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Mon, 31 Aug 2020 11:01:51 -0400 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-307-HkyID_c7OKe-Hz_xEX3a0g-1; Mon, 31 Aug 2020 11:01:45 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E178210ABDA0; Mon, 31 Aug 2020 15:01:44 +0000 (UTC) Received: from localhost.localdomain (unknown [10.35.206.190]) by smtp.corp.redhat.com (Postfix) with ESMTP id 93ECF19C4F; Mon, 31 Aug 2020 15:01:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1598886107; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=FZYL7a+wM3VyXEfeS23vdxhnPrcCvz6aLxgaGhEQPJ4=; b=GruEH7Q2Hd/+fwOw6QNc776Yv49SVmNg/6novRI3+/5hEBX/6TrHOO1nkVMyGV+vejmsPy UaVKeChBq163R+HJPklGm4Fc31itN7aoNZVgGV2kv0hyj8/A1sbsSIIH3RP6+9pQVXhN/p PmMezIcm8fJE7WqnXLWtidy/KLcuwCI= X-MC-Unique: HkyID_c7OKe-Hz_xEX3a0g-1 From: Maxim Levitsky To: qemu-devel@nongnu.org Subject: [PATCH v4 4/9] device-core: use RCU for list of childs of a bus Date: Mon, 31 Aug 2020 18:01:19 +0300 Message-Id: <20200831150124.206267-5-mlevitsk@redhat.com> In-Reply-To: <20200831150124.206267-1-mlevitsk@redhat.com> References: <20200831150124.206267-1-mlevitsk@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; 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 = 2020/08/31 10:30:34 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_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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: Fam Zheng , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , Eduardo Habkost , "Michael S. Tsirkin" , Maxim Levitsky , Stefan Hajnoczi , Paolo Bonzini Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" 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 --- hw/core/bus.c | 28 ++++++++++++++++++---------- hw/core/qdev.c | 37 +++++++++++++++++++++++-------------- hw/scsi/scsi-bus.c | 17 ++++++++++++++--- hw/scsi/virtio-scsi.c | 6 +++++- include/hw/qdev-core.h | 9 +++++++++ 5 files changed, 69 insertions(+), 28 deletions(-) diff --git a/hw/core/bus.c b/hw/core/bus.c index 6b987b6946..385eb3ad5a 100644 --- a/hw/core/bus.c +++ b/hw/core/bus.c @@ -49,12 +49,14 @@ int qbus_walk_children(BusState *bus, } } =20 - QTAILQ_FOREACH(kid, &bus->children, sibling) { - err =3D 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 =3D qdev_walk_children(kid->child, + pre_devfn, pre_busfn, + post_devfn, post_busfn, opaque); + if (err < 0) { + return err; + } } } =20 @@ -90,9 +92,13 @@ static void bus_reset_child_foreach(Object *obj, Resetta= bleChildCallback cb, BusState *bus =3D BUS(obj); BusChild *kid; =20 - 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(); } =20 static void qbus_init(BusState *bus, DeviceState *parent, const char *name) @@ -194,9 +200,11 @@ static void bus_set_realized(Object *obj, bool value, = Error **errp) =20 /* TODO: recursive realization */ } else if (!value && bus->realized) { - QTAILQ_FOREACH(kid, &bus->children, sibling) { - DeviceState *dev =3D kid->child; - qdev_unrealize(dev); + WITH_RCU_READ_LOCK_GUARD() { + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { + DeviceState *dev =3D kid->child; + qdev_unrealize(dev); + } } if (bc->unrealize) { bc->unrealize(bus); diff --git a/hw/core/qdev.c b/hw/core/qdev.c index 96772a15bd..28e5fff5ed 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; } =20 +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]; =20 