Hi Jiri, On Tue, Dec 1, 2015 at 8:36 AM, Jiri Kosina <jikos@xxxxxxxxxx> wrote: > 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, Since wacom_intuos_schedule_prox_event() was introduced on March 5, 2015, the call was first used in kernel 3.19. Shouldn't we back-port this patch to other stable versions? Thank you. Ping -- 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
