linux-kernel - Re: UBSAN: Undefined behaviour in mm/page

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Date:   Fri, 9 Nov 2018 18:41:53 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>, Kyungtae Kim <kt0755@...il.com>
Cc:     akpm@...ux-foundation.org, pavel.tatashin@...rosoft.com,
        vbabka@...e.cz, osalvador@...e.de, rppt@...ux.vnet.ibm.com,
        aaron.lu@...el.com, iamjoonsoo.kim@....com,
        alexander.h.duyck@...ux.intel.com, mgorman@...hsingularity.net,
        lifeasageek@...il.com, threeearcat@...il.com,
        syzkaller@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c

On 2018/11/09 17:43, Michal Hocko wrote:
> @@ -4364,6 +4353,17 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid,
>  	gfp_t alloc_mask; /* The gfp_t that was actually used for allocation */
>  	struct alloc_context ac = { };
>  
> +	/*
> +	 * In the slowpath, we sanity check order to avoid ever trying to

Please keep the comment up to dated.
I don't like that comments in OOM code is outdated.

> +	 * reclaim >= MAX_ORDER areas which will never succeed. Callers may
> +	 * be using allocators in order of preference for an area that is
> +	 * too large.
> +	 */
> +	if (order >= MAX_ORDER) {

Also, why not to add BUG_ON(gfp_mask & __GFP_NOFAIL); here?

> +		WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN));
> +		return NULL;
> +	}
> +
>  	gfp_mask &= gfp_allowed_mask;
>  	alloc_mask = gfp_mask;
>  	if (!prepare_alloc_pages(gfp_mask, order, preferred_nid, nodemask, &ac, &alloc_mask, &alloc_flags))
>