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    Subject[ 081/108] ext4: flush any pending end_io requests before DIO reads w/dioread_nolock
    3.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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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