drm/xe: Link LRC BO and its execution queue with safe lifetime rules

Browse source

Introduce an execution queue back-pointer (`q`) within `struct xe_bo`, primarily
for Logical Ring Context (LRC) Buffer Objects. This back-pointer allows the
driver to identify and execute targeted corrective actions on a specific queue
if its associated LRC BO encounters errors like memory corruption or eviction.

Because this back-pointer takes no reference on its target execution queue, strict
lifetime and serialization rules are implemented to prevent concurrent readers
from encountering use-after-free or dangling pointer bugs:

- Encapsulate tracking logic inside xe_exec_queue_set_lrc_bo_backpointer() and
  xe_exec_queue_clear_lrc_bo_backpointer().

- Explicitly wrap all back-pointer writes and clears under the BO's dma_resv lock
  via xe_bo_lock(). Readers must hold this same lock across both the pointer read
  and its subsequent xe_exec_queue_get_unless_zero() call to guarantee serialization
  against teardown.

- Defer publishing the back-pointer until the very end of xe_exec_queue_create().
  This ensures that early initialization failure paths (which bypass the kref
  mechanism and immediately free the queue structure) never leak a transient pointer
  to concurrent readers.

- Clear the back-pointer at the absolute top of __xe_exec_queue_fini(). This strips
  the pointer before q->ops->fini() destroys the hardware backend, ensuring that
  any reader holding the BO lock either observes a fully functional queue or NULL.

For multi-queue engines, secondary LRC BOs safely point to the primary queue, which
is guaranteed to outlive the teardown pass due to active references held by its
secondaries.

V4 (MattB):
  - Add LRC BO's execution queue safe lifetime rules
V3 (Sashiko):
  - Use 8-byte placeholder structure compatibility for non-LRC BO cases.
  - Wrap assignments and clears securely under dma_resv locks.
V2 (Matt B):
  - Add native support handling multi-queue configuration tracking.

Assisted-by: Copilot:claude-opus-4.6
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260903161553.528932-19-tejas.upadhyay@intel.com

...

This commit is contained in:

Tejas Upadhyay 2026-09-03 21:45:55 +05:30 • committed by Matthew Brost

parent c1b1906f86

commit 4356370caf

2 changed files with 72 additions and 0 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

8

drivers/gpu/drm/xe/xe_bo_types.h

View file

64

drivers/gpu/drm/xe/xe_exec_queue.c

View file