drm/nouveau: prime: fix ttm_bo_delayed_delete oops

Fix an oops in ttm_bo_delayed_delete which results from dererencing a
dangling pointer:

Oops: general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b7b: 0000 [#1] PREEMPT SMP
CPU: 4 UID: 0 PID: 1082 Comm: kworker/u65:2 Not tainted 6.14.0-rc4-00267-g505460b44513-dirty torvalds#216
Hardware name: LENOVO 82N6/LNVNB161216, BIOS GKCN65WW 01/16/2024
Workqueue: ttm ttm_bo_delayed_delete [ttm]
RIP: 0010:dma_resv_iter_first_unlocked+0x55/0x290
Code: 31 f6 48 c7 c7 00 2b fa aa e8 97 bd 52 ff e8 a2 c1 53 00 5a 85 c0 74 48 e9 88 01 00 00 4c 89 63 20 4d 85 e4 0f 84 30 01 00 00 <41> 8b 44 24 10 c6 43 2c 01 48 89 df 89 43 28 e8 97 fd ff ff 4c 8b
RSP: 0018:ffffbf9383473d60 EFLAGS: 00010202
RAX: 0000000000000001 RBX: ffffbf9383473d88 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffbf9383473d78 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 6b6b6b6b6b6b6b6b
R13: ffffa003bbf78580 R14: ffffa003a6728040 R15: 00000000000383cc
FS:  0000000000000000(0000) GS:ffffa00991c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000758348024dd0 CR3: 000000012c259000 CR4: 0000000000f50ef0
PKRU: 55555554
Call Trace:
 <TASK>
 ? __die_body.cold+0x19/0x26
 ? die_addr+0x3d/0x70
 ? exc_general_protection+0x159/0x460
 ? asm_exc_general_protection+0x27/0x30
 ? dma_resv_iter_first_unlocked+0x55/0x290
 dma_resv_wait_timeout+0x56/0x100
 ttm_bo_delayed_delete+0x69/0xb0 [ttm]
 process_one_work+0x217/0x5c0
 worker_thread+0x1c8/0x3d0
 ? apply_wqattrs_cleanup.part.0+0xc0/0xc0
 kthread+0x10b/0x240
 ? kthreads_online_cpu+0x140/0x140
 ret_from_fork+0x40/0x70
 ? kthreads_online_cpu+0x140/0x140
 ret_from_fork_asm+0x11/0x20
 </TASK>

The cause of this is:

- drm_prime_gem_destroy calls dma_buf_put(dma_buf) which releases the
  reference to the shared dma_buf. The reference count is 0, so the
  dma_buf is destroyed, which in turn decrements the corresponding
  amdgpu_bo reference count to 0, and the amdgpu_bo is destroyed -
  calling drm_gem_object_release then dma_resv_fini (which destroys the
  reservation object), then finally freeing the amdgpu_bo.

- nouveau_bo obj->bo.base.resv is now a dangling pointer to the memory
  formerly allocated to the amdgpu_bo.

- nouveau_gem_object_del calls ttm_bo_put(&nvbo->bo) which calls
  ttm_bo_release, which schedules ttm_bo_delayed_delete.

- ttm_bo_delayed_delete runs and dereferences the dangling resv pointer,
  resulting in a general protection fault.

Fix this by moving the drm_prime_gem_destroy call from
nouveau_gem_object_del to nouveau_bo_del_ttm. This ensures that it will
be run after ttm_bo_delayed_delete.

Signed-off-by: Chris Bainbridge <[email protected]>
Co-Developed-by: Christian König <[email protected]>
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/3937

Author: chrisbainbridge

drivers/gpu/drm/drm_prime.c

@@ -929,7 +929,9 @@ EXPORT_SYMBOL(drm_gem_prime_export);
  * &drm_driver.gem_prime_import_sg_table internally.
  *
  * Drivers must arrange to call drm_prime_gem_destroy() from their
- * &drm_gem_object_funcs.free hook when using this function.
+ * &ttm_buffer_object.destroy hook when using this function,
+ * to avoid the dma_buf being freed while the ttm_buffer_object can still
+ * dereference it.
  */
 struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
 					    struct dma_buf *dma_buf,
@@ -999,7 +1001,9 @@ EXPORT_SYMBOL(drm_gem_prime_import_dev);
  * implementation in drm_gem_prime_fd_to_handle().
  *
  * Drivers must arrange to call drm_prime_gem_destroy() from their
- * &drm_gem_object_funcs.free hook when using this function.
+ * &ttm_buffer_object.destroy hook when using this function,
+ * to avoid the dma_buf being freed while the ttm_buffer_object can still
+ * dereference it.
  */
 struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
 					    struct dma_buf *dma_buf)

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -144,6 +144,9 @@ nouveau_bo_del_ttm(struct ttm_buffer_object *bo)
 	nouveau_bo_del_io_reserve_lru(bo);
 	nv10_bo_put_tile_region(dev, nvbo->tile, NULL);
 
+	if (bo->base.import_attach)
+		drm_prime_gem_destroy(&bo->base, bo->sg);
+
 	/*
 	 * If nouveau_bo_new() allocated this buffer, the GEM object was never
 	 * initialized, so don't attempt to release it.

drivers/gpu/drm/nouveau/nouveau_gem.c

@@ -87,9 +87,6 @@ nouveau_gem_object_del(struct drm_gem_object *gem)
 		return;
 	}
 
-	if (gem->import_attach)
-		drm_prime_gem_destroy(gem, nvbo->bo.sg);
-
 	ttm_bo_put(&nvbo->bo);
 
 	pm_runtime_mark_last_busy(dev);