[Bug 111905] [CI][BAT] igt at i915_selftest@live_hangcheck - incomplete - BUG: kernel NULL pointer dereference, address: 0000000000000028

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111905

--- Comment #5 from Chris Wilson <chris at chris-wilson.co.uk> ---
commit c949ae431467764277cdd88d7c26ff963a9db40a
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Wed Oct 9 11:09:54 2019 +0100

    drm/i915/execlists: Protect peeking at execlists->active

    Now that we dropped the engine->active.lock serialisation from around
    process_csb(), direct submission can run concurrently to the interrupt
    handler. As such execlists->active may be advanced as we dequeue,
    dropping the reference to the request. We need to employ our RCU request
    protection to ensure that the request is not freed too early.

    Fixes: df403069029d ("drm/i915/execlists: Lift process_csb() out of the
irq-off spinlock")
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
    Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20191009100955.21477-1-chris@chris-wilson.co.uk

is a vaguely related patch. It shouldn't impact this path along reset, but
maybe it provides a hint?

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