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 3967FC43217 for ; Thu, 1 Dec 2022 17:13:22 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1p0n6r-0004Zm-8f; Thu, 01 Dec 2022 12:12:29 -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 1p0n6n-0004ZR-8U for qemu-devel@nongnu.org; Thu, 01 Dec 2022 12:12:26 -0500 Received: from mail-wr1-x430.google.com ([2a00:1450:4864:20::430]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1p0n6k-0002Ef-Ig for qemu-devel@nongnu.org; Thu, 01 Dec 2022 12:12:24 -0500 Received: by mail-wr1-x430.google.com with SMTP id f18so3775872wrj.5 for ; Thu, 01 Dec 2022 09:12:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=content-transfer-encoding:mime-version:message-id:in-reply-to:date :subject:cc:to:from:user-agent:references:from:to:cc:subject:date :message-id:reply-to; bh=koNXauXfdMq7Rx+XLTIO3C6tCrMLAJfLlMAFZC8GWQI=; b=Myc82jCFluGA81h4K8NzsPQXlOw0yBzKUNyAdPyiIHL3h1bWhliQ7jMzskD8zrgvRm k6XvXj9rObF0ri2TqtnblroEx07dsuyAnWcaKIyuWPCw0Z0CufMVRPv+zw8FndbLqvQA N1uzR4+UHUXBQqMUuLThrUT9hkyroQPhg4r28MQqPxUT6tymTX25dDB3kSiwNg/Fc3j3 uIaoXJZcsy+x6/obEoFloe6dCJoELvFtVkBqFWwBjhjMPnLysof0cLAtjxJLbzxPg0mB eBVjYH4W0H/DnorsLsFO1e0lJh7+De8GcayxYRM44j4f3QdR6j8QP1k/ZQPLrjm5I99Y Gjig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:in-reply-to:date :subject:cc:to:from:user-agent:references:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=koNXauXfdMq7Rx+XLTIO3C6tCrMLAJfLlMAFZC8GWQI=; b=U7AF7TyUPRcm3LQ0SgMwAXi+Y3yQ6RO+emP9vJCkKGwTxgn17btJnhKUiOLwbSBO3p lewqkIqjm9VFTVH5QS9pNAMvH3trKU+ZkBuluTqQNGFNvtBTKsbBOpWKMpAvuZuruiMO hy4T8vnoHOYaZMYsaqtane8drX/5G/aQSBtBDuCjXu4LhhUGfHzaJ5CKSxko6hKmG7pC Pi1+d6b8LzvJqgqcmzRV+JC0mTUqHR/UPpeEw63eWbisWfi4T8LbGjlGfunb73q0K7F3 P+XqfBXEdHoCyjxVks6HXkapPQlHo0otAjMeP8A7WAwU+kZVOKuy7LKVf3YKyIonSVMg 3aYA== X-Gm-Message-State: ANoB5pnvMDI4ye2OCXFXlh5wUwOSN2hzfIHc5pZVgusiljuoGsUUj+6F MUPSPXqhjUngOZxM4ime8CJsVw== X-Google-Smtp-Source: AA0mqf6MO5+opc4GIqsrGjeAwyBq/gufueO/4SUQ1mnKsjdZDwHvaA7GRhgEYf60xrSqR1UP8sNsRw== X-Received: by 2002:a5d:5187:0:b0:242:5ef:ce32 with SMTP id k7-20020a5d5187000000b0024205efce32mr20175920wrv.260.1669914740936; Thu, 01 Dec 2022 09:12:20 -0800 (PST) Received: from zen.linaroharston ([185.81.254.11]) by smtp.gmail.com with ESMTPSA id g11-20020a056000118b00b00225307f43fbsm5067095wrx.44.2022.12.01.09.12.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Dec 2022 09:12:20 -0800 (PST) Received: from zen (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id CA4E51FFB7; Thu, 1 Dec 2022 17:12:19 +0000 (GMT) References: <20221130112439.2527228-1-alex.bennee@linaro.org> <20221130112439.2527228-5-alex.bennee@linaro.org> User-agent: mu4e 1.9.3; emacs 29.0.60 From: Alex =?utf-8?Q?Benn=C3=A9e?= To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, slp@redhat.com, mst@redhat.com, marcandre.lureau@redhat.com, mathieu.poirier@linaro.org, viresh.kumar@linaro.org, sgarzare@redhat.com, Raphael Norwitz , Kevin Wolf , Hanna Reitz , "open list:Block layer core" Subject: Re: [PATCH v4 4/5] hw/virtio: generalise CHR_EVENT_CLOSED handling Date: Thu, 01 Dec 2022 17:05:06 +0000 In-reply-to: Message-ID: <87v8mvaw0c.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::430; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x430.google.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, 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 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 Stefan Hajnoczi writes: > [[PGP Signed Part:Undecided]] > On Wed, Nov 30, 2022 at 11:24:38AM +0000, Alex Benn=C3=A9e wrote: >> ..and use for both virtio-user-blk and virtio-user-gpio. This avoids >> the circular close by deferring shutdown due to disconnection until a >> later point. > > I thought re-entrancy was already avoided by Patch 3? No because vu_gpio_disconnect() gets called while we are in the process of tearing things down for the vu_gpio_stop(). As it hasn't disconnected yet we end up doing the teardown there: #2 0x0000557adbe04d56 in vu_gpio_disconnect (dev=3D0x557adf80d640) at ..