From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com (foss.arm.com [217.140.101.70]) by dpdk.org (Postfix) with ESMTP id 591BF4C95; Tue, 12 Mar 2019 17:59:09 +0100 (CET) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B25D115AB; Tue, 12 Mar 2019 09:59:08 -0700 (PDT) Received: from net-arm-thunderx2.shanghai.arm.com (net-arm-thunderx2.shanghai.arm.com [10.169.40.121]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id BE85B3F59C; Tue, 12 Mar 2019 09:59:06 -0700 (PDT) From: Gavin Hu To: dev@dpdk.org Cc: nd@arm.com, gavin hu , thomas@monjalon.net, konstantin.ananyev@intel.com, jerinj@marvell.com, hemant.agrawal@nxp.com, nipun.gupta@nxp.com, Honnappa.Nagarahalli@arm.com, i.maximets@samsung.com, chaozhu@linux.vnet.ibm.com, stable@dpdk.org Date: Wed, 13 Mar 2019 00:58:53 +0800 Message-Id: <1552409933-45684-2-git-send-email-gavin.hu@arm.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1552409933-45684-1-git-send-email-gavin.hu@arm.com> References: <1552409933-45684-1-git-send-email-gavin.hu@arm.com> In-Reply-To: <1551841661-42892-1-git-send-email-gavin.hu@arm.com> References: <1551841661-42892-1-git-send-email-gavin.hu@arm.com> Subject: [dpdk-stable] [PATCH v3 1/1] ring: enforce reading the tail before reading ring slots X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches for DPDK stable branches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 12 Mar 2019 16:59:09 -0000 From: gavin hu In weak memory models, like arm64, reading the prod.tail may get reordered after reading the ring slots, which corrupts the ring and stale data is observed. This issue was reported by NXP on 8-A72 DPAA2 board. The problem is most likely caused by missing the acquire semantics when reading prod.tail (in SC dequeue) which makes it possible to read a stale value from the ring slots. For MP (and MC) case, rte_atomic32_cmpset() already provides the required ordering. For SP case, the control depependency between if-statement(which depends on the read of r->cons.tail) and the later stores to the ring slots make RMB unnecessary. About the control dependency, read more at: https://www.cl.cam.ac.uk/~pes20/ppc-supplemental/test7.pdf This patch is adding the required read barrier to prevent reading the ring slots get reordered before reading prod.tail for SC case. Fixes: c9fb3c62896f ("ring: move code in a new header file") Cc: stable@dpdk.org Signed-off-by: gavin hu Reviewed-by: Ola Liljedahl Tested-by: Nipun Gupta --- lib/librte_ring/rte_ring_generic.h | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/lib/librte_ring/rte_ring_generic.h b/lib/librte_ring/rte_ring_generic.h index ea7dbe5..953cdbb 100644 --- a/lib/librte_ring/rte_ring_generic.h +++ b/lib/librte_ring/rte_ring_generic.h @@ -158,11 +158,14 @@ __rte_ring_move_cons_head(struct rte_ring *r, unsigned int is_sc, return 0; *new_head = *old_head + n; - if (is_sc) - r->cons.head = *new_head, success = 1; - else + if (is_sc) { + r->cons.head = *new_head; + rte_smp_rmb(); + success = 1; + } else { success = rte_atomic32_cmpset(&r->cons.head, *old_head, *new_head); + } } while (unlikely(success == 0)); return n; } -- 2.7.4