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Date:	Tue, 6 Oct 2015 23:34:48 -0400
From:	Theodore Ts'o <>
To:	Dave Hansen <>
Cc:	Andrew Morton <>,
	Linus Torvalds <>,,
Subject: Re: [REGRESSION] 998ef75ddb and aio-dio-invalidate-failure w/

On Mon, Oct 05, 2015 at 11:04:35AM -0700, Dave Hansen wrote:
> The warning comes out of ext4_walk_page_buffers() and the dirty state
> comes from page_zero_new_buffers(). That seems a _bit_ goofy that the
> filesystem is marking the page dirty and then so shortly warning about it.

Yes, this is a bug in ext4 --- and in fact in ext3, which apparently
we've lived with for *years*.  The problem is that when we are
journalling data buffers, we can't use page_zero_new_buffers(),
because instead of calling mark_buffer_dirty(bh), we need to call
ext4_handle_dirty_metadata(bh).  This will call mark_buffer_dirty(bh)
if journalling is not enabled, or if journalling is enabled, it will
call jbd2_journal_dirty_metadata(handle,bh).

Apprently it is extremely rare that (copied < len) --- especially when
mm/filemap.c was doing a prefault.  :-)

So your patch looks good, but in addition to that, if copied is > 0
and less than len, we shouldn't be calling page_zero_new_buffers().
We're going to need our own version of it that doesn't call

So if Linus wants to revert 998ef75ddb patch, we can do that, but I'm
also happy applying your patch as a way of preventing the failure.
We'll need to do more work to make ext4_journalled_write_end(), but
that's a bigger change which I'd rather not do at this point in the
development cycle.

Thanks again for taking a closer look at things.  I'm currently
running a full soak test to make sure your patch to
ext4_journalled_write_end() doesn't introduce any other problems, but
I'm quite confident it should be fine.


						- Ted
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