From patchwork Fri Oct 2 17:35:53 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Bonzini X-Patchwork-Id: 272163 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43A57C35257 for ; Fri, 2 Oct 2020 17:43:57 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AA6DE20758 for ; Fri, 2 Oct 2020 17:43:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="N0GIfbyI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AA6DE20758 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:45536 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kOP63-0007qi-RK for qemu-devel@archiver.kernel.org; Fri, 02 Oct 2020 13:43:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45028) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kOOyW-0000Ux-82 for qemu-devel@nongnu.org; Fri, 02 Oct 2020 13:36:08 -0400 Received: from mail-wm1-x344.google.com ([2a00:1450:4864:20::344]:52211) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1kOOyU-0003Jj-8v for qemu-devel@nongnu.org; Fri, 02 Oct 2020 13:36:07 -0400 Received: by mail-wm1-x344.google.com with SMTP id w2so2452893wmi.1 for ; Fri, 02 Oct 2020 10:36:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=vBU6G6EU3K8FuII/2jOnVZJBfwDDD7ouVQlKQ+GYXJE=; b=N0GIfbyI7/nweGJQHXHd8QxJIGriJlQQdKUHZHYvP2NhhbTvsMxwGo0Xn0WzkukK7X 30EaIf01UnmUB7fc1B/LVHCqviW8G0DpIO3Rxc5psdhzc+2PHblS52y0Y/aSOijvgN0M HPJJY+y+jwc/xBeSvw0uv+jurLOjXRgiJGLJL829cpugEqsGGyUmixtQVgrEqouEB7Yl WMjYK0Ac1PqQkeraBcFU/wu0ZzJcPyVY8zWAFmyKcOXPo2pAorPfWWnYySOj6CxmW4PV PehP9dIwyoD13g++HmZCk2q9jjKWZjm8K5MEmG2co38u2sukDOX3ofL0vAEWWiV01Tq+ 41wg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:to:cc:subject:date:message-id :in-reply-to:references:mime-version:content-transfer-encoding; bh=vBU6G6EU3K8FuII/2jOnVZJBfwDDD7ouVQlKQ+GYXJE=; b=X+xlMUSyUAf68/OxpbpHd73Op5i/GK+IUcRjPihEP/6HkZkRgm2MI+ZYcvEgNJ9GSL wBReSMtn2gLH0COfKkT35ThCAYrUrgU4YzTjHHLlpDPLopjzxM/UYnDR5fYcwSFX0bJS w7OVS+rPClEjkRgRaZ+dDDqxZG6tlmn0EkRunZzqupnYDEfDKk4zBpMfjDRhOOFY/tHZ og/Tnm8E+BlDxn/5GxSUzGyBmzEukqlev14D/i0EcSPdaBiusNFpHzQLwT3IA0GE2+E/ pGAq0i7JKTt7ABIDoiYS4icDxxtVK4/OcXJuPX4/r9jxfvcCCeeslVOaIi9c3mGpY3Ql 0BhA== X-Gm-Message-State: AOAM531Yk0Hci1jS8fg9nNd9axIzMXmO9LaqMlQTzYJ3WIQ+JKVm1H4O l0sgHNwLS9tgoYsK0bU60c1WCiJKEo8= X-Google-Smtp-Source: ABdhPJyTJmRwDUfcySw//UROlE7h1LhhQvPLoPxoW2d9KHHTWDvGcTL438SZsUR7vuSySJ0rN1fPtg== X-Received: by 2002:a1c:7912:: with SMTP id l18mr4045879wme.124.1601660164500; Fri, 02 Oct 2020 10:36:04 -0700 (PDT) Received: from donizetti.redhat.com ([2001:b07:6468:f312:47e0:e742:75ba:b84d]) by smtp.gmail.com with ESMTPSA id l8sm2516454wrx.22.2020.10.02.10.36.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Oct 2020 10:36:03 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Subject: [PATCH v6 05/10] device-core: use RCU for list of children of a bus Date: Fri, 2 Oct 2020 19:35:53 +0200 Message-Id: <20201002173558.232960-6-pbonzini@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20201002173558.232960-1-pbonzini@redhat.com> References: <20201002173558.232960-1-pbonzini@redhat.com> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::344; envelope-from=paolo.bonzini@gmail.com; helo=mail-wm1-x344.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FORGED_FROMDOMAIN=0.001, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.25, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Stefan Hajnoczi , Maxim Levitsky Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Maxim Levitsky This fixes the race between device emulation code that tries to find a child device to dispatch the request to (e.g a scsi disk), and hotplug of a new device to that bus. Note that this doesn't convert all the readers of the list but only these that might go over that list without BQL held. This is a very small first step to make this code thread safe. Suggested-by: Paolo Bonzini Signed-off-by: Maxim Levitsky Reviewed-by: Stefan