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    SubjectRe: [PATCH] hid: usbhid: hid-core: fix recursive deadlock
    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



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