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    Subject[PATCH 4.4 264/342] libceph: dont bail early from try_read() when skipping a message
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Ilya Dryomov <idryomov@gmail.com>

    commit e7a88e82fe380459b864e05b372638aeacb0f52d upstream.

    The contract between try_read() and try_write() is that when called
    each processes as much data as possible. When instructed by osd_client
    to skip a message, try_read() is violating this contract by returning
    after receiving and discarding a single message instead of checking for
    more. try_write() then gets a chance to write out more requests,
    generating more replies/skips for try_read() to handle, forcing the
    messenger into a starvation loop.

    Reported-by: Varada Kari <Varada.Kari@sandisk.com>
    Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
    Tested-by: Varada Kari <Varada.Kari@sandisk.com>
    Reviewed-by: Alex Elder <elder@linaro.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/ceph/messenger.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/net/ceph/messenger.c
    +++ b/net/ceph/messenger.c
    @@ -2340,7 +2340,7 @@ static int read_partial_message(struct c
    con->in_base_pos = -front_len - middle_len - data_len -
    sizeof(m->footer);
    con->in_tag = CEPH_MSGR_TAG_READY;
    - return 0;
    + return 1;
    } else if ((s64)seq - (s64)con->in_seq > 1) {
    pr_err("read_partial_message bad seq %lld expected %lld\n",
    seq, con->in_seq + 1);
    @@ -2366,7 +2366,7 @@ static int read_partial_message(struct c
    sizeof(m->footer);
    con->in_tag = CEPH_MSGR_TAG_READY;
    con->in_seq++;
    - return 0;
    + return 1;
    }

    BUG_ON(!con->in_msg);
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