Hajnoczi Message-Id: <20200913160259.32145-5-mlevitsk@redhat.com> [Use RCU_READ_LOCK_GUARD in more places, adjust testcase now that the delay in DEVICE_DELETED due to RCU is more consistent. - Paolo] Signed-off-by: Paolo Bonzini --- hw/core/bus.c | 28 ++++++++++++++++----------- hw/core/qdev.c | 37 ++++++++++++++++++++++-------------- hw/scsi/scsi-bus.c | 12 +++++++++--- hw/scsi/virtio-scsi.c | 6 +++++- include/hw/qdev-core.h | 9 +++++++++ tests/qtest/drive_del-test.c | 10 +++------- 6 files changed, 66 insertions(+), 36 deletions(-) diff --git a/hw/core/bus.c b/hw/core/bus.c index 6b987b6946..a0483859ae 100644 --- a/hw/core/bus.c +++ b/hw/core/bus.c @@ -49,12 +49,14 @@ int qbus_walk_children(BusState *bus, } } - QTAILQ_FOREACH(kid, &bus->children, sibling) { - err = qdev_walk_children(kid->child, - pre_devfn, pre_busfn, - post_devfn, post_busfn, opaque); - if (err < 0) { - return err; + WITH_RCU_READ_LOCK_GUARD() { + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { + err = qdev_walk_children(kid->child, + pre_devfn, pre_busfn, + post_devfn, post_busfn, opaque); + if (err < 0) { + return err; + } } } @@ -90,8 +92,10 @@ static void bus_reset_child_foreach(Object *obj, ResettableChildCallback cb, BusState *bus = BUS(obj); BusChild *kid; - QTAILQ_FOREACH(kid, &bus->children, sibling) { - cb(OBJECT(kid->child), opaque, type); + WITH_RCU_READ_LOCK_GUARD() { + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { + cb(OBJECT(kid->child), opaque, type); + } } } @@ -194,9 +198,11 @@ static void bus_set_realized(Object *obj, bool value, Error **errp) /* TODO: recursive realization */ } else if (!value && bus->realized) { - QTAILQ_FOREACH(kid, &bus->children, sibling) { - DeviceState *dev = kid->child; - qdev_unrealize(dev); + WITH_RCU_READ_LOCK_GUARD() { + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { + DeviceState *dev = kid->child; + qdev_unrealize(dev); + } } if (bc->unrealize) { bc->unrealize(bus); diff --git a/hw/core/qdev.c b/hw/core/qdev.c index 74db78df36..59e5e710b7 100644 --- a/hw/core/qdev.c +++ b/hw/core/qdev.c @@ -51,6 +51,12 @@ const VMStateDescription *qdev_get_vmsd(DeviceState *dev) return dc->vmsd; } +static void bus_free_bus_child(BusChild *kid) +{ + object_unref(OBJECT(kid->child)); + g_free(kid); +} + static void bus_remove_child(BusState *bus, DeviceState *child) { BusChild *kid; @@ -60,15 +66,16 @@ static void bus_remove_child(BusState *bus, DeviceState *child) char name[32]; snprintf(name, sizeof(name), "child[%d]", kid->index); - QTAILQ_REMOVE(&bus->children, kid, sibling); + QTAILQ_REMOVE_RCU(&bus->children, kid, sibling); bus->num_children--; /* This gives back ownership of kid->child back to us. */ object_property_del(OBJECT(bus), name); - object_unref(OBJECT(kid->child)); - g_free(kid); - return; + + /* free the bus kid, when it is safe to do so*/ + call_rcu(kid, bus_free_bus_child, rcu); + break; } } } @@ -83,7 +90,7 @@ static void bus_add_child(BusState *bus, DeviceState *child) kid->child = child; object_ref(OBJECT(kid->child)); - QTAILQ_INSERT_HEAD(&bus->children, kid, sibling); + QTAILQ_INSERT_HEAD_RCU(&bus->children, kid, sibling); /* This transfers ownership of kid->child to the property. */ snprintf(name, sizeof(name), "child[%d]", kid->index); @@ -672,17 +679,19 @@ DeviceState *qdev_find_recursive(BusState *bus, const char *id) DeviceState *ret; BusState *child; - QTAILQ_FOREACH(kid, &bus->children, sibling) { - DeviceState *dev = kid->child; + WITH_RCU_READ_LOCK_GUARD() { + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { + DeviceState *dev = kid->child; - if (dev->id && strcmp(dev->id, id) == 0) { - return dev; - } + if (dev->id && strcmp(dev->id, id) == 0) { + return dev; + } - QLIST_FOREACH(child, &dev->child_bus, sibling) { - ret = qdev_find_recursive(child, id); - if (ret) { - return ret; + QLIST_FOREACH(child, &dev->child_bus, sibling) { + ret = qdev_find_recursive(child, id); + if (ret) { + return ret; + } } } } diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c index 69d7c3f90c..4ab9811cd8 100644 --- a/hw/scsi/scsi-bus.c +++ b/hw/scsi/scsi-bus.c @@ -399,7 +399,10 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r) id = r->req.dev->id; found_lun0 = false; n = 0; - QTAILQ_FOREACH(kid, &r->req.bus->qbus.children, sibling) { + + RCU_READ_LOCK_GUARD(); + + QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) { DeviceState *qdev = kid->child; SCSIDevice *dev = SCSI_DEVICE(qdev); @@ -420,7 +423,7 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r) memset(r->buf, 0, len); stl_be_p(&r->buf[0], n); i = found_lun0 ? 8 : 16; - QTAILQ_FOREACH(kid, &r->req.bus->qbus.children, sibling) { + QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) { DeviceState *qdev = kid->child; SCSIDevice *dev = SCSI_DEVICE(qdev); @@ -429,6 +432,7 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r) i += 8; } } + assert(i == n + 8); r->len = len; return true; @@ -1571,7 +1575,8 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun) BusChild *kid; SCSIDevice *target_dev = NULL; - QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) { + RCU_READ_LOCK_GUARD(); + QTAILQ_FOREACH_RCU(kid, &bus->qbus.children, sibling) { DeviceState *qdev = kid->child; SCSIDevice *dev = SCSI_DEVICE(qdev); @@ -1590,6 +1595,7 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun) } } } + return target_dev; } diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c index 3a71ea7097..971afbb217 100644 --- a/hw/scsi/virtio-scsi.c +++ b/hw/scsi/virtio-scsi.c @@ -367,12 +367,16 @@ static int virtio_scsi_do_tmf(VirtIOSCSI *s, VirtIOSCSIReq *req) case VIRTIO_SCSI_T_TMF_I_T_NEXUS_RESET: target = req->req.tmf.lun[1]; s->resetting++; - QTAILQ_FOREACH(kid, &s->bus.qbus.children, sibling) { + + rcu_read_lock(); + QTAILQ_FOREACH_RCU(kid, &s->bus.qbus.children, sibling) { d = SCSI_DEVICE(kid->child); if (d->channel == 0 && d->id == target) { qdev_reset_all(&d->qdev); } } + rcu_read_unlock(); + s->resetting--; break; diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h index 14d476c587..2c6307e3ed 100644 --- a/include/hw/qdev-core.h +++ b/include/hw/qdev-core.h @@ -3,6 +3,8 @@ #include "qemu/queue.h" #include "qemu/bitmap.h" +#include "qemu/rcu.h" +#include "qemu/rcu_queue.h" #include "qom/object.h" #include "hw/hotplug.h" #include "hw/resettable.h" @@ -238,6 +240,7 @@ struct BusClass { }; typedef struct BusChild { + struct rcu_head rcu; DeviceState *child; int index; QTAILQ_ENTRY(BusChild) sibling; @@ -258,6 +261,12 @@ struct BusState { int max_index; bool realized; int num_children; + + /* + * children is a RCU QTAILQ, thus readers must use RCU to access it, + * and writers must hold the big qemu lock + */ + QTAILQ_HEAD(, BusChild) children; QLIST_ENTRY(BusState) sibling; ResettableState reset; diff --git a/tests/qtest/drive_del-test.c b/tests/qtest/drive_del-test.c index 2d765865ce..05184124a2 100644 --- a/tests/qtest/drive_del-test.c +++ b/tests/qtest/drive_del-test.c @@ -15,9 +15,6 @@ #include "libqos/virtio.h" #include "qapi/qmp/qdict.h" -/* TODO actually test the results and get rid of this */ -#define qmp_discard_response(q, ...) qobject_unref(qtest_qmp(q, __VA_ARGS__)) - static void drive_add(QTestState *qts) { char *resp = qtest_hmp(qts, "drive_add 0 if=none,id=drive0"); @@ -38,12 +35,11 @@ static void device_del(QTestState *qts) { QDict *response; - /* Complication: ignore DEVICE_DELETED event */ - qmp_discard_response(qts, "{'execute': 'device_del'," - " 'arguments': { 'id': 'dev0' } }"); - response = qtest_qmp_receive(qts); + response = qtest_qmp(qts, "{'execute': 'device_del'," + " 'arguments': { 'id': 'dev0' } }"); g_assert(response); g_assert(qdict_haskey(response, "return")); + qtest_qmp_eventwait(qts, "DEVICE_DELETED"); qobject_unref(response); }