From patchwork Thu Nov 23 19:49:28 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 13466750 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org 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 smtp.lore.kernel.org (Postfix) with ESMTPS id B9659C5AD4C for ; Thu, 23 Nov 2023 19:50:32 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1r6Fhn-00023e-Kv; Thu, 23 Nov 2023 14:49:43 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r6Fhm-0001zc-3a for qemu-devel@nongnu.org; Thu, 23 Nov 2023 14:49:42 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r6Fhk-0000d4-7Y for qemu-devel@nongnu.org; Thu, 23 Nov 2023 14:49:41 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1700768979; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=q7quI/mL9SJ1gDnH5dssu/KWo/kzn2Ys+Riu7XflH/I=; b=h9zpq5kvKxB2Mua+7Cko5d5oTBUFwtAHlQ14Oka48QSfyuZlvnbmg84ZkwHHSVJG+HA44E 13UZNhoRs1BOOSY7vr2jXJkTm9mnbeCBMLXv/CloYczcWwkdVye2s1uZOAhAbZeSFXPslD IsTRxahY58Xn4Vblf7T6wAaWilaMAts= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-231-2bvx6RTOPyCwE79Uc3ea7A-1; Thu, 23 Nov 2023 14:49:37 -0500 X-MC-Unique: 2bvx6RTOPyCwE79Uc3ea7A-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 17E6829AA399; Thu, 23 Nov 2023 19:49:37 +0000 (UTC) Received: from localhost (unknown [10.39.192.72]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5365E2026D4C; Thu, 23 Nov 2023 19:49:36 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: "Michael S. Tsirkin" , David Hildenbrand , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Peter Xu , Paolo Bonzini , Fam Zheng , Stefan Hajnoczi Subject: [PATCH 1/4] scsi: only access SCSIDevice->requests from one thread Date: Thu, 23 Nov 2023 14:49:28 -0500 Message-ID: <20231123194931.171598-2-stefanha@redhat.com> In-Reply-To: <20231123194931.171598-1-stefanha@redhat.com> References: <20231123194931.171598-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.058, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Stop depending on the AioContext lock and instead access SCSIDevice->requests from only one thread at a time: - When the VM is running only the BlockBackend's AioContext may access the requests list. - When the VM is stopped only the main loop may access the requests list. These constraints protect the requests list without the need for locking in the I/O code path. Note that multiple IOThreads are not supported yet because the code assumes all SCSIRequests are executed from a single AioContext. Leave that as future work. Signed-off-by: Stefan Hajnoczi Reviewed-by: Eric Blake --- include/hw/scsi/scsi.h | 7 +- hw/scsi/scsi-bus.c | 174 ++++++++++++++++++++++++++++------------- 2 files changed, 124 insertions(+), 57 deletions(-) diff --git a/include/hw/scsi/scsi.h b/include/hw/scsi/scsi.h index 3692ca82f3..10c4e8288d 100644 --- a/include/hw/scsi/scsi.h +++ b/include/hw/scsi/scsi.h @@ -69,14 +69,19 @@ struct SCSIDevice { DeviceState qdev; VMChangeStateEntry *vmsentry; - QEMUBH *bh; uint32_t id; BlockConf conf; SCSISense unit_attention; bool sense_is_ua; uint8_t sense[SCSI_SENSE_BUF_SIZE]; uint32_t sense_len; + + /* + * The requests list is only accessed from the AioContext that executes + * requests or from the main loop when IOThread processing is stopped. + */ QTAILQ_HEAD(, SCSIRequest) requests; + uint32_t channel; uint32_t lun; int blocksize; diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c index fc4b77fdb0..b8bfde9565 100644 --- a/hw/scsi/scsi-bus.c +++ b/hw/scsi/scsi-bus.c @@ -85,6 +85,82 @@ SCSIDevice *scsi_device_get(SCSIBus *bus, int channel, int id, int lun) return d; } +/* + * Invoke @fn() for each enqueued request in device @s. Must be called from the + * main loop thread while the guest is stopped. This is only suitable for + * vmstate ->put(), use scsi_device_for_each_req_async() for other cases. + */ +static void scsi_device_for_each_req_sync(SCSIDevice *s, + void (*fn)(SCSIRequest *, void *), + void *opaque) +{ + SCSIRequest *req; + SCSIRequest *next_req; + + assert(!runstate_is_running()); + assert(qemu_in_main_thread()); + + QTAILQ_FOREACH_SAFE(req, &s->requests, next, next_req) { + fn(req, opaque); + } +} + +typedef struct { + SCSIDevice *s; + void (*fn)(SCSIRequest *, void *); + void *fn_opaque; +} SCSIDeviceForEachReqAsyncData; + +static void scsi_device_for_each_req_async_bh(void *opaque) +{ + g_autofree SCSIDeviceForEachReqAsyncData *data = opaque; + SCSIDevice *s = data->s; + SCSIRequest *req; + SCSIRequest *next; + + /* + * It is unlikely that the AioContext will change before this BH is called, + * but if it happens then ->requests must not be accessed from this + * AioContext. + */ + if (blk_get_aio_context(s->conf.blk) == qemu_get_current_aio_context()) { + QTAILQ_FOREACH_SAFE(req, &s->requests, next, next) { + data->fn(req, data->fn_opaque); + } + } + + /* Drop the reference taken by