From mboxrd@z Thu Jan 1 00:00:00 1970 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 235BEC25B50 for ; Mon, 23 Jan 2023 20:05:26 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pK33a-0003sD-9X; Mon, 23 Jan 2023 15:04:42 -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 1pK33P-0003ns-5K for qemu-devel@nongnu.org; Mon, 23 Jan 2023 15:04:32 -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 1pK33M-0005ip-1c for qemu-devel@nongnu.org; Mon, 23 Jan 2023 15:04:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674504265; 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=a38ePrpO98d+EwnW67WNcaJdZ+64WIiOIuLVudDG1eI=; b=ELbrxuN4vGDwEGLSLz/Ar1DwRwPhWAUCscH+fdu779oHMau9NDXcks2MKWKge7DqW3V1jS 8Cu3vUaK6Rtg7ltvbxnvpstpNeTNQQYSmYHnC3DrLt7pVxiOtt8DIOinz7pRDKWW9dYWYd hOaS26yYop1iGubugeMvZ3i27hWri6M= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-453-GHs0CYxROK6GCHDy11MXMg-1; Mon, 23 Jan 2023 15:04:24 -0500 X-MC-Unique: GHs0CYxROK6GCHDy11MXMg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4707885C064; Mon, 23 Jan 2023 20:04:24 +0000 (UTC) Received: from localhost (unknown [10.39.193.206]) by smtp.corp.redhat.com (Postfix) with ESMTP id A04D9401530E; Mon, 23 Jan 2023 20:04:23 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Hanna Reitz , "Michael S. Tsirkin" , Kevin Wolf , Stefan Hajnoczi , Fam Zheng , qemu-block@nongnu.org, Paolo Bonzini , Sergio Lopez , Emanuele Giuseppe Esposito Subject: [PULL 2/3] virtio-blk: simplify virtio_blk_dma_restart_cb() Date: Mon, 23 Jan 2023 15:04:16 -0500 Message-Id: <20230123200417.169053-3-stefanha@redhat.com> In-Reply-To: <20230123200417.169053-1-stefanha@redhat.com> References: <20230123200417.169053-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 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: -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: 2.1.29 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 virtio_blk_dma_restart_cb() is tricky because the BH must deal with virtio_blk_data_plane_start()/virtio_blk_data_plane_stop() being called. There are two issues with the code: 1. virtio_blk_realize() should use qdev_add_vm_change_state_handler() instead of qemu_add_vm_change_state_handler(). This ensures the ordering with virtio_init()'s vm change state handler that calls virtio_blk_data_plane_start()/virtio_blk_data_plane_stop() is well-defined. Then blk's AioContext is guaranteed to be up-to-date in virtio_blk_dma_restart_cb() and it's no longer necessary to have a special case for virtio_blk_data_plane_start(). 2. Only blk_drain() waits for virtio_blk_dma_restart_cb()'s blk_inc_in_flight() to be decremented. The bdrv_drain() family of functions do not wait for BlockBackend's in_flight counter to reach zero. virtio_blk_data_plane_stop() relies on blk_set_aio_context()'s implicit drain, but that's a bdrv_drain() and not a blk_drain(). Note that virtio_blk_reset() already correctly relies on blk_drain(). If virtio_blk_data_plane_stop() switches to blk_drain() then we can properly wait for pending virtio_blk_dma_restart_bh() calls. Once these issues are taken care of the code becomes simpler. This change is in preparation for multiple IOThreads in virtio-blk where we need to clean up the multi-threading behavior. I ran the reproducer from commit 49b44549ace7 ("virtio-blk: On restart, process queued requests in the proper context") to check that there is no regression. Cc: Sergio Lopez Cc: Kevin Wolf Cc: Emanuele Giuseppe Esposito Signed-off-by: Stefan Hajnoczi Acked-by: Michael S. Tsirkin Reviewed-by: Emanuele Giuseppe Esposito Message-id: 20221102182337.252202-1-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi --- include/hw/virtio/virtio-blk.h | 2 -- hw/block/dataplane/virtio-blk.c | 17 +++++------- hw/block/virtio-blk.c | 46 ++++++++++++++------------------- 3 files changed, 26 insertions(+), 39 deletions(-) diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h index 7f589b4146..dafec432ce 100644 --- a/include/hw/virtio/virtio-blk.h +++ b/include/hw/virtio/virtio-blk.h @@ -55,7 +55,6 @@ struct VirtIOBlock { VirtIODevice parent_obj; BlockBackend *blk; void *rq; - QEMUBH *bh; VirtIOBlkConf conf; unsigned short