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Tsirkin" , Kevin Wolf , Hanna Reitz , Sergio Lopez , Emanuele Giuseppe Esposito Subject: [PATCH] virtio-blk: simplify virtio_blk_dma_restart_cb() Date: Wed, 2 Nov 2022 14:23:37 -0400 Message-Id: <20221102182337.252202-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 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=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.048, 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: , Sender: "Qemu-devel" Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1667413463097100003 Content-Type: text/plain; charset="utf-8" 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 --- 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; =20 void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq); -void virtio_blk_process_queued_requests(VirtIOBlock *s, bool is_bh); =20 #endif diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-bl= k.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; } =20 - /* 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 =3D 0; i < nvqs; i++) { VirtQueue *vq =3D 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 =3D true; s->starting =3D false; vblk->dataplane_started =3D 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); =20 - /* Drain and try to switch bs back to the QEMU main loop. If other use= rs - * 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); =20 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 *vde= v, VirtQueue *vq) virtio_blk_handle_vq(s, vq); } =20 -void virtio_blk_process_queued_requests(VirtIOBlock *s, bool is_bh) +static void virtio_blk_dma_restart_bh(void *opaque) { + VirtIOBlock *s =3D opaque; + VirtIOBlockReq *req =3D s->rq; MultiReqBuffer mrb =3D {}; =20 @@ -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)); } =20 -static void virtio_blk_dma_restart_bh(void *opaque) -{ - VirtIOBlock *s =3D opaque; - - qemu_bh_delete(s->bh); - s->bh =3D NULL; - - virtio_blk_process_queued_requests(s, true); -} - static void virtio_blk_dma_restart_cb(void *opaque, bool running, RunState state) { VirtIOBlock *s =3D opaque; - BusState *qbus =3D BUS(qdev_get_parent_bus(DEVICE(s))); - VirtioBusState *bus =3D VIRTIO_BUS(qbus); =20 if (!running) { return; } =20 - /* - * 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 =3D 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); } =20 static void virtio_blk_reset(VirtIODevice *vdev) @@ -1213,7 +1199,13 @@ static void virtio_blk_device_realize(DeviceState *d= ev, Error **errp) return; } =20 - s->change =3D 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 =3D + 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); =20 --=20 2.38.1