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Date:   Thu, 21 Feb 2019 09:23:09 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Yue Hu <zbestahu@gmail.com>
Cc:     akpm@linux-foundation.org, rientjes@google.com, joe@perches.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        huyue2@yulong.com, Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] mm/cma_debug: Check for null tmp in cma_debugfs_add_one()
Message-ID: <20190221082309.GG4525@dhcp22.suse.cz>
References: <20190221040130.8940-1-zbestahu@gmail.com>
 <20190221040130.8940-2-zbestahu@gmail.com>
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On Thu 21-02-19 12:01:30, Yue Hu wrote:
> From: Yue Hu <huyue2@yulong.com>
> 
> If debugfs_create_dir() failed, the following debugfs_create_file()
> will be meanless since it depends on non-NULL tmp dentry and it will
> only waste CPU resource.

The file will be created in the debugfs root. But, more importantly.
Greg (CCed now) is working on removing the failure paths because he
believes they do not really matter for debugfs and they make code more
ugly. More importantly a check for NULL is not correct because you
get ERR_PTR after recent changes IIRC.

> 
> Signed-off-by: Yue Hu <huyue2@yulong.com>
> ---
>  mm/cma_debug.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/cma_debug.c b/mm/cma_debug.c
> index 2c2c869..3e9d984 100644
> --- a/mm/cma_debug.c
> +++ b/mm/cma_debug.c
> @@ -169,6 +169,8 @@ static void cma_debugfs_add_one(struct cma *cma, struct dentry *root_dentry)
>  	scnprintf(name, sizeof(name), "cma-%s", cma->name);
>  
>  	tmp = debugfs_create_dir(name, root_dentry);
> +	if (!tmp)
> +		return;
>  
>  	debugfs_create_file("alloc", 0200, tmp, cma, &cma_alloc_fops);
>  	debugfs_create_file("free", 0200, tmp, cma, &cma_free_fops);
> -- 
> 1.9.1
> 

-- 
Michal Hocko
SUSE Labs