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[67.231.145.42]) by mx.google.com with ESMTPS id i8si23338646pgs.220.2019.06.04.19.45.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 04 Jun 2019 19:45:02 -0700 (PDT) Received-SPF: pass (google.com: domain of prvs=10599ee021=guro@fb.com designates 67.231.145.42 as permitted sender) client-ip=67.231.145.42; Authentication-Results: mx.google.com; dkim=pass header.i=@fb.com header.s=facebook header.b=ZH2TXFP5; spf=pass (google.com: domain of prvs=10599ee021=guro@fb.com designates 67.231.145.42 as permitted sender) smtp.mailfrom="prvs=10599ee021=guro@fb.com"; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=fb.com Received: from pps.filterd (m0044012.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x552j059031912 for ; Tue, 4 Jun 2019 19:45:01 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-type; s=facebook; bh=nRQ8E2xsdPMn6A3dTdY86dEXrfQWn/mxew8g7sZDO2Y=; b=ZH2TXFP5HplCQcFb8fKTo705zDaomejANIkeVDEfi+eT9bkz/E/mo6EKWMQJWSm56Wop t6J0TxVTU+IuYGg522NC14setthkTEunGANNRnhXr+tpOQCz+p96U+h/61T3qcq7ATFn yhr6xk7Vm4ohJ6zLtKK9Z41q5ZPwiRPycHg= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 2swx191ck2-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 04 Jun 2019 19:45:01 -0700 Received: from mx-out.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::6) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1713.5; Tue, 4 Jun 2019 19:44:59 -0700 Received: by devvm2643.prn2.facebook.com (Postfix, from userid 111017) id 7928012C7FDC2; Tue, 4 Jun 2019 19:44:58 -0700 (PDT) Smtp-Origin-Hostprefix: devvm From: Roman Gushchin Smtp-Origin-Hostname: devvm2643.prn2.facebook.com To: Andrew Morton CC: , , , Johannes Weiner , Shakeel Butt , Vladimir Davydov , Waiman Long , Roman Gushchin Smtp-Origin-Cluster: prn2c23 Subject: [PATCH v6 01/10] mm: add missing smp read barrier on getting memcg kmem_cache pointer Date: Tue, 4 Jun 2019 19:44:45 -0700 Message-ID: <20190605024454.1393507-2-guro@fb.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190605024454.1393507-1-guro@fb.com> References: <20190605024454.1393507-1-guro@fb.com> X-FB-Internal: Safe MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-05_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906050015 X-FB-Internal: deliver X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Johannes noticed that reading the memcg kmem_cache pointer in cache_from_memcg_idx() is performed using READ_ONCE() macro, which doesn't implement a SMP barrier, which is required by the logic. Add a proper smp_rmb() to be paired with smp_wmb() in memcg_create_kmem_cache(). The same applies to memcg_create_kmem_cache() itself, which reads the same value without barriers and READ_ONCE(). Suggested-by: Johannes Weiner Signed-off-by: Roman Gushchin --- mm/slab.h | 1 + mm/slab_common.c | 3 ++- 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/slab.h b/mm/slab.h index 739099af6cbb..1176b61bb8fc 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -260,6 +260,7 @@ cache_from_memcg_idx(struct kmem_cache *s, int idx) * memcg_caches issues a write barrier to match this (see * memcg_create_kmem_cache()). */ + smp_rmb(); cachep = READ_ONCE(arr->entries[idx]); rcu_read_unlock(); diff --git a/mm/slab_common.c b/mm/slab_common.c index 58251ba63e4a..8092bdfc05d5 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -652,7 +652,8 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg, * allocation (see memcg_kmem_get_cache()), several threads can try to * create the same cache, but only one of them may succeed. */ - if (arr->entries[idx]) + smp_rmb(); + if (READ_ONCE(arr->entries[idx])) goto out_unlock; cgroup_name(css->cgroup, memcg_name_buf, sizeof(memcg_name_buf)); -- 2.20.1