Re: [PATCH v2] drm/nouveau: prime: fix ttm_bo_delayed_delete oops

[Danilo Krummrich]

Hi Chris,

Thanks for the fix, few comments below.

On Wed, Mar 19, 2025 at 12:54:26PM +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@xxxxxxxxx>
> Co-Developed-by: Christian König <christian.koenig@xxxxxxx>

Then also Christian's SoB is required.

> Fixes: https://gitlab.freedesktop.org/drm/amd/-/issues/3937

This is a bug report from amdgpu, but I understand that the same issue applies
for nouveau.

If at all, this needs to be

	Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3937

Maybe you can add a brief comment that this report applies for nouveau as well.

Please also add a Fixes: tag that indicates the commit in nouveau that
introduced the problem and Cc stable.

> ---
>  drivers/gpu/drm/drm_prime.c           | 8 ++++++--
>  drivers/gpu/drm/nouveau/nouveau_bo.c  | 3 +++
>  drivers/gpu/drm/nouveau/nouveau_gem.c | 3 ---
>  3 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 32a8781cfd67..452d5c7cd292 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/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.
> + * &drm_gem_object_funcs.free hook or &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.
> + * &drm_gem_object_funcs.free hook or &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)

Please send a separate commit for the changes in drm_prime.c.

> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index db961eade225..2016c1e7242f 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/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.
> diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c
> index 9ae2cee1c7c5..67e3c99de73a 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> +++ b/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);
> -- 
> 2.47.2
>