On Tue, Jul 21, 2020 at 09:32:36AM +0200, Christian König wrote:
> Nouveau is the only user of this functionality and evicting io space
> on -EAGAIN is really a misuse of the return code.
>
> Instead switch to using -ENOSPC here which makes much more sense and
> simplifies the code.
>
> Signed-off-by: Christian König <christian.koenig@xxxxxxx>
Going from EAGAIN to something else could unbreak something that's held
together as a almost livelock restarting ioctls or whatever. So I looked
for that a bit:
- mmap path seems fine, all errors from the io_reserve stuff here get
remapped to sigbus
- but everywhere else we just pass down the errno it seems, and nouveau
has a bunch of kmaps all around (gpu relocs on pre-nv50 is probably the
big one, if we ignore the memcpy bo move fallback). I haven't found
anything that indicates those chips don't have the ioremapping hw, so
there's some risk I think. Otoh I also don't see anything that would
unbreak the lifelook, so feels minimally.
With that impact to pushbuf ioctl documented in the commit message somehow
this is Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
> drivers/gpu/drm/nouveau/nouveau_bo.c | 2 --
> drivers/gpu/drm/ttm/ttm_bo_util.c | 4 ++--
> 2 files changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index 61355cfb7335..a48652826f67 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -1505,8 +1505,6 @@ nouveau_ttm_io_mem_reserve(struct ttm_bo_device *bdev, struct ttm_mem_reg *reg)
> if (ret != 1) {
> if (WARN_ON(ret == 0))
> return -EINVAL;
> - if (ret == -ENOSPC)
> - return -EAGAIN;
> return ret;
> }
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index 5e0f3a9caedc..7d2c50fef456 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -116,7 +116,7 @@ static int ttm_mem_io_evict(struct ttm_mem_type_manager *man)
> struct ttm_buffer_object *bo;
>
> if (!man->use_io_reserve_lru || list_empty(&man->io_reserve_lru))
> - return -EAGAIN;
> + return -ENOSPC;
>
> bo = list_first_entry(&man->io_reserve_lru,
> struct ttm_buffer_object,
> @@ -143,7 +143,7 @@ int ttm_mem_io_reserve(struct ttm_bo_device *bdev,
> mem->bus.io_reserved_count++ == 0) {
> retry:
> ret = bdev->driver->io_mem_reserve(bdev, mem);
> - if (ret == -EAGAIN) {
> + if (ret == -ENOSPC) {
> ret = ttm_mem_io_evict(man);
> if (ret == 0)
> goto retry;
> --
> 2.17.1
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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