From: Theodore Ts'o <tytso@mit.edu>
To: Matthew Wilcox <matthew@wil.cx>
Cc: Dave Chinner <david@fromorbit.com>,
Matthew Wilcox <matthew.r.wilcox@intel.com>,
linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 0/3] Add XIP support to ext4
Date: Thu, 19 Dec 2013 00:43:03 -0500 [thread overview]
Message-ID: <20131219054303.GA4391@thunk.org> (raw)
In-Reply-To: <20131219041240.GA19166@parisc-linux.org>
On Wed, Dec 18, 2013 at 09:12:41PM -0700, Matthew Wilcox wrote:
> Now that I've spent the best part of a day looking at the ext4 code, I
> still don't think there's a problem here. With the way the XIP code is
> currently written (calling ext4_get_block with create=1), we won't get an
> uninitialised extent in the caller. Instead, we'll get one that's been
> zeroed (the zeroing is part of patch 3/3 and done only for xip files).
If the block was originally allocated via fallocate(2), it will be
marked as uninitialized. When you call ext4_get_block(), if the block
has been allocated, it will be returned --- and ext4_map_block() as
called by ext4_get_block() does ****not*** clear the uninitialized
flag. It can't do so because it would be racy; you can only clear the
flag once the data blocks has been written.
As far as patch 3/3, it clears the pages in the page cache, but it
doesn't zap them in the XIP storage device. But it only does this on
the code path when it allocated a block. But if the block has already
been previously mapped via fallocate(2), you never hit this section of
code.
Regards,
- Ted
next prev parent reply other threads:[~2013-12-19 5:43 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-17 19:18 [PATCH v3 0/3] Add XIP support to ext4 Matthew Wilcox
2013-12-17 19:18 ` [PATCH v3 1/3] Fix XIP fault vs truncate race Matthew Wilcox
2013-12-17 19:18 ` [PATCH v3 2/3] xip: Add xip_zero_page_range Matthew Wilcox
2013-12-17 19:18 ` [PATCH v3 3/3] ext4: Add XIP functionality Matthew Wilcox
2013-12-17 22:30 ` [PATCH v3 0/3] Add XIP support to ext4 Dave Chinner
2013-12-18 2:31 ` Matthew Wilcox
2013-12-18 5:01 ` Theodore Ts'o
2013-12-18 14:27 ` Matthew Wilcox
2013-12-19 2:07 ` Theodore Ts'o
2013-12-19 4:12 ` Matthew Wilcox
2013-12-19 4:37 ` Dave Chinner
2013-12-19 5:43 ` Theodore Ts'o [this message]
2013-12-19 15:20 ` Matthew Wilcox
2013-12-19 16:17 ` Theodore Ts'o
2013-12-19 17:12 ` Matthew Wilcox
2013-12-19 17:18 ` Theodore Ts'o
2013-12-20 18:17 ` Matthew Wilcox
2013-12-20 19:34 ` Theodore Ts'o
2013-12-20 20:11 ` Matthew Wilcox
2013-12-23 3:36 ` Dave Chinner
2013-12-23 3:45 ` Matthew Wilcox
2013-12-23 4:32 ` Dave Chinner
2013-12-23 6:56 ` Dave Chinner
2013-12-23 14:51 ` Theodore Ts'o
2013-12-23 3:16 ` Dave Chinner
2013-12-24 16:27 ` Matthew Wilcox
2013-12-18 12:33 ` Dave Chinner
2013-12-18 15:22 ` Matthew Wilcox
2013-12-19 0:48 ` Dave Chinner
2013-12-19 1:05 ` Matthew Wilcox
2013-12-19 1:58 ` Dave Chinner
2013-12-19 15:32 ` Matthew Wilcox
2013-12-19 23:46 ` Dave Chinner
2013-12-20 16:45 ` Matthew Wilcox
2013-12-23 4:14 ` Dave Chinner
2013-12-18 18:13 ` Eric Sandeen
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