From: Jiaying Zhang <jiayingz@google.com>
Date: Fri, 19 Aug 2011 23:13:32 +0000 (-0400)
Subject: ext4: flush any pending end_io requests before DIO reads w/dioread_nolock
X-Git-Tag: v3.1-rc3~5^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dccaf33fa37a1bc5d651baeb3bfeb6becb86597b;p=pandora-kernel.git

ext4: flush any pending end_io requests before DIO reads w/dioread_nolock

There is a race between ext4 buffer write and direct_IO read with
dioread_nolock mount option enabled. The problem is that we clear
PageWriteback flag during end_io time but will do
uninitialized-to-initialized extent conversion later with dioread_nolock.
If an O_direct read request comes in during this period, ext4 will return
zero instead of the recently written data.

This patch checks whether there are any pending uninitialized-to-initialized
extent conversion requests before doing O_direct read to close the race.
Note that this is just a bandaid fix. The fundamental issue is that we
clear PageWriteback flag before we really complete an IO, which is
problem-prone. To fix the fundamental issue, we may need to implement an
extent tree cache that we can use to look up pending to-be-converted extents.

Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org
---

Reading git-diff-tree failed