Re: [PATCH] drm/ttm: fix deref of bo->ttm without holding the lock v2

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

On 5/28/21 3:00 PM, Christian König wrote:
> We need to grab the resv lock first before doing that check.
>
> v2 (chk): simplify the change for -fixes
>
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Hmm, OK, but this doesn't fix the swapped-bo-not-on-lru and unpopulating 
from swap_notify issues. Are you planning a follow up patch for those?

Thanks,

Thomas

> ---
>   drivers/gpu/drm/ttm/ttm_bo.c     | 5 ++++-
>   drivers/gpu/drm/ttm/ttm_device.c | 8 +-------
>   2 files changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index cfd0b9292397..ebcffe794adb 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -1172,7 +1172,10 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
>   	if (!ttm_bo_evict_swapout_allowable(bo, ctx, &locked, NULL))
>   		return -EBUSY;
>   
> -	if (!ttm_bo_get_unless_zero(bo)) {
> +	if (!bo->ttm || !ttm_tt_is_populated(bo->ttm) ||
> +	    bo->ttm->page_flags & TTM_PAGE_FLAG_SG ||
> +	    bo->ttm->page_flags & TTM_PAGE_FLAG_SWAPPED ||
> +	    !ttm_bo_get_unless_zero(bo)) {
>   		if (locked)
>   			dma_resv_unlock(bo->base.resv);
>   		return -EBUSY;
> diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> index a1dcf7d55c90..3d9c62b93e29 100644
> --- a/drivers/gpu/drm/ttm/ttm_device.c
> +++ b/drivers/gpu/drm/ttm/ttm_device.c
> @@ -143,14 +143,8 @@ int ttm_device_swapout(struct ttm_device *bdev, struct ttm_operation_ctx *ctx,
>   
>   		for (j = 0; j < TTM_MAX_BO_PRIORITY; ++j) {
>   			list_for_each_entry(bo, &man->lru[j], lru) {
> -				uint32_t num_pages;
> +				uint32_t num_pages = PFN_UP(bo->base.size);
>   
> -				if (!bo->ttm || !ttm_tt_is_populated(bo->ttm) ||
> -				    bo->ttm->page_flags & TTM_PAGE_FLAG_SG ||
> -				    bo->ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)
> -					continue;
> -
> -				num_pages = bo->ttm->num_pages;
>   				ret = ttm_bo_swapout(bo, ctx, gfp_flags);
>   				/* ttm_bo_swapout has dropped the lru_lock */
>   				if (!ret)