On Feb 10, 2015, at 9:22 AM, Sowmini Varadhan <sowmini.varad...@oracle.com>
wrote:
>
> This patch fixes a sock_lock deadlock in the rds_cong_queue_update path.
Note that the deadlock appears to exist only with TCP transports.
> We cannot inline the call to rds_send_xmit from rds_cong_queue_update
> because
> (a) we are already holding the sock_lock in the recv path, and
> will deadlock when tcp_setsockopt/tcp_sendmsg try to get the sock
> lock
> (b) cong_queue_update does an irqsave on the rds_cong_lock, and this
> will trigger warnings (for a good reason) from functions called
> out of sock_lock.
>
> Signed-off-by: Sowmini Varadhan <sowmini.varad...@oracle.com>
> ---
> net/rds/cong.c | 16 +++++++++++++++-
> 1 files changed, 15 insertions(+), 1 deletions(-)
>
> diff --git a/net/rds/cong.c b/net/rds/cong.c
> index e5b65ac..765d18f 100644
> --- a/net/rds/cong.c
> +++ b/net/rds/cong.c
> @@ -221,7 +221,21 @@ void rds_cong_queue_updates(struct rds_cong_map *map)
> list_for_each_entry(conn, &map->m_conn_list, c_map_item) {
> if (!test_and_set_bit(0, &conn->c_map_queued)) {
> rds_stats_inc(s_cong_update_queued);
> - rds_send_xmit(conn);
> + /* We cannot inline the call to rds_send_xmit() here
> + * for two reasons:
> + * 1. When we get here from the receive path, we
> + * are already holding the sock_lock (held by
> + * tcp_v4_rcv()). So inlining calls to
> + * tcp_setsockopt and/or tcp_sendmsg will deadlock
> + * when it tries to get the sock_lock())
> + * 2. Interrupts are masked so that we can mark the
> + * the port congested from both send and recv paths.
> + * (See comment around declaration of rds_cong_lock).
> + * An attempt to get the sock_lock() here will
> + * therefore trigger warnings.
> + * Defer the xmit to rds_send_worker() instead.
> + */
> + queue_delayed_work(rds_wq, &conn->c_send_w, 0);
> }
> }
>
> --
> 1.7.1
>
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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