snprintf(name, sizeof(name), "child[%d]", kid->index); - QTAILQ_REMOVE(&bus->children, kid, sibling); + QTAILQ_REMOVE_RCU(&bus->children, kid, sibling); =20 bus->num_children--; =20 /* 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 *chi= ld) kid->child =3D child; object_ref(OBJECT(kid->child)); =20 - QTAILQ_INSERT_HEAD(&bus->children, kid, sibling); + QTAILQ_INSERT_HEAD_RCU(&bus->children, kid, sibling); =20 /* This transfers ownership of kid->child to the property. */ snprintf(name, sizeof(name), "child[%d]", kid->index); @@ -659,17 +666,19 @@ DeviceState *qdev_find_recursive(BusState *bus, const= char *id) DeviceState *ret; BusState *child; =20 - QTAILQ_FOREACH(kid, &bus->children, sibling) { - DeviceState *dev =3D kid->child; + WITH_RCU_READ_LOCK_GUARD() { + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { + DeviceState *dev =3D kid->child; =20 - if (dev->id && strcmp(dev->id, id) =3D=3D 0) { - return dev; - } + if (dev->id && strcmp(dev->id, id) =3D=3D 0) { + return dev; + } =20 - QLIST_FOREACH(child, &dev->child_bus, sibling) { - ret =3D qdev_find_recursive(child, id); - if (ret) { - return ret; + QLIST_FOREACH(child, &dev->child_bus, sibling) { + ret =3D qdev_find_recursive(child, id); + if (ret) { + return ret; + } } } } diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c index f8adfbc2a5..92d412b65c 100644 --- a/hw/scsi/scsi-bus.c +++ b/hw/scsi/scsi-bus.c @@ -400,7 +400,10 @@ static bool scsi_target_emulate_report_luns(SCSITarget= Req *r) id =3D r->req.dev->id; found_lun0 =3D false; n =3D 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 =3D kid->child; SCSIDevice *dev =3D SCSI_DEVICE(qdev); =20 @@ -421,7 +424,7 @@ static bool scsi_target_emulate_report_luns(SCSITargetR= eq *r) memset(r->buf, 0, len); stl_be_p(&r->buf[0], n); i =3D 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 =3D kid->child; SCSIDevice *dev =3D SCSI_DEVICE(qdev); =20 @@ -430,6 +433,9 @@ static bool scsi_target_emulate_report_luns(SCSITargetR= eq *r) i +=3D 8; } } + + rcu_read_unlock(); + assert(i =3D=3D n + 8); r->len =3D len; return true; @@ -1572,12 +1578,15 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int chan= nel, int id, int lun) BusChild *kid; SCSIDevice *target_dev =3D NULL; =20 - QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) { + rcu_read_lock(); + + QTAILQ_FOREACH_RCU(kid, &bus->qbus.children, sibling) { DeviceState *qdev =3D kid->child; SCSIDevice *dev =3D SCSI_DEVICE(qdev); =20 if (dev->channel =3D=3D channel && dev->id =3D=3D id) { if (dev->lun =3D=3D lun) { + rcu_read_unlock(); return dev; } =20 @@ -1591,6 +1600,8 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int channe= l, int id, int lun) } } } + + rcu_read_unlock(); return target_dev; } =20 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, VirtIOSC= SIReq *req) case VIRTIO_SCSI_T_TMF_I_T_NEXUS_RESET: target =3D 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 =3D SCSI_DEVICE(kid->child); if (d->channel =3D=3D 0 && d->id =3D=3D target) { qdev_reset_all(&d->qdev); } } + rcu_read_unlock(); + s->resetting--; break; =20 diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h index ea3f73a282..7c7728ff86 100644 --- a/include/hw/qdev-core.h +++ b/include/hw/qdev-core.h @@ -3,6 +3,8 @@ =20 #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 { }; =20 typedef struct BusChild { + struct rcu_head rcu; DeviceState *child; int index; QTAILQ_ENTRY(BusChild) sibling; @@ -250,6 +253,12 @@ 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; --=20 2.26.2