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Commit b3a38998 authored by Nick Hoath's avatar Nick Hoath Committed by Jani Nikula
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drm/i915: Fix a use after free, and unbalanced refcounting 

When converting from implicitly tracked execlist queue items to ref counted
requests, not all frees of requests were replaced with unrefs, and extraneous
refs/unrefs of contexts were added.
Correct the unbalanced refcount & replace the frees.
Remove a noisy warning when hitting the request creation path.

drm_i915_gem_request and intel_context are both kref reference counted
structures. Upon allocation, drm_i915_gem_request's ref count should be
bumped using kref_init. When a context is assigned to the request,
the context's reference count should be bumped using i915_gem_context_reference.
i915_gem_request_reference will reduce the context reference count when
the request is freed.

Problem introduced in
commit 6d3d8274
Author:     Nick Hoath <nicholas.hoath@intel.com>
AuthorDate: Thu Jan 15 13:10:39 2015 +0000

     drm/i915: Subsume intel_ctx_submit_request in to drm_i915_gem_request

v2: Added comments explaining how the ctx pointer and the request object should
be ref-counted. Removed noisy warning.

v3: Cleaned up the language used in the commit & the header
description (Thanks David Gordon)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88652


Signed-off-by: default avatarNick Hoath <nicholas.hoath@intel.com>
Reviewed-by: default avatarThomas Daniel <thomas.daniel@intel.com>
Reviewed-by: default avatarDaniel Vetter <daniel@ffwll.ch>
Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
parent cf6f0af9

drivers/gpu/drm/i915/i915_drv.h

+13 −1
Original line number Diff line number Diff line
@@ -2114,6 +2114,9 @@ void i915_gem_track_fb(struct drm_i915_gem_object *old, 
 * number comparisons on buffer last_read|write_seqno. It also allows an

 * emission time to be associated with the request for tracking how far ahead

 * of the GPU the submission is.

 *

 * The requests are reference counted, so upon creation they should have an

 * initial reference taken using kref_init

 */

struct drm_i915_gem_request {

	struct kref ref;
@@ -2137,7 +2140,16 @@ struct drm_i915_gem_request { 
	/** Position in the ringbuffer of the end of the whole request */

	u32 tail;



	/** Context related to this request */

	/**

	 * Context related to this request

	 * Contexts are refcounted, so when this request is associated with a

	 * context, we must increment the context's refcount, to guarantee that

	 * it persists while any request is linked to it. Requests themselves

	 * are also refcounted, so the request will only be freed when the last

	 * reference to it is dismissed, and the code in

	 * i915_gem_request_free() will then decrement the refcount on the

	 * context.

	 */

	struct intel_context *ctx;



	/** Batch buffer related to this request if any */

drivers/gpu/drm/i915/i915_gem.c

+1 −2
Original line number Diff line number Diff line
@@ -2659,8 +2659,7 @@ static void i915_gem_reset_ring_cleanup(struct drm_i915_private *dev_priv, 
		if (submit_req->ctx != ring->default_context)

			intel_lr_context_unpin(ring, submit_req->ctx);



		i915_gem_context_unreference(submit_req->ctx);

		kfree(submit_req);

		i915_gem_request_unreference(submit_req);

	}



	/*

drivers/gpu/drm/i915/intel_lrc.c

+4 −4
Original line number Diff line number Diff line
@@ -503,18 +503,19 @@ static int execlists_context_queue(struct intel_engine_cs *ring, 
		 * If there isn't a request associated with this submission,

		 * create one as a temporary holder.

		 */

		WARN(1, "execlist context submission without request");

		request = kzalloc(sizeof(*request), GFP_KERNEL);

		if (request == NULL)

			return -ENOMEM;

		request->ring = ring;

		request->ctx = to;

		kref_init(&request->ref);

		request->uniq = dev_priv->request_uniq++;

		i915_gem_context_reference(request->ctx);

	} else {

		i915_gem_request_reference(request);

		WARN_ON(to != request->ctx);

	}

	request->tail = tail;

	i915_gem_request_reference(request);

	i915_gem_context_reference(request->ctx);



	intel_runtime_pm_get(dev_priv);
@@ -731,7 +732,6 @@ void intel_execlists_retire_requests(struct intel_engine_cs *ring) 
		if (ctx_obj && (ctx != ring->default_context))

			intel_lr_context_unpin(ring, ctx);

		intel_runtime_pm_put(dev_priv);

		i915_gem_context_unreference(ctx);

		list_del(&req->execlist_link);

		i915_gem_request_unreference(req);

	}