian Ratiu wrote: > The critical section protected by usbhid->lock in hid_ctrl() is too > big and in rare cases causes a recursive deadlock because of its call > to hid_input_report(). > > This deadlock reproduces on newer wacom tablets like 056a:033c because > the wacom driver in its irq handler ends up calling hid_hw_request() > from wacom_intuos_schedule_prox_event() in wacom_wac.c. What this means > is that it submits a report to reschedule a proximity read through a > sync ctrl call which grabs the lock in hid_ctrl(struct urb *urb) > before calling hid_input_report(). When the irq kicks in on the same > cpu, it also tries to grab the lock resulting in a recursive deadlock. > > The proper fix is to shrink the critical section in hid_ctrl() to > protect only the instructions which modify usbhid, thus move the lock > after the hid_input_report() call and the deadlock dissapears. I think the proper fix actually is to spin_lock_irqsave() in hid_ctrl(), isn't it? -- 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
