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.
 
The fix teaches amdgpu_vm_lock_by_pasid() to lock the root PD in a
drm_exec context, so the devcoredump path can lock the root PD and all
the IB BOs together in one ww ticket. 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 with drm_exec_lock_obj(). The drm_exec context
       holds the root BO reference, so the root output parameter is
       dropped. 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 IB dump is produced
correctly.
 
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/
v3: https://lore.kernel.org/amd-gfx/20260520151741.50575-1-mikhail.v.gavrilov@gmail.com/
v4: https://lore.kernel.org/amd-gfx/20260521104335.28978-1-mikhail.v.gavrilov@gmail.com/
 
Changes since v4:
- Pass nr=1 to drm_exec_init() in amdgpu_vm_handle_fault(), since
  exactly one object (the root PD) is locked there (Christian).
- Picked up Christian's Reviewed-by on patch 1.
 
Changes since v3:
- Lock the root PD with drm_exec_lock_obj() instead of
  amdgpu_vm_lock_pd(): the latter dereferences the VM pointer, which is
  not yet re-validated at that point (Christian).
- Drop the root output parameter of amdgpu_vm_lock_by_pasid() entirely;
  the drm_exec context already holds a reference on the locked root BO,
  so the extra reference and the parameter are unnecessary (Christian).
- Unlock the root BO with drm_exec_unlock_obj() on the VM-recheck-failed
  path (Christian).
- amdgpu_vm_handle_fault() and amdgpu_devcoredump_format() updated for
  the simplified signature; both lose their root variable.
- Drops the v3 kernel-doc "*root" reference, which also resolves the
  docutils "Inline emphasis start-string without end-string" warning
  the kernel test robot reported against v3.
 
Changes since v2:
- Reworked along the lines Christian suggested: amdgpu_vm_lock_by_pasid()
  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). The
  amdgpu_devcoredump_ib_ref struct and the three collect/lock/release
  helpers from v2 are gone.
 
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  | 105 ++++++++++++------
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c        |  91 +++++++++------
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h        |   2 +-
 3 files changed, 129 insertions(+), 69 deletions(-)

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2.54.0