From patchwork Mon May 11 16:09:47 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Maxim Levitsky X-Patchwork-Id: 11541265 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id ABC32912 for ; Mon, 11 May 2020 16:12:13 +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 82E3D2070B for ; Mon, 11 May 2020 16:12:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="fOvOAEvp" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 82E3D2070B 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+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:60604 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jYB2K-0005as-Lz for patchwork-qemu-devel@patchwork.kernel.org; Mon, 11 May 2020 12:12:12 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48246) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jYB0O-0002LY-St for qemu-devel@nongnu.org; Mon, 11 May 2020 12:10:12 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:57029 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jYB0N-00016m-N6 for qemu-devel@nongnu.org; Mon, 11 May 2020 12:10:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589213410; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:content-type:content-type:in-reply-to:in-reply-to: references:references; bh=3ML6lECeaqVQT5MGrBV/oBAq/3bu8IGqgGkuLlw17bo=; b=fOvOAEvpy4j9qiJKAYrMn8BOH0dPTnYISGfMKsMQmM+IMD+lANyjyXqZh7En8yLl3xHwGu yWnlLpg8HBwrxbv9viCUa9JI7MnARTLrhKc9U8cZBQSl4rrCbtmdL/tnCKQMcV0qi6120+ 90n51cbE9hGO2TcFvcYcBAKqp0JJpvQ= 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-61-2tHjkLXRNRqCVLei7fNW4g-1; Mon, 11 May 2020 12:10:09 -0400 X-MC-Unique: 2tHjkLXRNRqCVLei7fNW4g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1FF33107ACF3; Mon, 11 May 2020 16:10:08 +0000 (UTC) Received: from maximlenovopc.usersys.redhat.com (unknown [10.35.206.222]) by smtp.corp.redhat.com (Postfix) with ESMTP id 786AF5C1B5; Mon, 11 May 2020 16:10:02 +0000 (UTC) From: Maxim Levitsky To: qemu-devel@nongnu.org Subject: [PATCH v2 3/7] device-core: use RCU for list of childs of a bus Date: Mon, 11 May 2020 19:09:47 +0300 Message-Id: <20200511160951.8733-4-mlevitsk@redhat.com> In-Reply-To: <20200511160951.8733-1-mlevitsk@redhat.com> References: <20200511160951.8733-1-mlevitsk@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=207.211.31.120; envelope-from=mlevitsk@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/11 02:55:57 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: 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+patchwork-qemu-devel=patchwork.kernel.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 | 36 +++++++++++++++++++++++------------- hw/core/qdev.c | 37 +++++++++++++++++++++++-------------- hw/scsi/scsi-bus.c | 17 ++++++++++++++--- hw/scsi/virtio-scsi.c | 6 +++++- include/hw/qdev-core.h | 3 +++ 5 files changed, 68 insertions(+), 31 deletions(-) diff --git a/hw/core/bus.c b/hw/core/bus.c index 3dc0a825f0..dd6b155ff1 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) @@ -185,14 +191,18 @@ 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 dd77a56067..732789e2b7 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, 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; } } } @@ -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); @@ -682,17 +689,19 @@ 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 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 d87d989e72..ef47cb2d9c 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" @@ -230,6 +232,7 @@ struct BusClass { }; typedef struct BusChild { + struct rcu_head rcu; DeviceState *child; int index; QTAILQ_ENTRY(BusChild) sibling;