From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Andrew Morton <akpm@osdl.org>
Cc: Hugh Dickins <hugh@veritas.com>,
Linux Memory Management <linux-mm@kvack.org>,
Ralf Baechle <ralf@linux-mips.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [patch] mm: mremap correct rmap accounting
Date: Mon, 29 Jan 2007 17:57:37 +1100 [thread overview]
Message-ID: <45BD9AE1.6000501@yahoo.com.au> (raw)
In-Reply-To: <20070128224002.3e7da788.akpm@osdl.org>
Andrew Morton wrote:
> On Mon, 29 Jan 2007 14:31:07 +1100
> Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
>
>>When mremap()ing virtual addresses, some architectures (read: MIPS) switches
>>underlying pages if encountering ZERO_PAGE(old_vaddr) != ZERO_PAGE(new_vaddr).
>>
>>The problem is that the refcount and mapcount remain on the old page, while
>>the actual pte is switched to the new one. This would counter underruns and
>>confuse the rmap code.
>
>
> umm, that sounds fairly fatal. For how long has this bug been present?
>
It would be. We have a catch to prevent ZERO_PAGE from actually getting freed,
but it would spew warnings and eventually go bug in the page_mapcount underflow
check.
It has been around for quite a few releases, so either we don't have many R4000
or R4400 SC and MC CPUs running a recent kernel, or this type of mremap is
pretty rare, or both. We get far more reports of mapcount underflow on x86 than
MIPS!
If Ralf acks then I think it could go into the next release.
--
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next prev parent reply other threads:[~2007-01-29 6:57 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-23 14:19 [patch] mm: mremap correct rmap accounting Nick Piggin
2007-01-23 20:55 ` Hugh Dickins
2007-01-23 23:49 ` Nick Piggin
2007-01-29 3:31 ` Nick Piggin
2007-01-29 6:40 ` Andrew Morton
2007-01-29 6:57 ` Nick Piggin [this message]
2007-01-29 19:08 ` Hugh Dickins
2007-01-29 19:27 ` Linus Torvalds
2007-01-29 20:03 ` Andrew Morton
2007-01-29 20:18 ` Linus Torvalds
2007-01-29 21:27 ` Ralf Baechle
2007-01-29 20:10 ` Hugh Dickins
2007-01-29 20:22 ` Linus Torvalds
2007-01-29 20:38 ` Hugh Dickins
2007-01-29 21:24 ` Hugh Dickins
2007-01-30 1:00 ` Nick Piggin
2007-01-30 14:24 ` Carsten Otte
2007-01-30 16:41 ` Ralf Baechle
2007-01-30 17:35 ` Carsten Otte
2007-01-30 15:47 ` Carsten Otte
2007-01-30 22:04 ` Hugh Dickins
2007-01-31 13:51 ` Carsten Otte
2007-01-31 13:59 ` Carsten Otte
2007-01-31 16:31 ` Hugh Dickins
2007-02-01 16:21 ` Carsten Otte
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