sector_mask; bool original_wce; @@ -93,6 +92,5 @@ typedef struct MultiReqBuffer { } MultiReqBuffer; void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq); -void virtio_blk_process_queued_requests(VirtIOBlock *s, bool is_bh); #endif diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c index 26f965cabc..b28d81737e 100644 --- a/hw/block/dataplane/virtio-blk.c +++ b/hw/block/dataplane/virtio-blk.c @@ -237,9 +237,6 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev) goto fail_aio_context; } - /* Process queued requests before the ones in vring */ - virtio_blk_process_queued_requests(vblk, false); - /* Kick right away to begin processing requests already in vring */ for (i = 0; i < nvqs; i++) { VirtQueue *vq = virtio_get_queue(s->vdev, i); @@ -272,11 +269,6 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev) fail_host_notifiers: k->set_guest_notifiers(qbus->parent, nvqs, false); fail_guest_notifiers: - /* - * If we failed to set up the guest notifiers queued requests will be - * processed on the main context. - */ - virtio_blk_process_queued_requests(vblk, false); vblk->dataplane_disabled = true; s->starting = false; vblk->dataplane_started = true; @@ -325,8 +317,13 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev) aio_context_acquire(s->ctx); aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s); - /* Drain and try to switch bs back to the QEMU main loop. If other users - * keep the BlockBackend in the iothread, that's ok */ + /* Wait for virtio_blk_dma_restart_bh() and in flight I/O to complete */ + blk_drain(s->conf->conf.blk); + + /* + * Try to switch bs back to the QEMU main loop. If other users keep the + * BlockBackend in the iothread, that's ok + */ blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context(), NULL); aio_context_release(s->ctx); diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c index f717550fdc..1762517878 100644 --- a/hw/block/virtio-blk.c +++ b/hw/block/virtio-blk.c @@ -806,8 +806,10 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq) virtio_blk_handle_vq(s, vq); } -void virtio_blk_process_queued_requests(VirtIOBlock *s, bool is_bh) +static void virtio_blk_dma_restart_bh(void *opaque) { + VirtIOBlock *s = opaque; + VirtIOBlockReq *req = s->rq; MultiReqBuffer mrb = {}; @@ -834,43 +836,27 @@ void virtio_blk_process_queued_requests(VirtIOBlock *s, bool is_bh) if (mrb.num_reqs) { virtio_blk_submit_multireq(s, &mrb); } - if (is_bh) { - blk_dec_in_flight(s->conf.conf.blk); - } + + /* Paired with inc in virtio_blk_dma_restart_cb() */ + blk_dec_in_flight(s->conf.conf.blk); + aio_context_release(blk_get_aio_context(s->conf.conf.blk)); } -static void virtio_blk_dma_restart_bh(void *opaque) -{ - VirtIOBlock *s = opaque; - - qemu_bh_delete(s->bh); - s->bh = NULL; - - virtio_blk_process_queued_requests(s, true); -} - static void virtio_blk_dma_restart_cb(void *opaque, bool running, RunState state) { VirtIOBlock *s = opaque; - BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s))); - VirtioBusState *bus = VIRTIO_BUS(qbus); if (!running) { return; } - /* - * If ioeventfd is enabled, don't schedule the BH here as queued - * requests will be processed while starting the data plane. - */ - if (!s->bh && !virtio_bus_ioeventfd_enabled(bus)) { - s->bh = aio_bh_new(blk_get_aio_context(s->conf.conf.blk), - virtio_blk_dma_restart_bh, s); - blk_inc_in_flight(s->conf.conf.blk); - qemu_bh_schedule(s->bh); - } + /* Paired with dec in virtio_blk_dma_restart_bh() */ + blk_inc_in_flight(s->conf.conf.blk); + + aio_bh_schedule_oneshot(blk_get_aio_context(s->conf.conf.blk), + virtio_blk_dma_restart_bh, s); } static void virtio_blk_reset(VirtIODevice *vdev) @@ -1213,7 +1199,13 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp) return; } - s->change = qemu_add_vm_change_state_handler(virtio_blk_dma_restart_cb, s); + /* + * This must be after virtio_init() so virtio_blk_dma_restart_cb() gets + * called after ->start_ioeventfd() has already set blk's AioContext. + */ + s->change = + qdev_add_vm_change_state_handler(dev, virtio_blk_dma_restart_cb, s); + blk_ram_registrar_init(&s->blk_ram_registrar, s->blk); blk_set_dev_ops(s->blk, &virtio_block_ops, s); -- 2.39.0