[dpdk-stable] patch 'distributor: fix handshake deadlock' has been queued to stable release 19.11.6

[luca.boccassi at gmail.com]

Hi,

FYI, your patch has been queued to stable release 19.11.6

Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
It will be pushed if I get no objections before 10/30/20. So please
shout if anyone has objections.

Also note that after the patch there's a diff of the upstream commit vs the
patch applied to the branch. This will indicate if there was any rebasing
needed to apply to the stable branch. If there were code changes for rebasing
(ie: not only metadata diffs), please double check that the rebase was
correctly done.

Thanks.

Luca Boccassi

---
>From e5fc315a5f05aaa14b099618a4076d8dcc82f7e1 Mon Sep 17 00:00:00 2001
From: Lukasz Wojciechowski <l.wojciechow at partner.samsung.com>
Date: Sat, 17 Oct 2020 05:06:46 +0200
Subject: [PATCH] distributor: fix handshake deadlock

[ upstream commit 5acce079e7dc773c17bf2043fc18106392b4a863 ]

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")

Signed-off-by: Lukasz Wojciechowski <l.wojciechow at partner.samsung.com>
Acked-by: David Hunt <david.hunt at intel.com>
---
 lib/librte_distributor/rte_distributor.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/librte_distributor/rte_distributor.c b/lib/librte_distributor/rte_distributor.c
index c6b19a3886..d6d4350a28 100644
--- 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);
-- 
2.20.1

---
  Diff of the applied patch vs upstream commit (please double-check if non-empty:
---
--- -	2020-10-28 10:35:17.392993092 +0000
+++ 0183-distributor-fix-handshake-deadlock.patch	2020-10-28 10:35:11.796834322 +0000
@@ -1,8 +1,10 @@
-From 5acce079e7dc773c17bf2043fc18106392b4a863 Mon Sep 17 00:00:00 2001
+From e5fc315a5f05aaa14b099618a4076d8dcc82f7e1 Mon Sep 17 00:00:00 2001
 From: Lukasz Wojciechowski <l.wojciechow at partner.samsung.com>
 Date: Sat, 17 Oct 2020 05:06:46 +0200
 Subject: [PATCH] distributor: fix handshake deadlock
 
+[ upstream commit 5acce079e7dc773c17bf2043fc18106392b4a863 ]
+
 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.
@@ -21,7 +23,6 @@
 packets while waiting to release new.
 
 Fixes: 775003ad2f96 ("distributor: add new burst-capable library")
-Cc: stable at dpdk.org
 
 Signed-off-by: Lukasz Wojciechowski <l.wojciechow at partner.samsung.com>
 Acked-by: David Hunt <david.hunt at intel.com>