From: Michael Tokarev Subject: Re: what happened with dccaf33fa37 "ext4: flush any pending end_io requests before DIO" for 3.0? Date: Mon, 19 Mar 2012 21:21:51 +0400 Message-ID: <4F676B2F.8040209@msgid.tls.msk.ru> References: <4ED6942F.7070006@msgid.tls.msk.ru> <4F4CBDA1.1080302@msgid.tls.msk.ru> <4F6459F2.8010403@msgid.tls.msk.ru> <20120319164256.GB10561@quack.suse.cz> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------000905030600020105090507" Cc: Theodore Tso , gregkh@linuxfoundation.org, stable@kernel.org, linux-ext4@vger.kernel.org, Theodore Ts'o , Jan Kara To: Jiaying Zhang Return-path: Received: from isrv.corpit.ru ([86.62.121.231]:38910 "EHLO isrv.corpit.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1162030Ab2CSRVx (ORCPT ); Mon, 19 Mar 2012 13:21:53 -0400 In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: This is a multi-part message in MIME format. --------------000905030600020105090507 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 19.03.2012 21:10, Jiaying Zhang wrote: > On Mon, Mar 19, 2012 at 9:42 AM, Jan Kara wrote: >> On Sat 17-03-12 13:31:30, Michael Tokarev wrote: >>> Ping? >>> >>> Maybe just a one-line reply isn't THAT difficult? > Sorry for the slow response. I am not sure what happened to this patch. > Ted, do you know what we need to do to get this patch to the > stable release? For reference, attached is the version I use locally since last August. ... >>>>> There was one more ext4 commit at that time, which made its way into >>>>> stable but this one did not. >>>>> >>>>> I wonder if the reason for that was the fact that it needed a small >>>>> "backport" for 3.0, since in 3.1+ the code has been moved into another >>>>> file, and the context is slightly different. In that case, attached >>>>> is the "backport" which we use with 3.0.x since that time. Thanks, /mjt --------------000905030600020105090507 Content-Type: text/x-diff; name="ext4-flush-any-pending-end_io-requests-before-DIO-reads-w-dioread_nolock-dccaf33fa3.diff" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename*0="ext4-flush-any-pending-end_io-requests-before-DIO-reads-w-di"; filename*1="oread_nolock-dccaf33fa3.diff" (backported to 3.0 by mjt) upstream_commit dccaf33fa37a1bc5d651baeb3bfeb6becb86597b Author: Jiaying Zhang Date: Fri Aug 19 19:13:32 2011 -0400 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 Signed-off-by: "Theodore Ts'o" Signed-off-by: Michael Tokarev Cc: stable@kernel.org diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c index b8602cd..0962642 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -3507,12 +3507,17 @@ 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, --------------000905030600020105090507--