linux-kernel - Re: [RFC PATCH 1/1] mm/percpu.c: fix potential memory leakage for pcpu_embed_first

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Message-ID: <20160929164422.GA3773@mtj.duckdns.org>
Date:   Thu, 29 Sep 2016 18:44:22 +0200
From:   Tejun Heo <tj@...nel.org>
To:     zijun_hu <zijun_hu@...o.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, zijun_hu@....com,
        cl@...ux.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] mm/percpu.c: fix potential memory leakage for
 pcpu_embed_first_chunk()

Hello,

On Fri, Sep 30, 2016 at 12:03:20AM +0800, zijun_hu wrote:
> From: zijun_hu <zijun_hu@....com>
> 
> it will cause memory leakage for pcpu_embed_first_chunk() to go to
> label @out_free if the chunk spans over 3/4 VMALLOC area. all memory
> are allocated and recorded into array @areas for each CPU group, but
> the memory allocated aren't be freed before returning after going to
> label @out_free
> 
> in order to fix this bug, we check chunk spanned area immediately
> after completing memory allocation for all CPU group, we go to label
> @out_free_areas other than @out_free to free all memory allocated if
> the checking is failed.
> 
> Signed-off-by: zijun_hu <zijun_hu@....com>
...
> @@ -2000,6 +2001,21 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
>  		areas[group] = ptr;
>  
>  		base = min(ptr, base);
> +		if (ptr > areas[j])
> +			j = group;
> +	}
> +	max_distance = areas[j] - base;
> +	max_distance += ai->unit_size * ai->groups[j].nr_units;
> +
> +	/* warn if maximum distance is further than 75% of vmalloc space */
> +	if (max_distance > VMALLOC_TOTAL * 3 / 4) {
> +		pr_warn("max_distance=0x%lx too large for vmalloc space 0x%lx\n",
> +				max_distance, VMALLOC_TOTAL);
> +#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
> +		/* and fail if we have fallback */
> +		rc = -EINVAL;
> +		goto out_free_areas;
> +#endif

Isn't it way simpler to make the error path jump to out_free_areas?
There's another similar case after pcpu_setup_first_chunk() failure
too.  Also, can you please explain how you tested the changes?

Thanks.

-- 
tejun