Re: [resend PATCH] drm/ttm: Fix a deadlock if the target BO is not idle during swap

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Sep 07, 2021 at 08:22:20AM +0200, Christian König wrote:
> Added a Fixes tag and pushed this to drm-misc-fixes.

We're in the merge window, this should have been drm-misc-next-fixes. I'll
poke misc maintainers so it's not lost.
-Daniel

> 
> It will take a while until it cycles back into the development branches, so
> feel free to push some version to amd-staging-drm-next as well. Just ping
> Alex when you do this.
> 
> Thanks,
> Christian.
> 
> Am 07.09.21 um 06:08 schrieb xinhui pan:
> > The ret value might be -EBUSY, caller will think lru lock is still
> > locked but actually NOT. So return -ENOSPC instead. Otherwise we hit
> > list corruption.
> > 
> > ttm_bo_cleanup_refs might fail too if BO is not idle. If we return 0,
> > caller(ttm_tt_populate -> ttm_global_swapout ->ttm_device_swapout) will
> > be stuck as we actually did not free any BO memory. This usually happens
> > when the fence is not signaled for a long time.
> > 
> > Signed-off-by: xinhui pan <xinhui.pan@amd.com>
> > Reviewed-by: Christian König <christian.koenig@amd.com>
> > ---
> >   drivers/gpu/drm/ttm/ttm_bo.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> > index 8d7fd65ccced..23f906941ac9 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> > @@ -1152,9 +1152,9 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
> >   	}
> >   	if (bo->deleted) {
> > -		ttm_bo_cleanup_refs(bo, false, false, locked);
> > +		ret = ttm_bo_cleanup_refs(bo, false, false, locked);
> >   		ttm_bo_put(bo);
> > -		return 0;
> > +		return ret == -EBUSY ? -ENOSPC : ret;
> >   	}
> >   	ttm_bo_del_from_lru(bo);
> > @@ -1208,7 +1208,7 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
> >   	if (locked)
> >   		dma_resv_unlock(bo->base.resv);
> >   	ttm_bo_put(bo);
> > -	return ret;
> > +	return ret == -EBUSY ? -ENOSPC : ret;
> >   }
> >   void ttm_bo_tt_destroy(struct ttm_buffer_object *bo)
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch