Re: [PATCH 09/10] drm/ttm: support using drm_exec during eviction v4

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Fri, 2026-07-03 at 18:31 +0200, Natalie Vock wrote:
> From: Christian König <christian.koenig@amd.com>
> 
> 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
> v3: rebased again
> v4: rebased, fixed locks of already-reserved buffers being dropped
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Signed-off-by: Natalie Vock <natalie.vock@gmx.de>
> ---
>  drivers/gpu/drm/ttm/ttm_bo_util.c | 30 ++++++++++++++++++++++-------
> -
>  include/drm/ttm/ttm_bo.h          |  5 +++++
>  2 files changed, 27 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c
> b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index a53b25e8c2967..96699532817c2 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -38,6 +38,7 @@
>  #include <drm/ttm/ttm_tt.h>
>  
>  #include <drm/drm_cache.h>
> +#include <drm/drm_exec.h>
>  
>  #include "ttm_bo_internal.h"
>  
> @@ -837,6 +838,8 @@ static bool ttm_lru_walk_trylock(struct
> ttm_bo_lru_cursor *curs,
>  	struct ttm_operation_ctx *ctx = curs->arg->ctx;
>  
>  	curs->needs_unlock = false;
> +	if (ctx->exec)
> +		return false;

The first passes of eviction typically trylocks, and no_wait_gpu also
skips sleeping locks since they can be held why waiting for fences.
Otoh we could check that no_wait_gpu and exec is mutually exclusive.

But I think trylocking should be tried before exec locking to also
avoid costly rollbacks, in line with mutex lock stealing.

>  
>  	if (dma_resv_trylock(bo->base.resv)) {
>  		curs->needs_unlock = true;
> @@ -857,7 +860,9 @@ static int ttm_lru_walk_ticketlock(struct
> ttm_bo_lru_cursor *curs,
>  	struct ttm_lru_walk_arg *arg = curs->arg;
>  	int ret;
>  
> -	if (arg->ctx->interruptible)
> +	if (arg->ctx->exec)
> +		ret = drm_exec_lock_obj_report_dup(arg->ctx->exec,
> &bo->base);
> +	else if (arg->ctx->interruptible)
>  		ret = dma_resv_lock_interruptible(bo->base.resv,
> arg->ticket);
>  	else
>  		ret = dma_resv_lock(bo->base.resv, arg->ticket);
> @@ -871,7 +876,11 @@ static int ttm_lru_walk_ticketlock(struct
> ttm_bo_lru_cursor *curs,
>  		 * trylocking for this walk.
>  		 */
>  		arg->ticket = NULL;
> -	} else if (ret == -EDEADLK) {
> +
> +	} else if (arg->ctx->exec && arg->ctx->allow_res_evict &&
> +		   ret == -EALREADY) {
> +		ret = 0;
> +	} else if (!arg->ctx->exec && ret == -EDEADLK) {
>  		/* Caller needs to exit the ww transaction. */
>  		ret = -ENOSPC;
>  	}
> @@ -937,12 +946,17 @@ static void ttm_bo_lru_cursor_cleanup_bo(struct
> ttm_bo_lru_cursor *curs)
>  {
>  	struct ttm_buffer_object *bo = curs->bo;
>  
> -	if (bo) {
> -		if (curs->needs_unlock)
> +	if (!bo)
> +		return;
> +
> +	if (curs->needs_unlock) {
> +		if (curs->arg->ctx->exec)
> +			drm_exec_unlock_obj(curs->arg->ctx->exec,
> &bo->base);

Unlocking after each locks sort of defeats the purpose of ww locking,
since it can't guarantee forward progress, but I guess will work as an
initial attempt.

Thanks,
Thomas


> +		else
>  			dma_resv_unlock(bo->base.resv);
> -		ttm_bo_put(bo);
> -		curs->bo = NULL;
>  	}
> +	ttm_bo_put(bo);
> +	curs->bo = NULL;
>  }
>  
>  /**
> @@ -1016,8 +1030,8 @@ __ttm_bo_lru_cursor_next(struct
> ttm_bo_lru_cursor *curs)
>  		if (ttm_lru_walk_trylock(curs, bo)) {
>  			bo_locked = true;
>  
> -		} else if (!arg->ticket || arg->ctx->no_wait_gpu ||
> -			   arg->trylock_only) {
> +		} else if ((!arg->ticket || arg->ctx->no_wait_gpu ||
> +			    arg->trylock_only) && !arg->ctx->exec) {
>  			spin_unlock(lru_lock);
>  			ttm_bo_put(bo);
>  			spin_lock(lru_lock);
> diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
> index a4060e44d23d0..156444b5e85d8 100644
> --- a/include/drm/ttm/ttm_bo.h
> +++ b/include/drm/ttm/ttm_bo.h
> @@ -187,6 +187,11 @@ struct ttm_operation_ctx {
>  	 * @bytes_moved: Statistics on how many bytes have been
> moved.
>  	 */
>  	uint64_t bytes_moved;
> +	/**
> +	 * @exec: optional drm_exec object to use for locking BOs
> and
> +	 * tracking which are locked.
> +	 */
> +	struct drm_exec *exec;
>  };
>  
>  /**