linux-kernel - Re: [PATCH] drm/lease: fix WARNING in idr

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Date:   Tue, 17 Mar 2020 17:57:29 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Qiujun Huang <hqjagain@...il.com>
Cc:     maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        airlied@...ux.ie, daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/lease: fix WARNING in idr_destroy

On Mon, Mar 16, 2020 at 11:36:08AM +0800, Qiujun Huang wrote:
> leases has been destroyed:
> drm_master_put
>     ->drm_master_destroy
>             ->idr_destroy
> 
> so the "out_lessee" needn't to call idr_destroy again.
> 
> Reported-and-tested-by: syzbot+05835159fe322770fe3d@...kaller.appspotmail.com
> Signed-off-by: Qiujun Huang <hqjagain@...il.com>
> ---
>  drivers/gpu/drm/drm_lease.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c
> index b481caf..54506c2 100644
> --- a/drivers/gpu/drm/drm_lease.c
> +++ b/drivers/gpu/drm/drm_lease.c
> @@ -577,11 +577,14 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev,
>  
>  out_lessee:
>  	drm_master_put(&lessee);
> +	goto err_exit;

I think this is correct, but also confusioning and inconsistent with the
existing style. Most error cases before drm_lease_create explicit destroy
the idr, except the one for drm_lease_create.

Instead of your patch I'd
- remove the idr_destry from the error unrolling here
- add it the to drm_lease_create error case
- add a comment above the call to drm_lease_crete that it takes ownership
  of the lease idr

Can you pls respin and retest to make sure that patch is still correct?

Thanks, Daniel

>  
>  out_leases:
> -	put_unused_fd(fd);
>  	idr_destroy(&leases);
>  
> +err_exit:
> +	put_unused_fd(fd);
> +
>  	DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl failed: %d\n", ret);
>  	return ret;
>  }
> -- 
> 1.8.3.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch