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GET /api/patches/75983/?format=api
{ "id": 75983, "url": "http://patchwork.dpdk.org/api/patches/75983/?format=api", "web_url": "http://patchwork.dpdk.org/project/dpdk/patch/20200826092002.19395-1-diogo.behrens@huawei.com/", "project": { "id": 1, "url": "http://patchwork.dpdk.org/api/projects/1/?format=api", "name": "DPDK", "link_name": "dpdk", "list_id": "dev.dpdk.org", "list_email": "dev@dpdk.org", "web_url": "http://core.dpdk.org", "scm_url": "git://dpdk.org/dpdk", "webscm_url": "http://git.dpdk.org/dpdk", "list_archive_url": "https://inbox.dpdk.org/dev", "list_archive_url_format": "https://inbox.dpdk.org/dev/{}", "commit_url_format": "" }, "msgid": "<20200826092002.19395-1-diogo.behrens@huawei.com>", "list_archive_url": "https://inbox.dpdk.org/dev/20200826092002.19395-1-diogo.behrens@huawei.com", "date": "2020-08-26T09:20:02", "name": "librte_eal: fix mcslock hang on weak memory", "commit_ref": null, "pull_url": null, "state": "accepted", "archived": true, "hash": "04f34407279a636a440dc6083553316b7ec65c22", "submitter": { "id": 1937, "url": "http://patchwork.dpdk.org/api/people/1937/?format=api", "name": "Diogo Behrens", "email": "diogo.behrens@huawei.com" }, "delegate": { "id": 1, "url": "http://patchwork.dpdk.org/api/users/1/?format=api", "username": "tmonjalo", "first_name": "Thomas", "last_name": "Monjalon", "email": "thomas@monjalon.net" }, "mbox": "http://patchwork.dpdk.org/project/dpdk/patch/20200826092002.19395-1-diogo.behrens@huawei.com/mbox/", "series": [ { "id": 11799, "url": "http://patchwork.dpdk.org/api/series/11799/?format=api", "web_url": "http://patchwork.dpdk.org/project/dpdk/list/?series=11799", "date": "2020-08-26T09:20:02", "name": "librte_eal: fix mcslock hang on weak memory", "version": 1, "mbox": "http://patchwork.dpdk.org/series/11799/mbox/" } ], "comments": "http://patchwork.dpdk.org/api/patches/75983/comments/", "check": "success", "checks": "http://patchwork.dpdk.org/api/patches/75983/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<dev-bounces@dpdk.org>", "X-Original-To": "patchwork@inbox.dpdk.org", "Delivered-To": "patchwork@inbox.dpdk.org", "Received": [ "from dpdk.org (dpdk.org [92.243.14.124])\n\tby inbox.dpdk.org (Postfix) with ESMTP id 28E66A04B1;\n\tWed, 26 Aug 2020 11:20:38 +0200 (CEST)", "from [92.243.14.124] (localhost [127.0.0.1])\n\tby dpdk.org (Postfix) with ESMTP id 73EF44F9C;\n\tWed, 26 Aug 2020 11:20:37 +0200 (CEST)", "from huawei.com (lhrrgout.huawei.com [185.176.76.210])\n by dpdk.org (Postfix) with ESMTP id CC6E41F1C\n for <dev@dpdk.org>; Wed, 26 Aug 2020 11:20:35 +0200 (CEST)", "from lhreml728-chm.china.huawei.com (unknown [172.18.7.106])\n by Forcepoint Email with ESMTP id 1E0625CE3FFC13825177;\n Wed, 26 Aug 2020 10:20:34 +0100 (IST)", "from debian.fritz.box (10.198.195.7) by\n lhreml728-chm.china.huawei.com (10.201.108.79) with Microsoft SMTP Server\n (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id\n 15.1.1913.5; Wed, 26 Aug 2020 10:20:16 +0100" ], "From": "Diogo Behrens <diogo.behrens@huawei.com>", "To": "Phil Yang <phil.yang@arm.com>", "CC": "<dev@dpdk.org>", "Date": "Wed, 26 Aug 2020 11:20:02 +0200", "Message-ID": "<20200826092002.19395-1-diogo.behrens@huawei.com>", "X-Mailer": "git-send-email 2.28.0", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "Content-Type": "text/plain", "X-Originating-IP": "[10.198.195.7]", "X-ClientProxiedBy": "lhreml727-chm.china.huawei.com (10.201.108.78) To\n lhreml728-chm.china.huawei.com (10.201.108.79)", "X-CFilter-Loop": "Reflected", "Subject": "[dpdk-dev] [PATCH] librte_eal: fix mcslock hang on weak memory", "X-BeenThere": "dev@dpdk.org", "X-Mailman-Version": "2.1.15", "Precedence": "list", "List-Id": "DPDK patches and discussions <dev.dpdk.org>", "List-Unsubscribe": "<https://mails.dpdk.org/options/dev>,\n <mailto:dev-request@dpdk.org?subject=unsubscribe>", "List-Archive": "<http://mails.dpdk.org/archives/dev/>", "List-Post": "<mailto:dev@dpdk.org>", "List-Help": "<mailto:dev-request@dpdk.org?subject=help>", "List-Subscribe": "<https://mails.dpdk.org/listinfo/dev>,\n <mailto:dev-request@dpdk.org?subject=subscribe>", "Errors-To": "dev-bounces@dpdk.org", "Sender": "\"dev\" <dev-bounces@dpdk.org>" }, "content": "The initialization me->locked=1 in lock() must happen before\n next->locked=0 in unlock(), otherwise a thread may hang forever,\n waiting me->locked become 0. On weak memory systems (such as ARMv8),\n the current implementation allows me->locked=1 to be reordered with\n announcing the node (pred->next=me) and, consequently, to be\n reordered with next->locked=0 in unlock().\n\n This fix adds a release barrier to pred->next=me, forcing\n me->locked=1 to happen before this operation.\n\nSigned-off-by: Diogo Behrens <diogo.behrens@huawei.com>\n---\n lib/librte_eal/include/generic/rte_mcslock.h | 9 ++++++++-\n 1 file changed, 8 insertions(+), 1 deletion(-)", "diff": "diff --git a/lib/librte_eal/include/generic/rte_mcslock.h b/lib/librte_eal/include/generic/rte_mcslock.h\nindex 2bef28351..ce553f547 100644\n--- a/lib/librte_eal/include/generic/rte_mcslock.h\n+++ b/lib/librte_eal/include/generic/rte_mcslock.h\n@@ -68,7 +68,14 @@ rte_mcslock_lock(rte_mcslock_t **msl, rte_mcslock_t *me)\n \t\t */\n \t\treturn;\n \t}\n-\t__atomic_store_n(&prev->next, me, __ATOMIC_RELAXED);\n+\t/* The store to me->next above should also complete before the node is\n+\t * visible to predecessor thread releasing the lock. Hence, the store\n+\t * prev->next also requires release semantics. Note that, for example,\n+\t * on ARM, the release semantics in the exchange operation is not\n+\t * strong as a release fence and is not sufficient to enforce the\n+\t * desired order here.\n+\t */\n+\t__atomic_store_n(&prev->next, me, __ATOMIC_RELEASE);\n \n \t/* The while-load of me->locked should not move above the previous\n \t * store to prev->next. Otherwise it will cause a deadlock. Need a\n", "prefixes": [] }