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    Subject[PATCH 4.19 39/44] libceph: avoid KEEPALIVE_PENDING races in ceph_con_keepalive()
    Date
    4.19-stable review patch.  If anyone has any objections, please let me know.

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

    From: Ilya Dryomov <idryomov@gmail.com>

    commit 4aac9228d16458cedcfd90c7fb37211cf3653ac3 upstream.

    con_fault() can transition the connection into STANDBY right after
    ceph_con_keepalive() clears STANDBY in clear_standby():

    libceph user thread ceph-msgr worker

    ceph_con_keepalive()
    mutex_lock(&con->mutex)
    clear_standby(con)
    mutex_unlock(&con->mutex)
    mutex_lock(&con->mutex)
    con_fault()
    ...
    if KEEPALIVE_PENDING isn't set
    set state to STANDBY
    ...
    mutex_unlock(&con->mutex)
    set KEEPALIVE_PENDING
    set WRITE_PENDING

    This triggers warnings in clear_standby() when either ceph_con_send()
    or ceph_con_keepalive() get to clearing STANDBY next time.

    I don't see a reason to condition queue_con() call on the previous
    value of KEEPALIVE_PENDING, so move the setting of KEEPALIVE_PENDING
    into the critical section -- unlike WRITE_PENDING, KEEPALIVE_PENDING
    could have been a non-atomic flag.

    Reported-by: syzbot+acdeb633f6211ccdf886@syzkaller.appspotmail.com
    Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
    Tested-by: Myungho Jung <mhjungk@gmail.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/ceph/messenger.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/net/ceph/messenger.c
    +++ b/net/ceph/messenger.c
    @@ -3240,9 +3240,10 @@ void ceph_con_keepalive(struct ceph_conn
    dout("con_keepalive %p\n", con);
    mutex_lock(&con->mutex);
    clear_standby(con);
    + con_flag_set(con, CON_FLAG_KEEPALIVE_PENDING);
    mutex_unlock(&con->mutex);
    - if (con_flag_test_and_set(con, CON_FLAG_KEEPALIVE_PENDING) == 0 &&
    - con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
    +
    + if (con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
    queue_con(con);
    }
    EXPORT_SYMBOL(ceph_con_keepalive);

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