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    Subject[PATCH 4.2.y-ckt 203/273] libceph: don't bail early from try_read() when skipping a message
    Date
    4.2.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    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: Kamal Mostafa <kamal@canonical.com>
    ---
    net/ceph/messenger.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
    index ec564c5..1d47fa3 100644
    --- a/net/ceph/messenger.c
    +++ b/net/ceph/messenger.c
    @@ -2328,7 +2328,7 @@ static int read_partial_message(struct ceph_connection *con)
    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);
    @@ -2361,7 +2361,7 @@ static int read_partial_message(struct ceph_connection *con)
    sizeof(m->footer);
    con->in_tag = CEPH_MSGR_TAG_READY;
    con->in_seq++;
    - return 0;
    + return 1;
    }

    BUG_ON(!con->in_msg);
    --
    2.7.0
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