linux-kernel - Re: [PATCH 06/17] arm: mmu

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Message-ID: <20110228145750.GA4911@flint.arm.linux.org.uk>
Date:	Mon, 28 Feb 2011 14:57:50 +0000
From:	Russell King <rmk@....linux.org.uk>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	"Luck,Tony" <tony.luck@...el.com>, PaulMundt <lethal@...ux-sh.org>,
	Chris Metcalf <cmetcalf@...era.com>
Subject: Re: [PATCH 06/17] arm: mmu_gather rework

On Mon, Feb 28, 2011 at 03:18:47PM +0100, Peter Zijlstra wrote:
> On Mon, 2011-02-28 at 12:44 +0100, Peter Zijlstra wrote:
> >   unmap_region()
> >     tlb_gather_mmu()
> >     unmap_vmas()
> >       for (; vma; vma = vma->vm_next)
> >         unmao_page_range()
> >           tlb_start_vma() -> flush cache range
> 
> So why is this correct? Can't we race with a concurrent access to the
> memory region (munmap() vs other thread access race)? While
> unmap_region() callers will have removed the vma from the tree so faults
> will not be satisfied, TLBs might still be present and allow us to
> access the memory and thereby reloading it in the cache.

It is my understanding that code sections between tlb_gather_mmu() and
tlb_finish_mmu() are non-preemptible - that was the case once upon a
time when this stuff first appeared.  If that's changed then that
change has introduced an unnoticed bug.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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