[PATCH 0/9] remove rcu support from i915_address_space

From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: DRI Development <dri-devel@lists.freedesktop.org>
Cc: Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Daniel Vetter <daniel.vetter@ffwll.ch>
Subject: [PATCH 0/9] remove rcu support from i915_address_space
Date: Mon,  2 Aug 2021 17:47:57 +0200	[thread overview]
Message-ID: <20210802154806.3710472-1-daniel.vetter@ffwll.ch> (raw)

Hi all,

Jason wanted to do that as part of the scheduler series, but I object
since rcu is very, very hard to review when adding, and much, much harder
even to review when removing.

This is because simply looking for __rcu pointer annotations and rcu
functions isn't enough, rcu is also relied upon in many datastructures
which have internally and rcu_read_lock protection (or at least the
required amount of barriers), like xarray.

The other problem is that it inherits when chasing pointers, e.g.
i915_gem_engines has an rcu pointer to intel_context, which has a non-rcu
pointer to i915_address_space. But since we could look-up the entire chain
under rcu i.e. engines->context[i]->vm this means more code to audit.

The audit explodes pretty quickly.

Anyway I'm reasonable confident I got them all in the current code, and
slightly less confident that I managed to stitch together the full
history.

References to relevant commits throughout the series.

Cheers, Daniel

Daniel Vetter (9):
  drm/i915: Drop code to handle set-vm races from execbuf
  drm/i915: Rename i915_gem_context_get_vm_rcu to
    i915_gem_context_get_eb_vm
  drm/i915: Use i915_gem_context_get_eb_vm in ctx_getparam
  drm/i915: Add i915_gem_context_is_full_ppgtt
  drm/i915: Use i915_gem_context_get_eb_vm in intel_context_set_gem
  drm/i915: Drop __rcu from gem_context->vm
  drm/i915: use xa_lock/unlock for fpriv->vm_xa lookups
  drm/i915: Stop rcu support for i915_address_space
  drm/i915: Split out intel_context_create_user

 drivers/gpu/drm/i915/gem/i915_gem_context.c   | 82 ++++---------------
 drivers/gpu/drm/i915/gem/i915_gem_context.h   | 13 ++-
 .../gpu/drm/i915/gem/i915_gem_context_types.h |  2 +-
 .../gpu/drm/i915/gem/i915_gem_execbuffer.c    | 12 ++-
 .../gpu/drm/i915/gem/selftests/huge_pages.c   |  8 +-
 .../drm/i915/gem/selftests/i915_gem_context.c | 32 +++-----
 .../gpu/drm/i915/gem/selftests/mock_context.c |  2 +-
 drivers/gpu/drm/i915/gt/intel_context.c       | 22 ++++-
 drivers/gpu/drm/i915/gt/intel_context.h       |  2 +
 drivers/gpu/drm/i915/gt/intel_ggtt.c          |  1 -
 drivers/gpu/drm/i915/gt/intel_gtt.c           |  6 +-
 drivers/gpu/drm/i915/gt/intel_gtt.h           |  2 +-
 drivers/gpu/drm/i915/gt/selftest_execlists.c  |  2 +-
 drivers/gpu/drm/i915/gt/selftest_hangcheck.c  |  2 +-
 drivers/gpu/drm/i915/i915_drv.h               |  4 +-
 drivers/gpu/drm/i915/i915_trace.h             |  2 +-
 drivers/gpu/drm/i915/selftests/i915_gem_gtt.c |  4 +-
 drivers/gpu/drm/i915/selftests/i915_vma.c     |  4 +-
 18 files changed, 79 insertions(+), 123 deletions(-)

-- 
2.32.0