Commit ccb23d2d authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915/gt: Guard timeline pinning without relying on struct_mutex 



In preparation for removing struct_mutex from around context retirement,
we need to make timeline pinning and unpinning safe. Since multiple
engines/contexts can share a single timeline, we cannot rely on
borrowing the context mutex (otherwise we could state that the timeline
is only pinned/unpinned inside the context pin/unpin and so guarded by
it). However, we only perform a sequence of atomic operations inside the
timeline pin/unpin and the sequence of those operations is safe for a
concurrent unpin / pin, so we can relax the struct_mutex requirement.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarMatthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190815205709.24285-3-chris@chris-wilson.co.uk
parent 338aade9

drivers/gpu/drm/i915/gt/intel_timeline.c

+12 −15
Original line number Diff line number Diff line
@@ -211,9 +211,9 @@ int intel_timeline_init(struct intel_timeline *timeline, 
	void *vaddr;



	kref_init(&timeline->kref);

	atomic_set(&timeline->pin_count, 0);



	timeline->gt = gt;

	timeline->pin_count = 0;



	timeline->has_initial_breadcrumb = !hwsp;

	timeline->hwsp_cacheline = NULL;
@@ -280,7 +280,7 @@ void intel_timelines_init(struct drm_i915_private *i915) 


void intel_timeline_fini(struct intel_timeline *timeline)

{

	GEM_BUG_ON(timeline->pin_count);

	GEM_BUG_ON(atomic_read(&timeline->pin_count));

	GEM_BUG_ON(!list_empty(&timeline->requests));



	if (timeline->hwsp_cacheline)
@@ -314,33 +314,31 @@ int intel_timeline_pin(struct intel_timeline *tl) 
{

	int err;



	if (tl->pin_count++)

	if (atomic_add_unless(&tl->pin_count, 1, 0))

		return 0;

	GEM_BUG_ON(!tl->pin_count);

	GEM_BUG_ON(tl->active_count);



	err = i915_vma_pin(tl->hwsp_ggtt, 0, 0, PIN_GLOBAL | PIN_HIGH);

	if (err)

		goto unpin;

		return err;



	tl->hwsp_offset =

		i915_ggtt_offset(tl->hwsp_ggtt) +

		offset_in_page(tl->hwsp_offset);



	cacheline_acquire(tl->hwsp_cacheline);

	if (atomic_fetch_inc(&tl->pin_count)) {

		cacheline_release(tl->hwsp_cacheline);

		__i915_vma_unpin(tl->hwsp_ggtt);

	}



	return 0;



unpin:

	tl->pin_count = 0;

	return err;

}



void intel_timeline_enter(struct intel_timeline *tl)

{

	struct intel_gt_timelines *timelines = &tl->gt->timelines;



	GEM_BUG_ON(!tl->pin_count);

	GEM_BUG_ON(!atomic_read(&tl->pin_count));

	if (tl->active_count++)

		return;

	GEM_BUG_ON(!tl->active_count); /* overflow? */
@@ -372,7 +370,7 @@ void intel_timeline_exit(struct intel_timeline *tl) 


static u32 timeline_advance(struct intel_timeline *tl)

{

	GEM_BUG_ON(!tl->pin_count);

	GEM_BUG_ON(!atomic_read(&tl->pin_count));

	GEM_BUG_ON(tl->seqno & tl->has_initial_breadcrumb);



	return tl->seqno += 1 + tl->has_initial_breadcrumb;
@@ -523,11 +521,10 @@ int intel_timeline_read_hwsp(struct i915_request *from, 


void intel_timeline_unpin(struct intel_timeline *tl)

{

	GEM_BUG_ON(!tl->pin_count);

	if (--tl->pin_count)

	GEM_BUG_ON(!atomic_read(&tl->pin_count));

	if (!atomic_dec_and_test(&tl->pin_count))

		return;



	GEM_BUG_ON(tl->active_count);

	cacheline_release(tl->hwsp_cacheline);



	__i915_vma_unpin(tl->hwsp_ggtt);

drivers/gpu/drm/i915/gt/intel_timeline_types.h

+1 −1
Original line number Diff line number Diff line
@@ -41,7 +41,7 @@ struct intel_timeline { 
	 * but the pin_count is protected by a combination of serialisation

	 * from the intel_context caller plus internal atomicity.

	 */

	unsigned int pin_count;

	atomic_t pin_count;

	unsigned int active_count;



	const u32 *hwsp_seqno;

drivers/gpu/drm/i915/gt/mock_engine.c

+3 −3
Original line number Diff line number Diff line
@@ -34,13 +34,13 @@ 


static void mock_timeline_pin(struct intel_timeline *tl)

{

	tl->pin_count++;

	atomic_inc(&tl->pin_count);

}



static void mock_timeline_unpin(struct intel_timeline *tl)

{

	GEM_BUG_ON(!tl->pin_count);

	tl->pin_count--;

	GEM_BUG_ON(!atomic_read(&tl->pin_count));

	atomic_dec(&tl->pin_count);

}



static struct intel_ring *mock_ring(struct intel_engine_cs *engine)

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