linux-kernel - Re: [PATCH] drm/i915: Fix i915_gem_wait_for_idle oops due to active

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Date:   Thu, 20 Dec 2018 08:35:54 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     airlied@...ux.ie, alek.du@...el.com, bin.yang@...el.com,
        daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, jani.nikula@...ux.intel.com,
        jani.saarinen@...el.com, joonas.lahtinen@...ux.intel.com,
        linux-kernel@...r.kernel.org, rodrigo.vivi@...el.com
Subject: Re: [PATCH] drm/i915: Fix i915_gem_wait_for_idle oops due to active_requests
 check

Quoting Bin Yang (2018-12-20 08:01:35)
> Normally, i915_request_alloc() and i915_request_add() will be called
> in sequence with drm.struct_mutex locked. But in
> intel_vgpu_create_workload(), it will pre-allocate the request and
> call i915_request_add() in the workload thread for performance
> optimization. The above issue will be triggered.

That's your bug. It's not normally, it's a strict requirement that the
struct_mutex (request generation mutex) be held over the course of
generating the request.
-Chris