From: Hugh Dickins <hughd@google.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: akpm@linux-foundation.org, robert@swiecki.net,
lkml20101129@newton.leun.net, linux-kernel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: kernel BUG at mm/truncate.c:475!
Date: Wed, 15 Dec 2010 16:26:11 -0800 (PST) [thread overview]
Message-ID: <alpine.LSU.2.00.1012151542480.7987@tigran.mtv.corp.google.com> (raw)
In-Reply-To: <E1PSpQw-0005s5-QW@pomaz-ex.szeredi.hu>
On Wed, 15 Dec 2010, Miklos Szeredi wrote:
> On Tue, 14 Dec 2010, Hugh Dickins wrote:
> > I'd feel rather happier about it if I thought it would also fix
> > Robert's kernel BUG at /build/buildd/linux-2.6.35/mm/filemap.c:128!
> > but I've still not found time to explain that one.
>
> Me neither, all unmap_mapping_range() calls from shmfs are either with
> i_mutex or from evict_inode.
And the page returned by shmem_fault is already locked.
>
> Hmm, is there anything preventing remap_file_pages() installing a pte
> at an address that unmap_mapping_range() has already processed?
Interesting line of thought: nothing I think, but isn't that okay?
Though its zap_pte can take out present ptes pointing to actual pages,
all populate_range ever installs is non-present pte_file entries: and a
fault on one of those goes through the same checks as in a linear mapping.
(I thought I was going to find an inconsistency with zap_pte_range there,
but no: truncation does not remove pte_file entries beyond end of file,
I remember now thinking that we need to keep SIGBUS-beyond-EOF on them,
instead of letting truncation silently revert those offsets to linear.)
Or am I missing something?
(Well, we know I am, because I've not explained Robert's BUG.)
Hugh
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next prev parent reply other threads:[~2010-12-16 0:26 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20101130194945.58962c44@xenia.leun.net>
2010-11-30 23:00 ` Hugh Dickins
2010-12-01 10:25 ` Miklos Szeredi
2010-12-01 11:45 ` Michael Leun
2010-12-01 17:22 ` Miklos Szeredi
2010-12-02 7:41 ` Michael Leun
2010-12-02 8:15 ` Michael Leun
2010-12-02 9:42 ` Miklos Szeredi
2010-12-02 10:57 ` Michael Leun
2010-12-03 7:53 ` Michael Leun
2010-12-06 12:36 ` Miklos Szeredi
2010-12-06 19:43 ` Michael Leun
2010-12-11 14:14 ` Miklos Szeredi
2010-12-11 19:50 ` Michael Leun
2010-12-13 22:20 ` Andrew Morton
2010-12-14 7:31 ` Hugh Dickins
2010-12-14 9:10 ` Peter Zijlstra
2010-12-14 9:11 ` Peter Zijlstra
2010-12-14 10:45 ` Miklos Szeredi
2010-12-15 4:32 ` Hugh Dickins
2010-12-15 11:22 ` Miklos Szeredi
2010-12-16 0:26 ` Hugh Dickins [this message]
2010-12-16 14:50 ` Robert Święcki
2010-12-16 19:05 ` Hugh Dickins
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