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Date: Thu, 26 Apr 2001 22:11:09 +0200
From: Andrea Arcangeli <andrea@suse.de>
To: Alexander Viro <viro@math.psu.edu>
Cc: Linus Torvalds <torvalds@transmeta.com>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] SMP race in ext2 - metadata corruption.
Message-ID: <20010426221109.E819@athlon.random>
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In-Reply-To: <Pine.GSO.4.21.0104261554050.15385-100000@weyl.math.psu.edu>; from viro@math.psu.edu on Thu, Apr 26, 2001 at 03:55:19PM -0400
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On Thu, Apr 26, 2001 at 03:55:19PM -0400, Alexander Viro wrote:
> 
> 
> On Thu, 26 Apr 2001, Andrea Arcangeli wrote:
> 
> > On Thu, Apr 26, 2001 at 03:34:00PM -0400, Alexander Viro wrote:
> > > Same scenario, but with read-in-progress started before we do getblk(). BTW,
> > 
> > how can the read in progress see a branch that we didn't spliced yet? We
> 
> fd = open("/dev/hda1", O_RDONLY);
> read(fd, buf, sizeof(buf));

You misunderstood the context of what I said, I perfectly know the race
you are talking about, I was answering Linus's question "the
wait_on_buffer isn't even necessary to protect ext2 against ext2". You
are talking about the other race that is "ext2" against "block_dev", and
I obviously agree on that one since the first place as I immediatly
answered you "correct".

What I'm saying above is that even without the wait_on_buffer ext2 can
screwup itself because the splice happens after the buffer are just all
uptodate so any "reader" (I mean any reader through ext2 not through
block_dev) will never try to do a bread on that blocks before they're
just zeroed and uptodate.

Andrea
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