From patchwork Thu Jun 9 14:37:26 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Emanuele Giuseppe Esposito X-Patchwork-Id: 12875751 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 2A1F8C43334 for ; Thu, 9 Jun 2022 15:13:22 +0000 (UTC) Received: from localhost ([::1]:59382 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nzJqb-0000yY-3a for qemu-devel@archiver.kernel.org; Thu, 09 Jun 2022 11:13:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36362) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nzJI6-0002Nb-2l for qemu-devel@nongnu.org; Thu, 09 Jun 2022 10:37:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:35492) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nzJI2-00071x-Lb for qemu-devel@nongnu.org; Thu, 09 Jun 2022 10:37:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1654785457; 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=c1UwygJ8YnIPm+pDdNgiVSqRTl6Qaq4CDead5RjXiU0=; b=b+NkeJV3odDTY3h3yf9fVyqXUHiyt3vFYzUEtvn+UFAxkjRwNM+fpUP3hypFgX4vgU6HZK RMh9luQZZwRrNI2e8uhaWdYjNDiVoywLxoauqvEb9eFP0raUK3ckhjpJI7n6rpcQ1rTpzB MHFrZoxsZmvxBvkzAHNeMqvnvQRmaMw= 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-295-7LFewbqIMcy8gySz9NqqwQ-1; Thu, 09 Jun 2022 10:37:34 -0400 X-MC-Unique: 7LFewbqIMcy8gySz9NqqwQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 41E4B800971; Thu, 9 Jun 2022 14:37:34 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 02668492C3B; Thu, 9 Jun 2022 14:37:33 +0000 (UTC) From: Emanuele Giuseppe Esposito To: qemu-block@nongnu.org Cc: Kevin Wolf , Hanna Reitz , Stefan Hajnoczi , "Michael S. Tsirkin" , Paolo Bonzini , Fam Zheng , qemu-devel@nongnu.org, Emanuele Giuseppe Esposito Subject: [PATCH 7/8] VirtIOBlock: protect rq with its own lock Date: Thu, 9 Jun 2022 10:37:26 -0400 Message-Id: <20220609143727.1151816-8-eesposit@redhat.com> In-Reply-To: <20220609143727.1151816-1-eesposit@redhat.com> References: <20220609143727.1151816-1-eesposit@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 Received-SPF: pass client-ip=170.10.129.124; envelope-from=eesposit@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=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable 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" s->rq is pointing to the the VirtIOBlockReq list, and this list is read/written in: virtio_blk_reset = main loop, but caller calls ->stop_ioeventfd() and drains, so no iothread runs in parallel virtio_blk_save_device = main loop, but VM is stopped (migration), so iothread has no work on request list virtio_blk_load_device = same as save_device virtio_blk_device_realize = iothread is not created yet virtio_blk_handle_rw_error = io, here is why we need synchronization. s is device state and is shared accross all queues. Right now there is no problem, because iothread and main loop never access it at the same time, but if we introduce 1 iothread -> n virtqueue and 1 virtqueue -> 1 iothread mapping we might have two iothreads accessing the list at the same time virtio_blk_process_queued_requests: io, same problem as above. Therefore we need a virtio-blk to protect s->rq list. Signed-off-by: Emanuele Giuseppe Esposito Reviewed-by: Stefan Hajnoczi --- hw/block/virtio-blk.c | 38 ++++++++++++++++++++++++++-------- include/hw/virtio/virtio-blk.h | 5 ++++- 2 files changed, 33 insertions(+), 10 deletions(-) diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c index e1aaa606ba..88c61457e1 100644 --- a/hw/block/virtio-blk.c +++ b/hw/block/virtio-blk.c @@ -109,8 +109,10 @@ static int virtio_blk_handle_rw_error(VirtIOBlockReq *req, int error, /* Break the link as the next request is going to be parsed from the * ring again. Otherwise we may end up doing a double completion! */ req->mr_next = NULL; - req->next = s->rq; - s->rq = req; + WITH_QEMU_LOCK_GUARD(&s->req_mutex) { + req->next = s->rq; + s->rq = req; + } } else if (action == BLOCK_ERROR_ACTION_REPORT) { virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR); if (acct_failed) { @@ -860,10 +862,16 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq) void virtio_blk_process_queued_requests(VirtIOBlock *s, bool is_bh) { - VirtIOBlockReq *req = s->rq; + VirtIOBlockReq *req; MultiReqBuffer mrb = {}; - s->rq = NULL; + IO_CODE(); + + /* Detach queue from s->rq and process everything here */ + WITH_QEMU_LOCK_GUARD(&s->req_mutex) { + req = s->rq; + s->rq = NULL; + } aio_context_acquire(blk_get_aio_context(s->conf.conf.blk)); while (req) { @@ -896,6 +904,7 @@ void virtio_blk_restart_bh(void *opaque) { VirtIOBlock *s = opaque; + IO_CODE(); qemu_bh_delete(s->bh); s->bh = NULL; @@ -946,17 +955,20 @@ static void virtio_blk_reset(VirtIODevice *vdev) * stops all Iothreads. */ blk_drain(s->blk); + aio_context_release(ctx); /* We drop queued requests after blk_drain() because blk_drain() itself can * produce them. */ + qemu_mutex_lock(&s->req_mutex); while (s->rq) { req = s->rq; s->rq = req->next; + qemu_mutex_unlock(&s->req_mutex); virtqueue_detach_element(req->vq, &req->elem, 0); virtio_blk_free_request(req); + qemu_mutex_lock(&s->req_mutex); } - - aio_context_release(ctx); + qemu_mutex_unlock(&s->req_mutex); assert(!s->dataplane_started); blk_set_enable_write_cache(s->blk, s->original_wce); @@ -1120,10 +1132,14 @@ static void virtio_blk_set_status(VirtIODevice *vdev, uint8_t status) static void virtio_blk_save_device(VirtIODevice *vdev, QEMUFile *f) { VirtIOBlock *s = VIRTIO_BLK(vdev); - VirtIOBlockReq *req = s->rq; + VirtIOBlockReq *req; GLOBAL_STATE_CODE(); + WITH_QEMU_LOCK_GUARD(&s->req_mutex) { + req = s->rq; + } + while (req) { qemu_put_sbyte(f, 1); @@ -1165,8 +1181,10 @@ static int virtio_blk_load_device(VirtIODevice *vdev, QEMUFile *f, req = qemu_get_virtqueue_element(vdev, f, sizeof(VirtIOBlockReq)); virtio_blk_init_request(s, virtio_get_queue(vdev, vq_idx), req); - req->next = s->rq; - s->rq = req; + WITH_QEMU_LOCK_GUARD(&s->req_mutex) { + req->next = s->rq; + s->rq = req; + } } return 0; @@ -1272,6 +1290,7 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp) virtio_init(vdev, VIRTIO_ID_BLOCK, s->config_size); + qemu_mutex_init(&s->req_mutex); s->blk = conf->conf.blk; s->rq = NULL; s->sector_mask = (s->conf.conf.logical_block_size / BDRV_SECTOR_SIZE) - 1; @@ -1318,6 +1337,7 @@ static void virtio_blk_device_unrealize(DeviceState *dev) qemu_coroutine_dec_pool_size(conf->num_queues * conf->queue_size / 2); qemu_del_vm_change_state_handler(s->change); blockdev_mark_auto_del(s->blk); + qemu_mutex_destroy(&s->req_mutex); virtio_cleanup(vdev); } diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h index c334353b5a..5cb59994a8 100644 --- a/include/hw/virtio/virtio-blk.h +++ b/include/hw/virtio/virtio-blk.h @@ -53,7 +53,6 @@ struct VirtIOBlockReq; struct VirtIOBlock { VirtIODevice parent_obj; BlockBackend *blk; - void *rq; QEMUBH *bh; VirtIOBlkConf conf; unsigned short sector_mask; @@ -64,6 +63,10 @@ struct VirtIOBlock { struct VirtIOBlockDataPlane *dataplane; uint64_t host_features; size_t config_size; + + /* While the VM is running, req_mutex protects rq. */ + QemuMutex req_mutex; + struct VirtIOBlockReq *rq; }; typedef struct VirtIOBlockReq {