[PATCH v2 0/2] drm/amdgpu: fix locking issues in PASID IDR management

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

Commit 8f1de51f49be ("drm/amdgpu: prevent immediate PASID reuse case")
converted the global PASID allocator from IDA to IDR with a spinlock
for cyclic allocation.  This introduced two locking bugs:
 
1) idr_alloc_cyclic() is called with GFP_KERNEL under spin_lock(),
   which can sleep.
 
2) amdgpu_pasid_free() can be called from hardirq context via the
   fence signal path (amdgpu_pasid_free_cb), but the lock is taken
   with plain spin_lock() in process context, creating a potential
   deadlock:
 
     CPU0
     ----
     spin_lock(&amdgpu_pasid_idr_lock)   // process context, IRQs on
     <Interrupt>
       spin_lock(&amdgpu_pasid_idr_lock) // deadlock
 
   The hardirq call chain is:
 
     sdma_v6_0_process_trap_irq
      -> amdgpu_fence_process
       -> dma_fence_signal
        -> drm_sched_job_done
         -> dma_fence_signal
          -> amdgpu_pasid_free_cb
           -> amdgpu_pasid_free
 
   This was observed on an RX 7900 XTX when exiting a Vulkan game
   running under Proton/Wine, which triggers the fence callback path
   during VM teardown.
 
Patch 1 fixes the sleeping-under-spinlock by using idr_preload() with
GFP_KERNEL before taking the lock, then GFP_NOWAIT for the actual
allocation.
 
Patch 2 converts all three spin_lock/spin_unlock call sites to
spin_lock_irqsave/spin_unlock_irqrestore.
 
Tested on ASUS ROG STRIX B650E-I / Ryzen 9 7950X / RX 7900 XTX with
CONFIG_PROVE_LOCKING=y.  The lockdep warning is no longer triggered
after applying both patches.

Mikhail Gavrilov (2):
  drm/amdgpu: fix sleeping allocation under spinlock in PASID IDR
  drm/amdgpu: use spin_lock_irqsave for PASID IDR lock

 drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

-- 
2.53.0