[PATCH 0/2] Add BO reservation to GEM VRAM pin/unpin/push_to_system

[Thomas Zimmermann]

A kernel test bot reported a problem with the locktorture testcase that
was triggered by the GEM VRAM helpers.

  ...
  [   10.004734] RIP: 0010:ttm_bo_validate+0x41/0x141 [ttm]
  ...
  [   10.015669]  ? kvm_sched_clock_read+0x5/0xd
  [   10.016157]  ? get_lock_stats+0x11/0x3f
  [   10.016607]  drm_gem_vram_pin+0x77/0xa2 [drm_vram_helper]
  [   10.017229]  drm_gem_vram_driver_gem_prime_vmap+0xe/0x39 [drm_vram_helper]
  [   10.018015]  drm_gem_vmap+0x36/0x43 [drm]
  [   10.018491]  drm_client_framebuffer_create+0xc6/0x1ca [drm]
  [   10.019143]  drm_fb_helper_generic_probe+0x4c/0x157 [drm_kms_helper]
  [   10.019864]  __drm_fb_helper_initial_config_and_unlock+0x307/0x442 [drm_kms_helper]
  [   10.020739]  drm_fbdev_client_hotplug+0xc8/0x115 [drm_kms_helper]
  [   10.021442]  drm_fbdev_generic_setup+0xc4/0xf1 [drm_kms_helper]
  [   10.022120]  bochs_pci_probe+0x123/0x143 [bochs_drm]
  [   10.022688]  local_pci_probe+0x34/0x75
  [   10.023127]  pci_device_probe+0xf8/0x150A
  ...

It turns out that the bochs and vbox drivers automatically reserved and
unreserved the BO from within their pin and unpin functions. The other
drivers; ast, hibmc and mgag200; performed reservation explicitly. With the
GEM VRAM conversion, automatic BO reservation within pin and unpin functions
accidentally got lost. So for bochs and vbox, ttm_bo_validate() worked on
unlocked BOs.

This patch set fixes the problem by adding automatic reservation to the
implementation of drm_gem_vram_{pin,unpin,push_to_system}() to fix bochs
and vbox. It removes explicit BO reservation around the pin, unpin and
push-to-system calls in the ast, hibmc and mgag200 drivers.

The only exception is the cursor handling of mgag200. In this case, the
mgag200 driver now calls drm_gem_vram_{pin,unpin}_reserved(), which works
with reserved BOs. The respective code should be refactored in a future
patch to work with the regular pin and unpin functions.

Thomas Zimmermann (2):
  drm: Add drm_gem_vram_{pin/unpin}_reserved() and convert mgag200
  drm: Reserve/unreserve GEM VRAM BOs from within pin/unpin functions

 drivers/gpu/drm/ast/ast_mode.c                |  24 +---
 drivers/gpu/drm/drm_gem_vram_helper.c         | 115 +++++++++++++++++-
 .../gpu/drm/hisilicon/hibmc/hibmc_drm_de.c    |   6 -
 .../gpu/drm/hisilicon/hibmc/hibmc_drm_fbdev.c |  17 +--
 drivers/gpu/drm/mgag200/mgag200_cursor.c      |  18 +--
 drivers/gpu/drm/mgag200/mgag200_mode.c        |  19 +--
 include/drm/drm_gem_vram_helper.h             |   3 +
 7 files changed, 126 insertions(+), 76 deletions(-)

--
2.21.0