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bh=Xk8h587uLub3WTTQL8vL43Buo+pux0l49eabb4swi6I=; b=eSF5tahqNHDnzPFCGXo8t0DqvePFYQaSR7n9l72+5hvPk3ibgnW6Z+KCRZ34XnVAxZmHIS Ms+DkgMHiUXJ8ctq9m7YEg0kOcSLKOZrjcVTWSal81+n707rbTdfPL/LnH+zUdNgJeBKmL MN2sFgZZlRhoGXaIiBPYwIT9LzgfgeA= 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-460-F5wo2KNZNb6_B376m673gg-1; Wed, 30 Sep 2020 10:32:11 -0400 X-MC-Unique: F5wo2KNZNb6_B376m673gg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D39A5186840F for ; Wed, 30 Sep 2020 14:32:10 +0000 (UTC) Received: from starship (unknown [10.35.206.29]) by smtp.corp.redhat.com (Postfix) with ESMTP id B3F2A5576C; Wed, 30 Sep 2020 14:32:06 +0000 (UTC) Message-ID: Subject: Re: [PATCH 07/10] scsi/scsi-bus: scsi_device_find: don't return unrealized devices From: Maxim Levitsky To: Paolo Bonzini , qemu-devel@nongnu.org Date: Wed, 30 Sep 2020 17:32:05 +0300 In-Reply-To: <20200925172604.2142227-8-pbonzini@redhat.com> References: <20200925172604.2142227-1-pbonzini@redhat.com> <20200925172604.2142227-8-pbonzini@redhat.com> User-Agent: Evolution 3.36.3 (3.36.3-1.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=mlevitsk@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/30 00:31:59 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.469, 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_H5=0.001, RCVD_IN_MSPIKE_WL=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: stefanha@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 2020-09-25 at 13:26 -0400, Paolo Bonzini wrote: > From: Maxim Levitsky > > The device core first places a device on the bus and then realizes it. > Make scsi_device_find avoid returing such devices to avoid > races in drivers that use an iothread (currently virtio-scsi) > > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1812399 > > Suggested-by: Paolo Bonzini > Signed-off-by: Maxim Levitsky > Reviewed-by: Stefan Hajnoczi > Message-Id: <20200913160259.32145-7-mlevitsk@redhat.com> > Signed-off-by: Paolo Bonzini > --- > hw/scsi/scsi-bus.c | 83 +++++++++++++++++++++++++++++----------------- > 1 file changed, 53 insertions(+), 30 deletions(-) > > diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c > index 4ab9811cd8..7599113efe 100644 > --- a/hw/scsi/scsi-bus.c > +++ b/hw/scsi/scsi-bus.c > @@ -24,6 +24,55 @@ static void scsi_target_free_buf(SCSIRequest *req); > > static int next_scsi_bus; > > +static SCSIDevice *do_scsi_device_find(SCSIBus *bus, > + int channel, int id, int lun, > + bool include_unrealized) > +{ > + BusChild *kid; > + SCSIDevice *retval = NULL; > + > + 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) { > + retval = dev; > + break; Indeed, here no need to use goto, I probably removed some code that needed it before or just forgot about. > + } > + > + /* > + * If we don't find exact match (channel/bus/lun), > + * we will return the first device which matches channel/bus > + */ > + > + if (!retval) { > + retval = dev; > + } > + } > + } > + > + /* > + * This function might run on the IO thread and we might race against > + * main thread hot-plugging the device. > + * We assume that as soon as .realized is set to true we can let > + * the user access the device. > + */ > + > + if (retval && !include_unrealized && > + !qatomic_load_acquire(&retval->qdev.realized)) { > + retval = NULL; > + } > + > + return retval; > +} I guess you dropped the RCU locking here since you want the callers of this function to do it. I think it makes lot of sense. > + > +SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun) > +{ > + RCU_READ_LOCK_GUARD(); > + return do_scsi_device_find(bus, channel, id, lun, false); > +} > + > static void scsi_device_realize(SCSIDevice *s, Error **errp) > { > SCSIDeviceClass *sc = SCSI_DEVICE_GET_CLASS(s); > @@ -137,7 +186,10 @@ static bool scsi_bus_is_address_free(SCSIBus *bus, > int channel, int target, int lun, > SCSIDevice **p_dev) > { > - SCSIDevice *d = scsi_device_find(bus, channel, target, lun); > + SCSIDevice *d; > + > + RCU_READ_LOCK_GUARD(); > + d = do_scsi_device_find(bus, channel, target, lun, true); > if (d && d->lun == lun) { > if (p_dev) { > *p_dev = d; > @@ -1570,35 +1622,6 @@ static char *scsibus_get_fw_dev_path(DeviceState *dev) > qdev_fw_name(dev), d->id, d->lun); > } > > -SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun) > -{ > - BusChild *kid; > - SCSIDevice *target_dev = NULL; > - > - RCU_READ_LOCK_GUARD(); > - 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) { > - return dev; > - } > - > - /* > - * If we don't find exact match (channel/bus/lun), > - * we will return the first device which matches channel/bus > - */ > - > - if (!target_dev) { > - target_dev = dev; > - } > - } > - } > - > - return target_dev; > -} > - > /* SCSI request list. For simplicity, pv points to the whole device */ > > static int put_scsi_requests(QEMUFile *f, void *pv, size_t size, Best regards, Maxim Levitsky