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    Subject[PATCH 4.14 106/167] ext4: fix a race in the ext4 shutdown path
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Harshad Shirwadkar <harshads@google.com>

    commit abbc3f9395c76d554a9ed27d4b1ebfb5d9b0e4ca upstream.

    This patch fixes a race between the shutdown path and bio completion
    handling. In the ext4 direct io path with async io, after submitting a
    bio to the block layer, if journal starting fails,
    ext4_direct_IO_write() would bail out pretending that the IO
    failed. The caller would have had no way of knowing whether or not the
    IO was successfully submitted. So instead, we return -EIOCBQUEUED in
    this case. Now, the caller knows that the IO was submitted. The bio
    completion handler takes care of the error.

    Tested: Ran the shutdown xfstest test 461 in loop for over 2 hours across
    4 machines resulting in over 400 runs. Verified that the race didn't
    occur. Usually the race was seen in about 20-30 iterations.

    Signed-off-by: Harshad Shirwadkar <harshads@google.com>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Cc: stable@vger.kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ext4/inode.c | 16 ++++++++++++----
    1 file changed, 12 insertions(+), 4 deletions(-)

    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -3724,10 +3724,18 @@ static ssize_t ext4_direct_IO_write(stru
    /* Credits for sb + inode write */
    handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
    if (IS_ERR(handle)) {
    - /* This is really bad luck. We've written the data
    - * but cannot extend i_size. Bail out and pretend
    - * the write failed... */
    - ret = PTR_ERR(handle);
    + /*
    + * We wrote the data but cannot extend
    + * i_size. Bail out. In async io case, we do
    + * not return error here because we have
    + * already submmitted the corresponding
    + * bio. Returning error here makes the caller
    + * think that this IO is done and failed
    + * resulting in race with bio's completion
    + * handler.
    + */
    + if (!ret)
    + ret = PTR_ERR(handle);
    if (inode->i_nlink)
    ext4_orphan_del(NULL, inode);


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