| From dccaf33fa37a1bc5d651baeb3bfeb6becb86597b Mon Sep 17 00:00:00 2001 |
| From: Jiaying Zhang <jiayingz@google.com> |
| Date: Fri, 19 Aug 2011 19:13:32 -0400 |
| Subject: ext4: flush any pending end_io requests before DIO reads w/dioread_nolock |
| |
| From: Jiaying Zhang <jiayingz@google.com> |
| |
| commit dccaf33fa37a1bc5d651baeb3bfeb6becb86597b upstream. |
| |
| (backported to 3.0 by mjt) |
| |
| 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: Jan Kara <jack@suse.cz> |
| Signed-off-by: Michael Tokarev <mjt@tls.msk.ru> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| |
| --- |
| fs/ext4/inode.c | 9 +++++++-- |
| 1 file changed, 7 insertions(+), 2 deletions(-) |
| |
| --- a/fs/ext4/inode.c |
| +++ b/fs/ext4/inode.c |
| @@ -3510,12 +3510,17 @@ static ssize_t ext4_ind_direct_IO(int rw |
| } |
| |
| 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, |
