Re: [PATCH] mm: fix incorrect behavior when process virtual address space limit is exceeded

From: Oleg Nesterov <oleg@redhat.com>
To: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Piotr Kwapulinski <kwapulinski.piotr@gmail.com>,
	akpm@linux-foundation.org, mszeredi@suse.cz,
	viro@zeniv.linux.org.uk, dave@stgolabs.net,
	kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com,
	aarcange@redhat.com, mhocko@suse.com, iamjoonsoo.kim@lge.com,
	jack@suse.cz, xiexiuqi@huawei.com, vbabka@suse.cz,
	Vineet.Gupta1@synopsys.com, riel@redhat.com,
	gang.chen.5i5j@gmail.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH] mm: fix incorrect behavior when process virtual address space limit is exceeded
Date: Tue, 17 Nov 2015 20:03:50 +0100	[thread overview]
Message-ID: <20151117190350.GA9790@redhat.com> (raw)
In-Reply-To: <564B6605.8080808@ezchip.com>

On 11/17, Chris Metcalf wrote:
>
> On 11/17/2015 11:19 AM, Oleg Nesterov wrote:
>> On 11/16, Piotr Kwapulinski wrote:
>>> @@ -1551,7 +1552,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>>>   		 * MAP_FIXED may remove pages of mappings that intersects with
>>>   		 * requested mapping. Account for the pages it would unmap.
>>>   		 */
>>> -		if (!(vm_flags & MAP_FIXED))
>>> +		if (!(flags & MAP_FIXED))
>>>   			return -ENOMEM;
>> And afaics arch/tile/mm/elf.c can use do_mmap(MAP_FIXED ...) rather than
>> mmap_region(), it can be changed by a separate patch. In this case we can
>> unexport mmap_region().
>
> The problem is that we are mapping a region of virtual address space that
> the chip provides for setting up interrupt handlers (at 0xfc000000) but that
> is above the TASK_SIZE cutoff,

Ah, I didn't bother to read the comment in arch_setup_additional_pages().
Thanks for your explanation.

Oleg.