Messages in this thread Patch in this message | | | Date | Fri, 30 Mar 2012 12:58:43 -0700 | From | Greg KH <> | Subject | [ 081/108] ext4: flush any pending end_io requests before DIO reads w/dioread_nolock |
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3.0-stable review patch. If anyone has any objections, please let me know.
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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,
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