[PATCH 6/7] drm/ttm: support using drm_exec during eviction v2

["Christian König" <ckoenig.leichtzumerken@xxxxxxxxx>]

Allow specifying a drm_exec object in TTMs operation context which is
used to lock objects during eviction.

This allows to handle deadlocks much more gracefully and with that
avoid returning -ENOMEM on heavily contended domains.

v2: rebased on top of Thomas work

TODO: This still doesn't handle BOs which are about to be torn down
correctly.

Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
 drivers/gpu/drm/ttm/ttm_bo_util.c | 45 +++++++++++++++++++++++++------
 drivers/gpu/drm/ttm/ttm_bo_util.h |  2 ++
 include/drm/ttm/ttm_bo.h          |  3 +++
 3 files changed, 42 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index 7a4bc7e9950b..850e329ab5a5 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -36,6 +36,7 @@
 #include <drm/ttm/ttm_tt.h>
 
 #include <drm/drm_cache.h>
+#include <drm/drm_exec.h>
 
 #include "ttm_bo_util.h"
 
@@ -776,15 +777,22 @@ static bool ttm_lru_walk_trylock(struct ttm_lru_walk *walk,
 {
 	struct ttm_operation_ctx *ctx = walk->ctx;
 
+	walk->needs_drop = false;
 	walk->needs_unlock = false;
 
-	if (dma_resv_trylock(bo->base.resv)) {
-		walk->needs_unlock = true;
+	if (bo->base.resv == ctx->resv && ctx->allow_res_evict) {
+		dma_resv_assert_held(bo->base.resv);
 		return true;
 	}
 
-	if (bo->base.resv == ctx->resv && ctx->allow_res_evict) {
-		dma_resv_assert_held(bo->base.resv);
+	if (walk->ctx->exec) {
+		if (drm_exec_trylock_obj(walk->ctx->exec, &bo->base)) {
+			walk->needs_drop = true;
+			return true;
+		}
+
+	} else if (dma_resv_trylock(bo->base.resv)) {
+		walk->needs_unlock = true;
 		return true;
 	}
 
@@ -797,7 +805,9 @@ static int ttm_lru_walk_ticketlock(struct ttm_lru_walk *walk,
 	struct dma_resv *resv = bo->base.resv;
 	int ret;
 
-	if (walk->ctx->interruptible)
+	if (walk->ctx->exec)
+		ret = drm_exec_lock_obj(walk->ctx->exec, &bo->base);
+	else if (walk->ctx->interruptible)
 		ret = dma_resv_lock_interruptible(resv, walk->ticket);
 	else
 		ret = dma_resv_lock(resv, walk->ticket);
@@ -811,7 +821,8 @@ static int ttm_lru_walk_ticketlock(struct ttm_lru_walk *walk,
 		 * trylocking for this walk.
 		 */
 		walk->ticket = NULL;
-	} else if (ret == -EDEADLK) {
+
+	} else if (!walk->ctx->exec && ret == -EDEADLK) {
 		/* Caller needs to exit the ww transaction. */
 		ret = -ENOSPC;
 	}
@@ -822,7 +833,15 @@ static int ttm_lru_walk_ticketlock(struct ttm_lru_walk *walk,
 static void ttm_lru_walk_unlock(struct ttm_lru_walk *walk,
 				struct ttm_buffer_object *bo)
 {
-	if (walk->needs_unlock)
+	if (walk->needs_drop)
+		drm_exec_drop_trylocked_obj(walk->ctx->exec, &bo->base);
+
+	if (!walk->needs_unlock)
+		return;
+
+	if (walk->ctx->exec)
+		drm_exec_unlock_obj(walk->ctx->exec, &bo->base);
+	else
 		dma_resv_unlock(bo->base.resv);
 }
 
@@ -891,8 +910,18 @@ s64 ttm_lru_walk_for_evict(struct ttm_lru_walk *walk, struct ttm_device *bdev,
 		spin_unlock(&bdev->lru_lock);
 
 		lret = 0;
-		if (!bo_locked)
+		if (!bo_locked) {
 			lret = ttm_lru_walk_ticketlock(walk, bo);
+		} else if (walk->ctx->exec && !bo->deleted) {
+			lret = drm_exec_keep_trylocked_obj(walk->ctx->exec,
+							   &bo->base);
+			if (!lret) {
+				walk->needs_drop = false;
+				walk->needs_unlock = true;
+			}
+		} else {
+			lret = 0;
+		}
 
 		/*
 		 * Note that in between the release of the lru lock and the
diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.h b/drivers/gpu/drm/ttm/ttm_bo_util.h
index c653e16ccb76..5e1bb156837f 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.h
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.h
@@ -59,6 +59,8 @@ struct ttm_lru_walk {
 	struct ww_acquire_ctx *ticket;
 	/** @tryock_only: Only use trylock for locking. */
 	bool trylock_only;
+	/** @needs_drop: If the current BO needs a drm_exec trylock drop */
+	bool needs_drop;
 	/** @needs_unlock: If the current BO needs unlocking */
 	bool needs_unlock;
 };
diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
index 5f7c967222a2..5bee917e01e2 100644
--- a/include/drm/ttm/ttm_bo.h
+++ b/include/drm/ttm/ttm_bo.h
@@ -180,6 +180,8 @@ struct ttm_bo_kmap_obj {
  * faults. Should only be used by TTM internally.
  * @resv: Reservation object to allow reserved evictions with.
  * @bytes_moved: Statistics on how many bytes have been moved.
+ * @exec: optional drm_exec object to use for locking BOs and tracking which are
+ * locked.
  *
  * Context for TTM operations like changing buffer placement or general memory
  * allocation.
@@ -192,6 +194,7 @@ struct ttm_operation_ctx {
 	bool force_alloc;
 	struct dma_resv *resv;
 	uint64_t bytes_moved;
+	struct drm_exec *exec;
 };
 
 /**
-- 
2.34.1