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bh=n6KtD+qjUjkWlbaKcCQyIYdZ7FHRvWfBKaUiaTyFFfw=; b=X981iTN3oIBDXFTfRZ3/B8MQ39VHl7JSvsjo1WDFWVJwN0S3qEN1VqTn41dZHtN7wXwrnj ztW8Z2Rdt9KKllX0leypnmL7aFKbMIIgOdOaU6qAoFANYunu08Umi1LWb7vCv+q1v6sRWT n8wRi3p19LWxIaDf5W4nwskLHXNCT7w= X-MC-Unique: S7DftUEKNWmZU-iZX5SiLQ-1 From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org Subject: [PATCH for-8.2] export/vhost-user-blk: Fix consecutive drains Date: Fri, 24 Nov 2023 18:44:36 +0100 Message-ID: <20231124174436.46536-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 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=216.145.221.124; envelope-from=kwolf@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, 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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1700847939735100003 Content-Type: text/plain; charset="utf-8" The vhost-user-blk export implement AioContext switches in its drain implementation. This means that on drain_begin, it detaches the server from its AioContext and on drain_end, attaches it again and schedules the server->co_trip coroutine in the updated AioContext. However, nothing guarantees that server->co_trip is even safe to be scheduled. Not only is it unclear that the coroutine is actually in a state where it can be reentered externally without causing problems, but with two consecutive drains, it is possible that the scheduled coroutine didn't have a chance yet to run and trying to schedule an already scheduled coroutine a second time crashes with an assertion failure. Following the model of NBD, this commit makes the vhost-user-blk export shut down server->co_trip during drain so that resuming the export means creating and scheduling a new coroutine, which is always safe. There is one exception: If the drain call didn't poll (for example, this happens in the context of bdrv_graph_wrlock()), then the coroutine didn't have a chance to shut down. However, in this case the AioContext can't have changed; changing the AioContext always involves a polling drain. So in this case we can simply assert that the AioContext is unchanged and just leave the coroutine running or wake it up if it has yielded to wait for the AioContext to be attached again. Fixes: e1054cd4aad03a493a5d1cded7508f7c348205bf Fixes: https://issues.redhat.com/browse/RHEL-1708 Signed-off-by: Kevin Wolf --- include/qemu/vhost-user-server.h | 2 ++ block/export/vhost-user-blk-server.c | 9 +++++-- util/vhost-user-server.c | 36 +++++++++++++++++++++++----- 3 files changed, 39 insertions(+), 8 deletions(-) diff --git a/include/qemu/vhost-user-server.h b/include/qemu/vhost-user-ser= ver.h index 64ad701015..ca1713b53e 100644 --- a/include/qemu/vhost-user-server.h +++ b/include/qemu/vhost-user-server.h @@ -45,6 +45,8 @@ typedef struct { /* Protected by ctx lock */ bool in_qio_channel_yield; bool wait_idle; + bool quiescing; + bool wake_on_ctx_attach; VuDev vu_dev; QIOChannel *ioc; /* The I/O channel with the client */ QIOChannelSocket *sioc; /* The underlying data channel with the client= */ diff --git a/block/export/vhost-user-blk-server.c b/block/export/vhost-user= -blk-server.c index fe2cee3a78..16f48388d3 100644 --- a/block/export/vhost-user-blk-server.c +++ b/block/export/vhost-user-blk-server.c @@ -283,6 +283,7 @@ static void vu_blk_drained_begin(void *opaque) { VuBlkExport *vexp =3D opaque; =20 + vexp->vu_server.quiescing =3D true; vhost_user_server_detach_aio_context(&vexp->vu_server); } =20 @@ -291,19 +292,23 @@ static void vu_blk_drained_end(void *opaque) { VuBlkExport *vexp =3D opaque; =20 + vexp->vu_server.quiescing =3D false; vhost_user_server_attach_aio_context(&vexp->vu_server, vexp->export.ct= x); } =20 /* - * Ensures that bdrv_drained_begin() waits until in-flight requests comple= te. + * Ensures that bdrv_drained_begin() waits until in-flight requests comple= te + * and the server->co_trip coroutine has terminated. It will be restarted = in + * vhost_user_server_attach_aio_context(). * * Called with vexp->export.ctx acquired. */ static bool vu_blk_drained_poll(void *opaque) { VuBlkExport *vexp =3D opaque; + VuServer *server =3D &vexp->vu_server; =20 - return vhost_user_server_has_in_flight(&vexp->vu_server); + return server->co_trip || vhost_user_server_has_in_flight(server); } =20 static const BlockDevOps vu_blk_dev_ops =3D { diff --git a/util/vhost-user-server.c b/util/vhost-user-server.c index 5ccc6d24a0..23004d0c62 100644 --- a/util/vhost-user-server.c +++ b/util/vhost-user-server.c @@ -133,7 +133,9 @@ vu_message_read(VuDev *vu_dev, int conn_fd, VhostUserMs= g *vmsg) server->in_qio_channel_yield =3D false; } else { /* Wait until attached to an AioContext again */ + server->wake_on_ctx_attach =3D true; qemu_coroutine_yield(); + assert(!server->wake_on_ctx_attach); } continue; } else { @@ -201,8 +203,15 @@ static coroutine_fn void vu_client_trip(void *opaque) VuServer *server =3D opaque; VuDev *vu_dev =3D &server->vu_dev; =20 - while (!vu_dev->broken && vu_dispatch(vu_dev)) { - /* Keep running */ + while (!vu_dev->broken) { + if (server->quiescing) { + server->co_trip =3D NULL; + aio_wait_kick(); + return; + } + if (!vu_dispatch(vu_dev)) { + break; + } } =20 if (vhost_user_server_has_in_flight(server)) { @@ -353,8 +362,7 @@ static void vu_accept(QIONetListener *listener, QIOChan= nelSocket *sioc, =20 qio_channel_set_follow_coroutine_ctx(server->ioc, true); =20 - server->co_trip =3D qemu_coroutine_create(vu_client_trip, server); - + /* Attaching the AioContext starts the vu_client_trip coroutine */ aio_context_acquire(server->ctx); vhost_user_server_attach_aio_context(server, server->ctx); aio_context_release(server->ctx); @@ -413,8 +421,24 @@ void vhost_user_server_attach_aio_context(VuServer *se= rver, AioContext *ctx) NULL, NULL, vu_fd_watch); } =20 - assert(!server->in_qio_channel_yield); - aio_co_schedule(ctx, server->co_trip); + if (server->co_trip) { + /* + * The caller didn't fully shut down co_trip (this can happen on + * non-polling drains like in bdrv_graph_wrlock()). This is okay a= s long + * as it no longer tries to shut it down and we're guaranteed to s= till + * be in the same AioContext as before. + */ + assert(!server->quiescing); + assert(qemu_coroutine_get_aio_context(server->co_trip) =3D=3D ctx); + if (server->wake_on_ctx_attach) { + server->wake_on_ctx_attach =3D false; + aio_co_wake(server->co_trip); + } + } else { + server->co_trip =3D qemu_coroutine_create(vu_client_trip, server); + assert(!server->in_qio_channel_yield); + aio_co_schedule(ctx, server->co_trip); + } } =20 /* Called with server->ctx acquired */ --=20 2.42.0