linux-kernel - Re: remap_file

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Message-ID: <CAAih0NhTXOb+Hj+u+0QLrADxyOYc-EwHDCx5+1Fq7wiJsaY=_Q@mail.gmail.com>
Date:	Mon, 26 May 2014 08:38:19 -0500
From:	Jeff Smith <jsmith.lkml@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Christoph Hellwig <hch@...radead.org>,
	Kenny Simpson <theonetruekenny@...il.com>,
	Michal Hocko <mhocko@...e.cz>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: remap_file_pages() use

OK, I misinterpreted "the overlapped part of the mapping(s) will be
discarded" as discarding the -new- mappings. My objections about
needing a replacement for remap_file_pages() are gone, but my concerns
about existing code still remain.
--Jeff

On Mon, May 26, 2014 at 8:35 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> Il 26/05/2014 15:24, Jeff Smith ha scritto:
>
>> Your addr2 mmap() call is a bit incorrect semantically and
>> syntactically (you skipped the length arg). The addr2 request will
>> fail because mmap() does not implicitly munmap() occupied virtual
>> address space.
>
>
> With MAP_FIXED it does.  It is in the man page.
>
> Paolo
>
>
>> Even if you did that, the following still has a race
>> condition between the addr2 request and another thread grabbing the
>> same virtual space, which nothing short of a lock on all threads'
>> mmap()-ing logic can protect:
>
>
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