From patchwork Thu Apr 16 20:36:22 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Maxim Levitsky X-Patchwork-Id: 1271901 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=OgjBV05Y; dkim-atps=neutral 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 ozlabs.org (Postfix) with ESMTPS id 4939xs44xKz9sP7 for ; Fri, 17 Apr 2020 06:37:05 +1000 (AEST) Received: from localhost ([::1]:39076 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jPBFv-00086L-Gx for incoming@patchwork.ozlabs.org; Thu, 16 Apr 2020 16:37:03 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60501) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jPBFZ-000838-J9 for qemu-devel@nongnu.org; Thu, 16 Apr 2020 16:36:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jPBFX-00043K-T0 for qemu-devel@nongnu.org; Thu, 16 Apr 2020 16:36:41 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:55970 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jPBFX-00042v-PY for qemu-devel@nongnu.org; Thu, 16 Apr 2020 16:36:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587069399; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=oMa/5d3tGunme1aUOe1TbXlozhP9DjIscaSAWG74tqw=; b=OgjBV05YxsxohNOb/IgI4Q/OlZNwz12mnnPQJqPxChcRa7rYuCWKNmqiB7coAfuCAIiXPI h0nF21PTpuM4PzhOWRuyHqEHoCH//tLMbgXLWNA8ftJ8hnx9B5/Q2NGW5C2BThIrvezXcr ZJ2wNN5AIXKFEYjFWierL8lYvgyzONM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-220-Ho9U53NXNYqTsfC2X5ZzFA-1; Thu, 16 Apr 2020 16:36:37 -0400 X-MC-Unique: Ho9U53NXNYqTsfC2X5ZzFA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 32CEC8010F1; Thu, 16 Apr 2020 20:36:36 +0000 (UTC) Received: from maximlenovopc.usersys.redhat.com (unknown [10.35.206.56]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4EFB5A099C; Thu, 16 Apr 2020 20:36:34 +0000 (UTC) From: Maxim Levitsky To: qemu-devel@nongnu.org Subject: [PATCH 2/4] device-core: use RCU for list of childs of a bus Date: Thu, 16 Apr 2020 23:36:22 +0300 Message-Id: <20200416203624.32366-3-mlevitsk@redhat.com> In-Reply-To: <20200416203624.32366-1-mlevitsk@redhat.com> References: <20200416203624.32366-1-mlevitsk@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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: Fam Zheng , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= , Eduardo Habkost , "Michael S. Tsirkin" , Maxim Levitsky , Paolo Bonzini Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" 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 --- hw/core/bus.c | 43 ++++++++++++++++++++----------- hw/core/qdev.c | 46 +++++++++++++++++++++++----------- hw/scsi/scsi-bus.c | 17 ++++++++++--- hw/scsi/virtio-scsi.c | 6 ++++- include/hw/qdev-core.h | 3 +++ include/hw/virtio/virtio-bus.h | 7 ++++-- 6 files changed, 87 insertions(+), 35 deletions(-) diff --git a/hw/core/bus.c b/hw/core/bus.c index 3dc0a825f0..cb7756ded1 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; + } } } @@ -90,9 +92,13 @@ static void bus_reset_child_foreach(Object *obj, ResettableChildCallback cb, BusState *bus = BUS(obj); BusChild *kid; - QTAILQ_FOREACH(kid, &bus->children, sibling) { + rcu_read_lock(); + + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { cb(OBJECT(kid->child), opaque, type); } + + rcu_read_unlock(); } static void qbus_realize(BusState *bus, DeviceState *parent, const char *name) @@ -138,10 +144,15 @@ static void bus_unparent(Object *obj) /* Only the main system bus has no parent, and that bus is never freed */ assert(bus->parent); - while ((kid = QTAILQ_FIRST(&bus->children)) != NULL) { + rcu_read_lock(); + + while ((kid = QTAILQ_FIRST_RCU(&bus->children)) != NULL) { DeviceState *dev = kid->child; object_unparent(OBJECT(dev)); } + + rcu_read_unlock(); + QLIST_REMOVE(bus, sibling); bus->parent->num_child_bus--; bus->parent = NULL; @@ -185,14 +196,18 @@ 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; - object_property_set_bool(OBJECT(dev), false, "realized", - &local_err); - if (local_err != NULL) { - break; + + WITH_RCU_READ_LOCK_GUARD(){ + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { + DeviceState *dev = kid->child; + object_property_set_bool(OBJECT(dev), false, "realized", + &local_err); + if (local_err != NULL) { + break; + } } } + if (bc->unrealize && local_err == NULL) { bc->unrealize(bus, &local_err); } diff --git a/hw/core/qdev.c b/hw/core/qdev.c index 85f062def7..f0c87e582e 100644 --- a/hw/core/qdev.c +++ b/hw/core/qdev.c @@ -50,26 +50,37 @@ 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; - QTAILQ_FOREACH(kid, &bus->children, sibling) { + rcu_read_lock(); + + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { if (kid->child == 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, NULL); - 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; } } + + rcu_read_unlock(); } static void bus_add_child(BusState *bus, DeviceState *child) @@ -82,7 +93,9 @@ static void bus_add_child(BusState *bus, DeviceState *child) kid->child = child; object_ref(OBJECT(kid->child)); - QTAILQ_INSERT_HEAD(&bus->children, kid, sibling); + rcu_read_lock(); + QTAILQ_INSERT_HEAD_RCU(&bus->children, kid, sibling); + rcu_read_unlock(); /* This transfers ownership of kid->child to the property. */ snprintf(name, sizeof(name), "child[%d]", kid->index); @@ -681,20 +694,23 @@ 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; + } } } } + return NULL; } diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c index 7bbc37acec..2bf6d005f3 100644 --- a/hw/scsi/scsi-bus.c +++ b/hw/scsi/scsi-bus.c @@ -412,7 +412,10 @@ 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(); + + QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) { DeviceState *qdev = kid->child; SCSIDevice *dev = SCSI_DEVICE(qdev); @@ -433,7 +436,7 @@ 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); @@ -442,6 +445,9 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r) i += 8; } } + + rcu_read_unlock(); + assert(i == n + 8); r->len = len; return true; @@ -1584,12 +1590,15 @@ 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(); + + QTAILQ_FOREACH_RCU(kid, &bus->qbus.children, sibling) { DeviceState *qdev = kid->child; SCSIDevice *dev = SCSI_DEVICE(qdev); if (dev->channel == channel && dev->id == id) { if (dev->lun == lun) { + rcu_read_unlock(); return dev; } @@ -1603,6 +1612,8 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun) } } } + + rcu_read_unlock(); return target_dev; } diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c index 472bbd233b..b0f4a35f81 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 1405b8a990..196253978b 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" @@ -218,6 +220,7 @@ struct BusClass { }; typedef struct BusChild { + struct rcu_head rcu; DeviceState *child; int index; QTAILQ_ENTRY(BusChild) sibling; diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h index 38c9399cd4..58733f28e2 100644 --- a/include/hw/virtio/virtio-bus.h +++ b/include/hw/virtio/virtio-bus.h @@ -128,8 +128,11 @@ void virtio_bus_set_vdev_config(VirtioBusState *bus, uint8_t *config); static inline VirtIODevice *virtio_bus_get_device(VirtioBusState *bus) { BusState *qbus = &bus->parent_obj; - BusChild *kid = QTAILQ_FIRST(&qbus->children); - DeviceState *qdev = kid ? kid->child : NULL; + BusChild *kid; + DeviceState *qdev; + + kid = QTAILQ_FIRST(&qbus->children); + qdev = kid ? kid->child : NULL; /* This is used on the data path, the cast is guaranteed * to succeed by the qdev machinery.