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From: Takeshi Yoshimura <t.yoshimura8869@gmail.com>
To: dev@dpdk.org
Cc: Takeshi Yoshimura <t.yoshimura8869@gmail.com>,
	stable@dpdk.org, Takeshi Yoshimura <tyos@jp.ibm.com>
Subject: [dpdk-dev] [PATCH] rte_ring: fix racy dequeue/enqueue in ppc64
Date: Thu, 12 Jul 2018 11:44:14 +0900
Message-ID: <20180712024414.4756-1-t.yoshimura8869@gmail.com> (raw)

SPDK blobfs encountered a crash around rte_ring dequeues in ppc64.
It uses a single consumer and multiple producers for a rte_ring.
The problem was a load-load reorder in rte_ring_sc_dequeue_bulk().

The reordered loads happened on r->prod.tail in
__rte_ring_move_cons_head() (rte_ring_generic.h) and ring[idx] in
DEQUEUE_PTRS() (rte_ring.h). They have a load-load control
dependency, but the code does not satisfy it. Note that they are
not reordered if __rte_ring_move_cons_head() with is_sc != 1 because
cmpset invokes a read barrier.

The paired stores on these loads are in ENQUEUE_PTRS() and
update_tail(). Simplified code around the reorder is the following.

Consumer             Producer
load idx[ring]
                     store idx[ring]
                     store r->prod.tail
load r->prod.tail

In this case, the consumer loads old idx[ring] and confirms the load
is valid with the new r->prod.tail.

I added a read barrier in the case where __IS_SC is passed to
__rte_ring_move_cons_head(). I also fixed __rte_ring_move_prod_head()
to avoid similar problems with a single producer.

Cc: stable@dpdk.org

Signed-off-by: Takeshi Yoshimura <tyos@jp.ibm.com>
---
 lib/librte_ring/rte_ring_generic.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/librte_ring/rte_ring_generic.h b/lib/librte_ring/rte_ring_generic.h
index ea7dbe5b9..477326180 100644
--- a/lib/librte_ring/rte_ring_generic.h
+++ b/lib/librte_ring/rte_ring_generic.h
@@ -90,9 +90,10 @@ __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
 			return 0;
 
 		*new_head = *old_head + n;
-		if (is_sp)
+		if (is_sp) {
+			rte_smp_rmb();
 			r->prod.head = *new_head, success = 1;
-		else
+		} else
 			success = rte_atomic32_cmpset(&r->prod.head,
 					*old_head, *new_head);
 	} while (unlikely(success == 0));
@@ -158,9 +159,10 @@ __rte_ring_move_cons_head(struct rte_ring *r, unsigned int is_sc,
 			return 0;
 
 		*new_head = *old_head + n;
-		if (is_sc)
+		if (is_sc) {
+			rte_smp_rmb();
 			r->cons.head = *new_head, success = 1;
-		else
+		} else
 			success = rte_atomic32_cmpset(&r->cons.head, *old_head,
 					*new_head);
 	} while (unlikely(success == 0));
-- 
2.17.1

             reply	other threads:[~2018-07-12  2:44 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-12  2:44 Takeshi Yoshimura [this message]
2018-07-12 17:08 ` Jerin Jacob
2018-07-17  2:54   ` Takeshi Yoshimura
2018-07-17  3:34     ` Jerin Jacob
2021-03-24 21:45       ` [dpdk-dev] [dpdk-stable] " Thomas Monjalon
2021-03-28  1:00         ` Honnappa Nagarahalli
2021-06-16  7:14           ` [dpdk-dev] 回复: " Feifei Wang
2021-06-16 16:37             ` [dpdk-dev] " Honnappa Nagarahalli

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