distributor: fix handshake deadlock

Synchronization of data exchange between distributor and worker cores
is based on 2 handshakes: retptr64 for returning mbufs from workers
to distributor and bufptr64 for passing mbufs to workers.

Without proper order of verifying those 2 handshakes a deadlock may
occur. This can happen when worker core wants to return back mbufs
and waits for retptr handshake to be cleared while distributor core
waits for bufptr to send mbufs to worker.

This can happen as worker core first returns mbufs to distributor
and later gets new mbufs, while distributor first releases mbufs
to worker and later handle returning packets.

This patch fixes possibility of the deadlock by always taking care
of returning packets first on the distributor side and handling
packets while waiting to release new.

Fixes: 775003ad2f96 ("distributor: add new burst-capable library")
Cc: stable@dpdk.org
Signed-off-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>
Acked-by: David Hunt <david.hunt@intel.com>

diff --git a/lib/librte_distributor/rte_distributor.c b/lib/librte_distributor/rte_distributor.c
index c6b19a388649b3e7e3363e34e8ffd3f04d068765..d6d4350a28c78ea35dba35eaf97fa58097842a42 100644 (file)
--- a/lib/librte_distributor/rte_distributor.c
+++ b/lib/librte_distributor/rte_distributor.c
@@ -319,12 +319,14 @@ release(struct rte_distributor *d, unsigned int wkr)
        struct rte_distributor_buffer *buf = &(d->bufs[wkr]);
        unsigned int i;
 
+       handle_returns(d, wkr);
+
        /* Sync with worker on GET_BUF flag */
        while (!(__atomic_load_n(&(d->bufs[wkr].bufptr64[0]), __ATOMIC_ACQUIRE)
-               & RTE_DISTRIB_GET_BUF))
+               & RTE_DISTRIB_GET_BUF)) {
+               handle_returns(d, wkr);
                rte_pause();
-
-       handle_returns(d, wkr);
+       }
 
        buf->count = 0;
 
@@ -374,6 +376,7 @@ rte_distributor_process(struct rte_distributor *d,
                /* Flush out all non-full cache-lines to workers. */
                for (wid = 0 ; wid < d->num_workers; wid++) {
                        /* Sync with worker on GET_BUF flag. */
+                       handle_returns(d, wid);
                        if (__atomic_load_n(&(d->bufs[wid].bufptr64[0]),
                                __ATOMIC_ACQUIRE) & RTE_DISTRIB_GET_BUF) {
                                release(d, wid);