On Thu, 23 May 2024 12:32:17 +0100
Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx> wrote:
> When Panfrost must pin an object that is being prepared a dma-buf
> attachment for on behalf of another driver, the core drm gem object pinning
> code already takes a lock on the object's dma reservation.
>
> However, Panfrost GEM object's pinning callback would eventually try taking
> the lock on the same dma reservation when delegating pinning of the object
> onto the shmem subsystem, which led to a deadlock.
>
> This can be shown by enabling CONFIG_DEBUG_WW_MUTEX_SLOWPATH, which throws
> the following recursive locking situation:
>
> weston/3440 is trying to acquire lock:
> ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_shmem_pin+0x34/0xb8 [drm_shmem_helper]
> but task is already holding lock:
> ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_pin+0x2c/0x80 [drm]
>
> Fix it by replacing drm_gem_shmem_pin with its locked version, as the lock
> had already been taken by drm_gem_pin().
>
> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Cc: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
> Cc: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> Cc: Steven Price <steven.price@xxxxxxx>
> Fixes: a78027847226 ("drm/gem: Acquire reservation lock in drm_gem_{pin/unpin}()")
> Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/panfrost/panfrost_gem.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index d47b40b82b0b..8e0ff3efede7 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -192,7 +192,7 @@ static int panfrost_gem_pin(struct drm_gem_object *obj)
> if (bo->is_heap)
> return -EINVAL;
>
> - return drm_gem_shmem_pin(&bo->base);
> + return drm_gem_shmem_pin_locked(&bo->base);
> }
>
> static enum drm_gem_object_status panfrost_gem_status(struct drm_gem_object *obj)
