From nobody Tue Feb 10 04:15:47 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1623790247987638.4874794983909; Tue, 15 Jun 2021 13:50:47 -0700 (PDT) Received: from localhost ([::1]:44956 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ltG1G-0006Hx-T3 for importer@patchew.org; Tue, 15 Jun 2021 16:50:46 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58048) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ltFyu-00026n-DE for qemu-devel@nongnu.org; Tue, 15 Jun 2021 16:48:20 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:26455) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ltFyr-00013K-C3 for qemu-devel@nongnu.org; Tue, 15 Jun 2021 16:48:20 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-517-cBJXQwFONKKXbCXgIvY21Q-1; Tue, 15 Jun 2021 16:48:15 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EA9FB100C618; Tue, 15 Jun 2021 20:48:13 +0000 (UTC) Received: from blue.redhat.com (ovpn-114-191.phx2.redhat.com [10.3.114.191]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8051E5D9CA; Tue, 15 Jun 2021 20:48:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1623790096; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9qw15AXj1YNaf+iLy2ksTn4Zvh/VDMB0WF+Nxw4PTbk=; b=fDb5OtPMn2dtXVU0Ru1vmDxFUP+qplzBUzYGkb75Py1UH87bjlv0zq/qEDtMlGsRCrVxsO KfaCGvfr5+E/2Y5M5LXoil1OFBQB5rqZFIWTV2mH3CjTYx/ituOut3PoOufu5+YNfTPUIF 1eVrE/iSLftciwkKI7NpdXePFGwZFfE= X-MC-Unique: cBJXQwFONKKXbCXgIvY21Q-1 From: Eric Blake To: qemu-devel@nongnu.org Subject: [PULL 12/34] block/nbd: simplify waking of nbd_co_establish_connection() Date: Tue, 15 Jun 2021 15:47:34 -0500 Message-Id: <20210615204756.281505-13-eblake@redhat.com> In-Reply-To: <20210615204756.281505-1-eblake@redhat.com> References: <20210615204756.281505-1-eblake@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable 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=216.205.24.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.197, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Vladimir Sementsov-Ogievskiy , "open list:Network Block Dev..." , Max Reitz Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" From: Vladimir Sementsov-Ogievskiy Instead of managing connect_bh, bh_ctx, and wait_connect fields, we can use a single link to the waiting coroutine with proper mutex protection. So new logic is: nbd_co_establish_connection() sets wait_co under the mutex, releases the mutex, then yield()s. Note that wait_co may be scheduled by the thread immediately after unlocking the mutex. Still, the main thread (or iothread) will not reach the code for entering the coroutine until the yield(), so we are safe. connect_thread_func() and nbd_co_establish_connection_cancel() do the following to handle wait_co: Under the mutex, if thr->wait_co is not NULL, make it NULL and schedule it. This way, we avoid scheduling the coroutine twice. Still scheduling is a bit different: In connect_thread_func() we can just call aio_co_wake under mutex, after commit [async: the main AioContext is only "current" if under the BQL] we are sure that aio_co_wake() will not try to acquire the aio context and do qemu_aio_coroutine_enter() but simply schedule the coroutine by aio_co_schedule(). nbd_co_establish_connection_cancel() will be called from non-coroutine context in further patch and will be able to go through qemu_aio_coroutine_enter() path of aio_co_wake(). So keep current behavior of waking the coroutine after the critical section. Also, this commit reduces the dependence of nbd_co_establish_connection() on the internals of bs (we now use a generic pointer to the coroutine, instead of direct use of s->connection_co). This is a step towards splitting the connection API out of nbd.c. Signed-off-by: Vladimir Sementsov-Ogievskiy Message-Id: <20210610100802.5888-11-vsementsov@virtuozzo.com> Reviewied-by: