[PATCH v2 1/2] drm/amdgpu: fix sleeping allocation under spinlock in PASID IDR

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

Commit 14b81abe7bdc ("drm/amdgpu: prevent immediate PASID reuse case")
switched from ida to idr_alloc_cyclic() protected by a spinlock, but
passes GFP_KERNEL to the allocator.  idr_alloc_cyclic() may need to
allocate radix-tree nodes, which with GFP_KERNEL can sleep — illegal
under a spinlock that disables preemption.  With CONFIG_PREEMPT or
lockdep enabled this triggers:

  BUG: sleeping function called from invalid context at
       ./include/linux/sched/mm.h:323
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 570
  ...
  #1: ffffffffc2cd24f8 (amdgpu_pasid_idr_lock){+.+.}-{3:3},
      at: amdgpu_pasid_alloc+0x24/0x210 [amdgpu]
  ...
  kmem_cache_alloc_noprof+0x41d/0x780
  radix_tree_node_alloc.constprop.0+0x56/0x3a0
  idr_get_free+0x330/0x830
  idr_alloc_u32+0x14a/0x2e0
  idr_alloc_cyclic+0xd3/0x1d0
  amdgpu_pasid_alloc+0x51/0x210 [amdgpu]

A mutex is not an option because amdgpu_pasid_free() is reachable from
dma-fence callbacks (amdgpu_pasid_free_cb) which may run in IRQ context.

Use idr_preload(GFP_KERNEL) before taking the spinlock to pre-allocate
radix-tree nodes, then pass GFP_NOWAIT inside the critical section so
the allocator draws from the preloaded pool and never sleeps.  This is
the standard kernel pattern for IDR allocation under a spinlock.

Fixes: 14b81abe7bdc ("drm/amdgpu: prevent immediate PASID reuse case")
Cc: stable@vger.kernel.org
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c
index d88523568b62..515775eab2ef 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c
@@ -67,10 +67,12 @@ int amdgpu_pasid_alloc(unsigned int bits)
 	if (bits == 0)
 		return -EINVAL;
 
+	idr_preload(GFP_KERNEL);
 	spin_lock(&amdgpu_pasid_idr_lock);
 	pasid = idr_alloc_cyclic(&amdgpu_pasid_idr, NULL, 1,
-				 1U << bits, GFP_KERNEL);
+				 1U << bits, GFP_NOWAIT);
 	spin_unlock(&amdgpu_pasid_idr_lock);
+	idr_preload_end();
 
 	if (pasid >= 0)
 		trace_amdgpu_pasid_allocated(pasid);
-- 
2.53.0