From: jiayingz@google.com (Jiaying Zhang) Subject: [PATCH] ext4: Flush any pending end_io requests before O_direct read on dioread_nolock Date: Thu, 18 Aug 2011 18:28:45 -0700 (PDT) Message-ID: <20110819012845.7A4A32012F@ruihe2.smo.corp.google.com> Cc: linux-ext4@vger.kernel.org To: tytso@mit.edu Return-path: Received: from smtp-out.google.com ([216.239.44.51]:47250 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751906Ab1HSB2s (ORCPT ); Thu, 18 Aug 2011 21:28:48 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: 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 --- fs/ext4/indirect.c | 9 +++++++-- 1 files changed, 7 insertions(+), 2 deletions(-) diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c index 6c27111..ca90d73 100644 --- a/fs/ext4/indirect.c +++ b/fs/ext4/indirect.c @@ -800,12 +800,17 @@ ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb, } retry: - if (rw == READ && ext4_should_dioread_nolock(inode)) + if (rw == READ && ext4_should_dioread_nolock(inode)) { + if (unlikely(!list_empty(&ei->i_completed_io_list))) { + mutex_lock(&inode->i_mutex); + ext4_flush_completed_IO(inode); + mutex_unlock(&inode->i_mutex); + } ret = __blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov, offset, nr_segs, ext4_get_block, NULL, NULL, 0); - else { + } else { ret = blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov, offset, nr_segs, -- 1.7.3.1