linux-kernel - Re: [PATCH] drm/ttm: optimize errors checking and free

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Date:   Tue, 2 Jan 2018 10:29:45 +0100
From:   Christian König <christian.koenig@....com>
To:     "He, Roger" <Hongbo.He@....com>, Xiongwei Song <sxwjean@...il.com>,
        "airlied@...ux.ie" <airlied@...ux.ie>
Cc:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/ttm: optimize errors checking and free _manager when
 finishing

Am 02.01.2018 um 04:05 schrieb He, Roger:
>
> -----Original Message-----
> From: Xiongwei Song [mailto:sxwjean@...il.com]
> Sent: Sunday, December 31, 2017 7:40 PM
> To: Koenig, Christian <Christian.Koenig@....com>; He, Roger <Hongbo.He@....com>; airlied@...ux.ie
> Cc: dri-devel@...ts.freedesktop.org; linux-kernel@...r.kernel.org
> Subject: [PATCH] drm/ttm: optimize errors checking and free _manager when finishing
>
> In the function ttm_page_alloc_init, kzalloc call is made for variable _manager, we need to check its return value, it may return NULL.
>
> In the function ttm_page_alloc_fini, we need to call kfree for variable _manager, instead of make _manager NULL directly.
>
> Signed-off-by: Xiongwei Song <sxwjean@...il.com>
> ---
>   drivers/gpu/drm/ttm/ttm_page_alloc.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc.c b/drivers/gpu/drm/ttm/ttm_page_alloc.c
> index b5ba6441489f..e20a0b8e352b 100644
> --- a/drivers/gpu/drm/ttm/ttm_page_alloc.c
> +++ b/drivers/gpu/drm/ttm/ttm_page_alloc.c
> @@ -1007,6 +1007,10 @@ int ttm_page_alloc_init(struct ttm_mem_global *glob, unsigned max_pages)
>   	pr_info("Initializing pool allocator\n");
>   
>   	_manager = kzalloc(sizeof(*_manager), GFP_KERNEL);
> +	if (!_manager) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> Seems we only need above here for this patch I think.
> The rest is no need, because ttm_pool_kobj_release will kfree _manager.

Yes, agree. Freeing it again in ttm_page_alloc_fini will actually double 
free the memory and probably cause some problems.

Please refine the patch with only the additional error handling.

Regards,
Christian.

>
>
> Thanks
> Roger(Hongbo.He)
>
>   	ttm_page_pool_init_locked(&_manager->wc_pool, GFP_HIGHUSER, "wc", 0);
>   
> @@ -1034,13 +1038,17 @@ int ttm_page_alloc_init(struct ttm_mem_global *glob, unsigned max_pages)
>   				   &glob->kobj, "pool");
>   	if (unlikely(ret != 0)) {
>   		kobject_put(&_manager->kobj);
> -		_manager = NULL;
> -		return ret;
> +		goto out_free_mgr;
>   	}
>   
>   	ttm_pool_mm_shrink_init(_manager);
>   
>   	return 0;
> +out_free_mgr:
> +	kfree(_manager);
> +	_manager = NULL;
> +out:
> +	return ret;
>   }
>   
>   void ttm_page_alloc_fini(void)
> @@ -1055,6 +1063,7 @@ void ttm_page_alloc_fini(void)
>   		ttm_page_pool_free(&_manager->pools[i], FREE_ALL_PAGES, true);
>   
>   	kobject_put(&_manager->kobj);
> +	kfree(_manager);
>   	_manager = NULL;
>   }
>   
> --
> 2.15.1
>