[PATCH 0/2] drm: fix soft lockup when saturating vram

[Yunxiang Li]

When running multiple graphical application and vram is saturated, the
excessive swapping triggers the BUG_ON() in dma_resv_add_fences. The
root cause is that calling dma_resv_reserve_fences twice would shadow
the second call and this happens in amdgpu_cs_ioctl/amdgpu_gem_va_ioctl
path shadowing reserve calls made in ttm.

The first patch fixes a missing reserve surfaced by the stricter reserve
check below.

The second patch reworks dma_resv_reserve_fences to allow it to be called
multiple times. It also makes the error check more percise and less
costly, hopefully this would catch missing reserve more reliably.