scsi_device_for_each_req_async() */ + object_unref(OBJECT(s)); +} + +/* + * Schedule @fn() to be invoked for each enqueued request in device @s. @fn() + * runs in the AioContext that is executing the request. + */ +static void scsi_device_for_each_req_async(SCSIDevice *s, + void (*fn)(SCSIRequest *, void *), + void *opaque) +{ + assert(qemu_in_main_thread()); + + SCSIDeviceForEachReqAsyncData *data = + g_new(SCSIDeviceForEachReqAsyncData, 1); + + data->s = s; + data->fn = fn; + data->fn_opaque = opaque; + + /* + * Hold a reference to the SCSIDevice until + * scsi_device_for_each_req_async_bh() finishes. + */ + object_ref(OBJECT(s)); + + aio_bh_schedule_oneshot(blk_get_aio_context(s->conf.blk), + scsi_device_for_each_req_async_bh, + data); +} + static void scsi_device_realize(SCSIDevice *s, Error **errp) { SCSIDeviceClass *sc = SCSI_DEVICE_GET_CLASS(s); @@ -144,20 +220,18 @@ void scsi_bus_init_named(SCSIBus *bus, size_t bus_size, DeviceState *host, qbus_set_bus_hotplug_handler(BUS(bus)); } -static void scsi_dma_restart_bh(void *opaque) +void scsi_req_retry(SCSIRequest *req) { - SCSIDevice *s = opaque; - SCSIRequest *req, *next; + req->retry = true; +} - qemu_bh_delete(s->bh); - s->bh = NULL; - - aio_context_acquire(blk_get_aio_context(s->conf.blk)); - QTAILQ_FOREACH_SAFE(req, &s->requests, next, next) { - scsi_req_ref(req); - if (req->retry) { - req->retry = false; - switch (req->cmd.mode) { +/* Called in the AioContext that is executing the request */ +static void scsi_dma_restart_req(SCSIRequest *req, void *opaque) +{ + scsi_req_ref(req); + if (req->retry) { + req->retry = false; + switch (req->cmd.mode) { case SCSI_XFER_FROM_DEV: case SCSI_XFER_TO_DEV: scsi_req_continue(req); @@ -166,37 +240,22 @@ static void scsi_dma_restart_bh(void *opaque) scsi_req_dequeue(req); scsi_req_enqueue(req); break; - } } - scsi_req_unref(req); } - aio_context_release(blk_get_aio_context(s->conf.blk)); - /* Drop the reference that was acquired in scsi_dma_restart_cb */ - object_unref(OBJECT(s)); -} - -void scsi_req_retry(SCSIRequest *req) -{ - /* No need to save a reference, because scsi_dma_restart_bh just - * looks at the request list. */ - req->retry = true; + scsi_req_unref(req); } static void scsi_dma_restart_cb(void *opaque, bool running, RunState state) { SCSIDevice *s = opaque; + assert(qemu_in_main_thread()); + if (!running) { return; } - if (!s->bh) { - AioContext *ctx = blk_get_aio_context(s->conf.blk); - /* The reference is dropped in scsi_dma_restart_bh.*/ - object_ref(OBJECT(s)); - s->bh = aio_bh_new_guarded(ctx, scsi_dma_restart_bh, s, - &DEVICE(s)->mem_reentrancy_guard); - qemu_bh_schedule(s->bh); - } + + scsi_device_for_each_req_async(s, scsi_dma_restart_req, NULL); } static bool scsi_bus_is_address_free(SCSIBus *bus, @@ -1657,15 +1716,16 @@ void scsi_device_set_ua(SCSIDevice *sdev, SCSISense sense) } } +static void scsi_device_purge_one_req(SCSIRequest *req, void *opaque) +{ + scsi_req_cancel_async(req, NULL); +} + void scsi_device_purge_requests(SCSIDevice *sdev, SCSISense sense) { - SCSIRequest *req; + scsi_device_for_each_req_async(sdev, scsi_device_purge_one_req, NULL); aio_context_acquire(blk_get_aio_context(sdev->conf.blk)); - while (!QTAILQ_EMPTY(&sdev->requests)) { - req = QTAILQ_FIRST(&sdev->requests); - scsi_req_cancel_async(req, NULL); - } blk_drain(sdev->conf.blk); aio_context_release(blk_get_aio_context(sdev->conf.blk)); scsi_device_set_ua(sdev, sense); @@ -1737,31 +1797,33 @@ static char *scsibus_get_fw_dev_path(DeviceState *dev) /* SCSI request list. For simplicity, pv points to the whole device */ +static void put_scsi_req(SCSIRequest *req, void *opaque) +{ + QEMUFile *f = opaque; + + assert(!req->io_canceled); + assert(req->status == -1 && req->host_status == -1); + assert(req->enqueued); + + qemu_put_sbyte(f, req->retry ? 1 : 2); + qemu_put_buffer(f, req->cmd.buf, sizeof(req->cmd.buf)); + qemu_put_be32s(f, &req->tag); + qemu_put_be32s(f, &req->lun); + if (req->bus->info->save_request) { + req->bus->info->save_request(f, req); + } + if (req->ops->save_request) { + req->ops->save_request(f, req); + } +} + static int put_scsi_requests(QEMUFile *f, void *pv, size_t size, const VMStateField *field, JSONWriter *vmdesc) { SCSIDevice *s = pv; - SCSIBus *bus = DO_UPCAST(SCSIBus, qbus, s->qdev.parent_bus); - SCSIRequest *req; - QTAILQ_FOREACH(req, &s->requests, next) { - assert(!req->io_canceled); - assert(req->status == -1 && req->host_status == -1); - assert(req->enqueued); - - qemu_put_sbyte(f, req->retry ? 1 : 2); - qemu_put_buffer(f, req->cmd.buf, sizeof(req->cmd.buf)); - qemu_put_be32s(f, &req->tag); - qemu_put_be32s(f, &req->lun); - if (bus->info->save_request) { - bus->info->save_request(f, req); - } - if (req->ops->save_request) { - req->ops->save_request(f, req); - } - } + scsi_device_for_each_req_sync(s, put_scsi_req, f); qemu_put_sbyte(f, 0); - return 0; }