We cannot let the request be retired and freed while we are trying to
dump it during error capture. It is not sufficient just to grab a
reference to the request, as during retirement we may free the ring
which we are also dumping. So take the engine lock to prevent retiring
and freeing of the request.
Reported-by: NAlex Shumsky <alexthreed@gmail.com>
Fixes: 83c31783 ("drm/i915: Dump the ringbuffer of the active request for debugging")
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Alex Shumsky <alexthreed@gmail.com>
Reviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190715080946.15593-6-chris@chris-wilson.co.uk
(cherry picked from commit cfe7288c)
Signed-off-by: NJani Nikula <jani.nikula@intel.com>