Eric Blake Signed-off-by: Eric Blake --- block/nbd.c | 55 +++++++++++++++-------------------------------------- 1 file changed, 15 insertions(+), 40 deletions(-) diff --git a/block/nbd.c b/block/nbd.c index fdfb1ff7a158..653af629408d 100644 --- a/block/nbd.c +++ b/block/nbd.c @@ -87,12 +87,6 @@ typedef enum NBDConnectThreadState { typedef struct NBDConnectThread { /* Initialization constants */ SocketAddress *saddr; /* address to connect to */ - /* - * Bottom half to schedule on completion. Scheduled only if bh_ctx is = not - * NULL - */ - QEMUBHFunc *bh_func; - void *bh_opaque; /* * Result of last attempt. Valid in FAIL and SUCCESS states. @@ -101,10 +95,15 @@ typedef struct NBDConnectThread { QIOChannelSocket *sioc; Error *err; - /* state and bh_ctx are protected by mutex */ QemuMutex mutex; + /* All further fields are protected by mutex */ NBDConnectThreadState state; /* current state of the thread */ - AioContext *bh_ctx; /* where to schedule bh (NULL means don't schedule= ) */ + + /* + * wait_co: if non-NULL, which coroutine to wake in + * nbd_co_establish_connection() after yield() + */ + Coroutine *wait_co; } NBDConnectThread; typedef struct BDRVNBDState { @@ -138,7 +137,6 @@ typedef struct BDRVNBDState { char *x_dirty_bitmap; bool alloc_depth; - bool wait_connect; NBDConnectThread *connect_thread; } BDRVNBDState; @@ -370,15 +368,6 @@ static bool nbd_client_connecting_wait(BDRVNBDState *s) return qatomic_load_acquire(&s->state) =3D=3D NBD_CLIENT_CONNECTING_WA= IT; } -static void connect_bh(void *opaque) -{ - BDRVNBDState *state =3D opaque; - - assert(state->wait_connect); - state->wait_connect =3D false; - aio_co_wake(state->connection_co); -} - static void nbd_init_connect_thread(BDRVNBDState *s) { s->connect_thread =3D g_new(NBDConnectThread, 1); @@ -386,8 +375,6 @@ static void nbd_init_connect_thread(BDRVNBDState *s) *s->connect_thread =3D (NBDConnectThread) { .saddr =3D QAPI_CLONE(SocketAddress, s->saddr), .state =3D CONNECT_THREAD_NONE, - .bh_func =3D connect_bh, - .bh_opaque =3D s, }; qemu_mutex_init(&s->connect_thread->mutex); @@ -427,11 +414,9 @@ static void *connect_thread_func(void *opaque) switch (thr->state) { case CONNECT_THREAD_RUNNING: thr->state =3D ret < 0 ? CONNECT_THREAD_FAIL : CONNECT_THREAD_SUCC= ESS; - if (thr->bh_ctx) { - aio_bh_schedule_oneshot(thr->bh_ctx, thr->bh_func, thr->bh_opa= que); - - /* play safe, don't reuse bh_ctx on further connection attempt= s */ - thr->bh_ctx =3D NULL; + if (thr->wait_co) { + aio_co_wake(thr->wait_co); + thr->wait_co =3D NULL; } break; case CONNECT_THREAD_RUNNING_DETACHED: @@ -485,20 +470,14 @@ nbd_co_establish_connection(BlockDriverState *bs, Err= or **errp) abort(); } - thr->bh_ctx =3D qemu_get_current_aio_context(); + thr->wait_co =3D qemu_coroutine_self(); qemu_mutex_unlock(&thr->mutex); - /* * We are going to wait for connect-thread finish, but * nbd_client_co_drain_begin() can interrupt. - * - * Note that wait_connect variable is not visible for connect-thread. = It - * doesn't need mutex protection, it used only inside home aio context= of - * bs. */ - s->wait_connect =3D true; qemu_coroutine_yield(); qemu_mutex_lock(&thr->mutex); @@ -553,23 +532,19 @@ static void nbd_co_establish_connection_cancel(BlockD= riverState *bs) { BDRVNBDState *s =3D bs->opaque; NBDConnectThread *thr =3D s->connect_thread; - bool wake =3D false; + Coroutine *wait_co =3D NULL; qemu_mutex_lock(&thr->mutex); if (thr->state =3D=3D CONNECT_THREAD_RUNNING) { /* We can cancel only in running state, when bh is not yet schedul= ed */ - thr->bh_ctx =3D NULL; - if (s->wait_connect) { - s->wait_connect =3D false; - wake =3D true; - } + wait_co =3D g_steal_pointer(&thr->wait_co); } qemu_mutex_unlock(&thr->mutex); - if (wake) { - aio_co_wake(s->connection_co); + if (wait_co) { + aio_co_wake(wait_co); } } --=20 2.31.1