Re: [PATCH v3] drm/nouveau: prime: fix ttm_bo_delayed_delete oops

[Danilo Krummrich <dakr@kernel.org>]

On Wed, Mar 26, 2025 at 12:52:10PM +0000, Chris Bainbridge wrote:
> 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 #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 <chris.bainbridge@gmail.com>
> Suggested-by: Christian König <christian.koenig@amd.com>
> Fixes: 22b33e8ed0e3 ("22b33e8ed0e3nouveau: add PRIME support")
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3937
> Cc: <Stable@vger.kernel.org>

Applied to drm-misc-fixes, thanks!

[ Fixed up the Fixes: tag, where the commit hash is repeated in the commit
subject. ]