linux-kernel - Re: PROBLEM: repeated remap_file_pages on tmpfs triggers bug on process exit

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Message-Id: <20140715105547.C4832E00A3@blue.fi.intel.com>
Date:	Tue, 15 Jul 2014 13:55:47 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Konstantin Khlebnikov <koct9i@...il.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Ingo Korb <ingo.korb@...dortmund.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Ning Qu <quning@...gle.com>, Dave Jones <davej@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: PROBLEM: repeated remap_file_pages on tmpfs triggers bug on
 process exit

Konstantin Khlebnikov wrote:
> It seems boundng logic in do_fault_around is wrong:
> 
> start_addr = max(address & fault_around_mask(), vma->vm_start);
> off = ((address - start_addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
> pte -= off;
> pgoff -= off;
> 
> Ok, off  <= 511, but it might be bigger than pte offset in pte table.

I don't see how it possible: fault_around_mask() cannot be more than 0x1ff000
(x86-64, fault_around_bytes == 2M). It means start_addr will be aligned to 2M
boundary in this case which is start of the page table pte belong to.

Do I miss something?

-- 
 Kirill A. Shutemov
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