Re: [Nouveau] [PATCH] drm/nouveau/core/object: fix double free on error in nvkm_ioctl_new()

[Dan Carpenter <dan.carpenter@oracle.com>]

On Mon, Jun 14, 2021 at 01:43:27PM +0300, Dan Carpenter wrote:
> If nvkm_object_init() fails then we should not call nvkm_object_fini()
> because it results in calling object->func->fini(object, suspend) twice.
> Once inside the nvkm_object_init() function and once inside the
> nvkm_object_fini() function.
> 
> Fixes: fbd58ebda9c8 ("drm/nouveau/object: merge with handle")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> This is something that I spotted while looking for reference counting
> bugs.  I have tried running it, but it does not fix my crashes.  My
> system is basically unusable.  It's something to do with the new version
> of Firefox which triggers the refcount_t underflow, but switching to
> Epiphany doesn't solve the issue either.
> 
>  drivers/gpu/drm/nouveau/nvkm/core/ioctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c b/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c
> index d777df5a64e6..87c761fb475a 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c
> @@ -134,8 +134,8 @@ nvkm_ioctl_new(struct nvkm_client *client,
>  				return 0;
>  			}
>  			ret = -EEXIST;
> +			nvkm_object_fini(object, false);
>  		}
> -		nvkm_object_fini(object, false);

Actually calling nvkm_object_fini() is probably fine.  It just screws
around with the registers and it's probably fine if we do that twice.

Calling .dtor() when .ctor() fails is actually required because .ctor
doesn't clean up after itself.

So this patch is not required.  The other patch is required.
https://lore.kernel.org/nouveau/YMinJwpIei9n1Pn1@mwanda/T/

In the end, I had to give up on fixing the hang and downgrade to
debian's long term support version of firefox.

regards,
dan carpenter

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