linux-kernel - Re: [PATCH] mm: fix invalid node in alloc_migrate

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Message-ID: <56FA732E.9020906@suse.cz>
Date:	Tue, 29 Mar 2016 14:21:02 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Xishi Qiu <qiuxishi@...wei.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <js1304@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Laura Abbott <lauraa@...eaurora.org>, zhuhui@...omi.com,
	wangxq10@....edu.cn, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH] mm: fix invalid node in alloc_migrate_target()

On 03/29/2016 12:37 PM, Xishi Qiu wrote:
> On 2016/3/29 17:52, Vlastimil Babka wrote:
>> The code in this functions seems to come from 099730d67417d ("mm, hugetlb: use memory policy when available") by Dave Hansen (adding to CC), which was indeed merged in 4.4-rc1.
>>
>> However, alloc_pages_node() is only called in the block guarded by:
>>
>> if (!IS_ENABLED(CONFIG_NUMA) || !vma) {
>>
>> The rather weird "!IS_ENABLED(CONFIG_NUMA)" part comes from immediate followup commit e0ec90ee7e6f ("mm, hugetlbfs: optimize when NUMA=n")
>>
>> So I doubt the code path here can actually happen. But it's fragile and confusing nevertheless.
>>
>
> Hi Vlastimil
>
> __alloc_buddy_huge_page(h, NULL, addr, nid); // so the vma is NULL

Hm that's true, I got lost in the logic, thanks.
But the problem with dequeue_huge_page_node() is also IMHO true, and 
older, so we should fix 3.12+.