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    Subject[PATCH 4.7 047/184] pNFS: Ensure LAYOUTGET and LAYOUTRETURN are properly serialised
    Date
    4.7-stable review patch.  If anyone has any objections, please let me know.

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

    From: Trond Myklebust <trond.myklebust@primarydata.com>

    commit bf0291dd2267a2b9a4cd74d65249553d11bb45d6 upstream.

    According to RFC5661, the client is responsible for serialising
    LAYOUTGET and LAYOUTRETURN to avoid ambiguity. Consider the case
    where we send both in parallel.

    Client Server
    ====== ======
    LAYOUTGET(seqid=X)
    LAYOUTRETURN(seqid=X)
    LAYOUTGET return seqid=X+1
    LAYOUTRETURN return seqid=X+2
    Process LAYOUTRETURN
    Forget layout stateid
    Process LAYOUTGET
    Set seqid=X+1

    The client processes the layoutget/layoutreturn in the wrong order,
    and since the result of the layoutreturn was to clear the only
    existing layout segment, the client forgets the layout stateid.

    When the LAYOUTGET comes in, it is treated as having a completely
    new stateid, and so the client sets the wrong sequence id...

    Fix is to check if there are outstanding LAYOUTGET requests
    before we send the LAYOUTRETURN (note that LAYOUGET will already
    wait if it sees an outstanding LAYOUTRETURN).

    Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
    Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/nfs/pnfs.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/fs/nfs/pnfs.c
    +++ b/fs/nfs/pnfs.c
    @@ -876,6 +876,9 @@ void pnfs_clear_layoutreturn_waitbit(str
    static bool
    pnfs_prepare_layoutreturn(struct pnfs_layout_hdr *lo)
    {
    + /* Serialise LAYOUTGET/LAYOUTRETURN */
    + if (atomic_read(&lo->plh_outstanding) != 0)
    + return false;
    if (test_and_set_bit(NFS_LAYOUT_RETURN, &lo->plh_flags))
    return false;
    lo->plh_return_iomode = 0;

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