In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu: fix recursive ww_mutex acquire in amdgpu_devcoredump_format
When dumping IB contents from a hung job, amdgpu_devcoredump_format()
acquired the VM root PD's reservation via amdgpu_vm_lock_by_pasid() and
then, for each IB, called amdgpu_bo_reserve() on the BO backing the IB.
Both reservations are reservation_ww_class_mutex objects and neither
used a ww_acquire_ctx, which trips lockdep:
WARNING: possible recursive locking detected
<hr />
kworker/u128:0 is trying to acquire lock:
ffff88838b16e1f0 (reservation_ww_class_mutex){+.+.}-{4:4},
at: amdgpu_devcoredump_format+0x1594/0x23f0 [amdgpu]
but task is already holding lock:
ffff8882f82681f0 (reservation_ww_class_mutex){+.+.}-{4:4},
at: amdgpu_devcoredump_format+0x1594/0x23f0 [amdgpu]
Possible unsafe locking scenario:
CPU0
----
lock(reservation_ww_class_mutex);
lock(reservation_ww_class_mutex);
*** DEADLOCK ***
May be due to missing lock nesting notation
Workqueue: events_unbound amdgpu_devcoredump_deferred_work [amdgpu]
Call Trace:
__ww_mutex_lock.constprop.0
ww_mutex_lock
amdgpu_bo_reserve
amdgpu_devcoredump_format+0x1594 [amdgpu]
amdgpu_devcoredump_deferred_work+0xea [amdgpu]
The two reservations are on different BOs in the captured trace, so the
splat is a lockdep-correctness warning, not an observed deadlock. It
becomes a real self-deadlock whenever the IB BO shares its dma_resv with
the root PD (the always-valid case, see amdgpu_vm_is_bo_always_valid()):
amdgpu_bo_reserve(abo) re-acquires the same ww_mutex without a ticket
and blocks forever. With amdgpu.gpu_recovery=0 the timeout handler
refires every ~2 s and each invocation produces this splat, drowning the
kernel ring buffer.
Now that amdgpu_vm_lock_by_pasid() takes a drm_exec context, move the IB
dumping into a separate helper that locks the root PD and every IB BO
together in a single drm_exec ticket. DRM_EXEC_IGNORE_DUPLICATES handles
IB BOs that share a dma_resv (e.g. always-valid BOs, or two IBs backed
by the same BO). Every lock is now a top-level acquire under one
ww_acquire_ctx, so the recursive ww_mutex condition is gone, and the
per-IB amdgpu_bo_reserve()/amdgpu_bo_unref() dance -- including a BO
refcount leak on the amdgpu_bo_reserve() failure path -- is removed.
(cherry picked from commit d6bf4242731219ee08ce54c365631e395486651e)