gem context refcounting is another exercise in least locking design it

seems, where most things get destroyed upon context closure (which can

race with anything really). Only the actual memory allocation and the

locks survive while holding a reference.

This tripped up Jason when reimplementing the single timeline feature

in

commit 00dae4d3d35d4f526929633b76e00b0ab4d3970d

Author: Jason Ekstrand <jason@jlekstrand.net>

Date:   Thu Jul 8 10:48:12 2021 -0500

    drm/i915: Implement SINGLE_TIMELINE with a syncobj (v4)

We could fix the bug by holding ctx->mutex, but it's cleaner to just

make the context object actually invariant over its _entire_ lifetime.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Fixes: 00dae4d3d35d ("drm/i915: Implement SINGLE_TIMELINE with a syncobj (v4)")

Cc: Jason Ekstrand <jason@jlekstrand.net>

Cc: Chris Wilson <chris@chris-wilson.co.uk>

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Cc: Matthew Brost <matthew.brost@intel.com>

Cc: Matthew Auld <matthew.auld@intel.com>

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

Cc: "Thomas Hellström" <thomas.hellstrom@intel.com>

Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

Cc: Dave Airlie <airlied@redhat.com>

---

 drivers/gpu/drm/i915/gem/i915_gem_context.c | 6 +++---

 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c

index 754b9b8d4981..93ba0197d70a 100644

--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c

+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -940,6 +940,9 @@ void i915_gem_context_release(struct kref *ref)

  trace_i915_context_free(ctx);

  GEM_BUG_ON(!i915_gem_context_is_closed(ctx));

 

+ if (ctx->syncobj)

+ drm_syncobj_put(ctx->syncobj);

+

  mutex_destroy(&ctx->engines_mutex);

  mutex_destroy(&ctx->lut_mutex);

 

@@ -1159,9 +1162,6 @@ static void context_close(struct i915_gem_context *ctx)

  if (vm)

  i915_vm_close(vm);

 

- if (ctx->syncobj)

- drm_syncobj_put(ctx->syncobj);

-

  ctx->file_priv = ERR_PTR(-EBADF);

 

  /*

-- 

2.32.0