[PATCH v3 0/2] drm/amdgpu: fix recursive ww_mutex in devcoredump IB dump

[Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>]

This series fixes a lockdep "possible recursive locking" splat in
amdgpu_devcoredump_format() that fires on every GPU timeout once a job
with a PASID context is involved. With amdgpu.gpu_recovery=0 the timeout
handler refires every ~2 s, so the splat repeats until it drowns the
kernel ring buffer. It is also a real self-deadlock for IB BOs that
share their dma_resv with the root PD (the always-valid case).
 
The root cause: amdgpu_devcoredump_format() holds the VM root PD's
reservation and then reserves each IB BO on top of it, nesting two
reservation_ww_class_mutex acquires without a ww_acquire_ctx.
 
v1 fixed this with a snapshot helper that collected BO references under
the root reservation and reserved them one by one afterwards. Christian
pointed out that drm_exec already solves exactly this — lock everything
in one ww ticket — and suggested teaching amdgpu_vm_lock_by_pasid()
to take a drm_exec context. This v3 follows that approach.
 
Because amdgpu_vm_lock_by_pasid() has a second caller in the page-fault
path, the series is split so each patch builds and works on its own:
 
  1/2  Convert amdgpu_vm_lock_by_pasid() to take a drm_exec context and
       lock the root PD via amdgpu_vm_lock_pd(). Updates the existing
       caller, amdgpu_vm_handle_fault(). Pure refactor, no functional
       change to the page-fault path.
 
  2/2  Use the new signature in amdgpu_devcoredump_format(): lock the
       root PD and every IB BO together in one drm_exec ticket. The
       per-IB amdgpu_bo_reserve() nesting is gone, along with a BO
       refcount leak on the old reserve-failure path. This is the
       actual bug fix and carries the Fixes: tag.
 
Tested on Linux 7.1-rc4 + this series, Radeon RX 7900 XTX (gfx1100),
KASAN + PROVE_LOCKING enabled, using a small libdrm_amdgpu reproducer
that submits a GFX IB chained at GPU VA 0 and waits for the hang. Before
the series the splat fires on every TDR; after it the dmesg is clean
across repeated timeouts and the devcoredump output is unchanged.
 
v1: https://lore.kernel.org/amd-gfx/20260429143743.50743-1-mikhail.v.gavrilov@gmail.com/
v2: https://lore.kernel.org/amd-gfx/20260519161541.19994-1-mikhail.v.gavrilov@gmail.com/
 
Changes since v2:
- Reworked along the lines Christian suggested: instead of a private
  snapshot helper and a separate drm_exec pass, amdgpu_vm_lock_by_pasid()
  now takes a drm_exec context directly (patch 1), and the devcoredump
  code locks the root PD and all IB BOs in a single ticket (patch 2).
- Dropped the amdgpu_devcoredump_ib_ref struct and the three
  collect/lock/release helpers from v2 entirely.
 
Changes since v1:
- Switched from per-IB amdgpu_bo_reserve() to drm_exec.
- Dropped the Cc: stable tag: the regression only landed in 7.1-rc1, so
  the fix reaches 7.1 via drm-fixes without a stable backport.

Mikhail Gavrilov (2):
  drm/amdgpu: convert amdgpu_vm_lock_by_pasid() to drm_exec
  drm/amdgpu: fix recursive ww_mutex acquire in
    amdgpu_devcoredump_format

 .../gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c  | 103 ++++++++++++------
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c        |  72 ++++++++----
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h        |   3 +-
 3 files changed, 122 insertions(+), 56 deletions(-)

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2.54.0