= /../hw/virtio/vhost-user-gpio.c:255 #3 0x0000557adbe049bb in vu_gpio_event (opaque=3D0x557adf80d640, event= =3DCHR_EVENT_CLOSED) at ../../hw/virtio/vhost-user-gpio.c:274 #4 0x0000557adc0539ef in chr_be_event (s=3D0x557adea51f10, event=3DCHR_E= VENT_CLOSED) at ../../chardev/char.c:61 #5 0x0000557adc0506aa in qemu_chr_be_event (s=3D0x557adea51f10, event=3D= CHR_EVENT_CLOSED) at ../../chardev/char.c:81 #6 0x0000557adc04f666 in tcp_chr_disconnect_locked (chr=3D0x557adea51f10= ) at ../../chardev/char-socket.c:470 #7 0x0000557adc04c81a in tcp_chr_write (chr=3D0x557adea51f10, buf=3D0x7f= fe8588cce0 "\v", len=3D20) at ../../chardev/char-socket.c:129 #8 0x0000557adc050999 in qemu_chr_write_buffer (s=3D0x557adea51f10, buf= =3D0x7ffe8588cce0 "\v", len=3D20, offset=3D0x7ffe8588cbe4, write_all=3Dtrue= ) at ../../chardev/char.c:121 #9 0x0000557adc0507c7 in qemu_chr_write (s=3D0x557adea51f10, buf=3D0x7ff= e8588cce0 "\v", len=3D20, write_all=3Dtrue) at ../../chardev/char.c:173 #10 0x0000557adc046f3a in qemu_chr_fe_write_all (be=3D0x557adf80d830, buf= =3D0x7ffe8588cce0 "\v", len=3D20) at ../../chardev/char-fe.c:53 #11 0x0000557adbddc02f in vhost_user_write (dev=3D0x557adf80d878, msg=3D0= x7ffe8588cce0, fds=3D0x0, fd_num=3D0) at ../../hw/virtio/vhost-user.c:490 #12 0x0000557adbddd48f in vhost_user_get_vring_base (dev=3D0x557adf80d878= , ring=3D0x7ffe8588d000) at ../../hw/virtio/vhost-user.c:1260 #13 0x0000557adbdd4bd6 in vhost_virtqueue_stop (dev=3D0x557adf80d878, vde= v=3D0x557adf80d640, vq=3D0x557adf843570, idx=3D0) at ../../hw/virtio/vhost.= c:1220 #14 0x0000557adbdd7eda in vhost_dev_stop (hdev=3D0x557adf80d878, vdev=3D0= x557adf80d640, vrings=3Dfalse) at ../../hw/virtio/vhost.c:1916 #15 0x0000557adbe051a6 in vu_gpio_stop (vdev=3D0x557adf80d640) at ../../h= w/virtio/vhost-user-gpio.c:142 and when we finally return the disconnect event has wiped out vhost_user. > >> virtio-user-blk already had this mechanism in place so >> generalise it as a vhost-user helper function and use for both blk and >> gpio devices. >>=20 >> While we are at it we also fix up vhost-user-gpio to re-establish the >> event handler after close down so we can reconnect later. > > I don't understand how the BH is supposed to help. Normally BHs are used > to defer processing while we're in a call stack of some depth. The > callers still require the resource we want to free, so we scheduled a > BH. > > That's not the case here. The CHR_EVENT_CLOSED callback is just another > top-level event handler, not something that is called deep in a call > stack. Well it is in the shutdown case because as we write to the vhost_user backend to shut things down it dies and we immediately process the disconnect event. It is racy though so some times you get away with it. > This BH approach isn't safe against nested event loops (something that > calls aio_poll() to wait), because now the BH can be invoked deep in a > call stack. Well I did ask if anyone had any better suggestions. In this case I'm mostly just copying what vhost-user-blk did. > > That said, if Patch 3 isn't enough and this patch fixes a problem, then > let's keep it for 7.2. It feels like a possibly incomplete solution and > maybe something that should be solved differently in 8.0. > >>=20 >> Signed-off-by: Alex Benn=C3=A9e >> Reviewed-by: Michael S. Tsirkin >> Reviewed-by: Raphael Norwitz >> --- >> include/hw/virtio/vhost-user.h | 18 +++++++++ >> hw/block/vhost-user-blk.c | 41 +++----------------- >> hw/virtio/vhost-user-gpio.c | 11 +++++- >> hw/virtio/vhost-user.c | 71 ++++++++++++++++++++++++++++++++++ >> 4 files changed, 104 insertions(+), 37 deletions(-) >>=20 >> diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-us= er.h >> index c6e693cd3f..191216a74f 100644 >> --- a/include/hw/virtio/vhost-user.h >> +++ b/include/hw/virtio/vhost-user.h >> @@ -68,4 +68,22 @@ bool vhost_user_init(VhostUserState *user, CharBacken= d *chr, Error **errp); >> */ >> void vhost_user_cleanup(VhostUserState *user); >>=20=20 >> +/** >> + * vhost_user_async_close() - cleanup vhost-user post connection drop >> + * @d: DeviceState for the associated device (passed to callback) >> + * @chardev: the CharBackend associated with the connection >> + * @vhost: the common vhost device >> + * @cb: the user callback function to complete the clean-up >> + * >> + * This function is used to handle the shutdown of a vhost-user >> + * connection to a backend. We handle this centrally to make sure we >> + * do all the steps and handle potential races due to VM shutdowns. >> + * Once the connection is disabled we call a backhalf to ensure >> + */ >> +typedef void (*vu_async_close_fn)(DeviceState *cb); >> + >> +void vhost_user_async_close(DeviceState *d, >> + CharBackend *chardev, struct vhost_dev *vho= st, >> + vu_async_close_fn cb); >> + >> #endif >> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c >> index 1177064631..aff4d2b8cb 100644 >> --- a/hw/block/vhost-user-blk.c >> +++ b/hw/block/vhost-user-blk.c >> @@ -369,17 +369,10 @@ static void vhost_user_blk_disconnect(DeviceState = *dev) >> vhost_user_blk_stop(vdev); >>=20=20 >> vhost_dev_cleanup(&s->dev); >> -} >>=20=20 >> -static void vhost_user_blk_chr_closed_bh(void *opaque) >> -{ >> - DeviceState *dev =3D opaque; >> - VirtIODevice *vdev =3D VIRTIO_DEVICE(dev); >> - VHostUserBlk *s =3D VHOST_USER_BLK(vdev); >> - >> - vhost_user_blk_disconnect(dev); >> + /* Re-instate the event handler for new connections */ >> qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, vhost_user_blk_ev= ent, >> - NULL, opaque, NULL, true); >> + NULL, dev, NULL, true); >> } >>=20=20 >> static void vhost_user_blk_event(void *opaque, QEMUChrEvent event) >> @@ -398,33 +391,9 @@ static void vhost_user_blk_event(void *opaque, QEMU= ChrEvent event) >> } >> break; >> case CHR_EVENT_CLOSED: >> - if (!runstate_check(RUN_STATE_SHUTDOWN)) { >> - /* >> - * A close event may happen during a read/write, but vhost >> - * code assumes the vhost_dev remains setup, so delay the >> - * stop & clear. >> - */ >> - AioContext *ctx =3D qemu_get_current_aio_context(); >> - >> - qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, NULL, NUL= L, >> - NULL, NULL, false); >> - aio_bh_schedule_oneshot(ctx, vhost_user_blk_chr_closed_bh, = opaque); >> - >> - /* >> - * Move vhost device to the stopped state. The vhost-user d= evice >> - * will be clean up and disconnected in BH. This can be use= ful in >> - * the vhost migration code. If disconnect was caught there= is an >> - * option for the general vhost code to get the dev state w= ithout >> - * knowing its type (in this case vhost-user). >> - * >> - * FIXME: this is sketchy to be reaching into vhost_dev >> - * now because we are forcing something that implies we >> - * have executed vhost_dev_stop() but that won't happen >> - * until vhost_user_blk_stop() gets called from the bh. >> - * Really this state check should be tracked locally. >> - */ >> - s->dev.started =3D false; >> - } >> + /* defer close until later to avoid circular close */ >> + vhost_user_async_close(dev, &s->chardev, &s->dev, >> + vhost_user_blk_disconnect); >> break; >> case CHR_EVENT_BREAK: >> case CHR_EVENT_MUX_IN: >> diff --git a/hw/virtio/vhost-user-gpio.c b/hw/virtio/vhost-user-gpio.c >> index be9be08b4c..b7b82a1099 100644 >> --- a/hw/virtio/vhost-user-gpio.c >> +++ b/hw/virtio/vhost-user-gpio.c >> @@ -233,6 +233,8 @@ static int vu_gpio_connect(DeviceState *dev, Error *= *errp) >> return 0; >> } >>=20=20 >> +static void vu_gpio_event(void *opaque, QEMUChrEvent event); >> + >> static void vu_gpio_disconnect(DeviceState *dev) >> { >> VirtIODevice *vdev =3D VIRTIO_DEVICE(dev); >> @@ -245,6 +247,11 @@ static void vu_gpio_disconnect(DeviceState *dev) >>=20=20 >> vu_gpio_stop(vdev); >> vhost_dev_cleanup(&gpio->vhost_dev); >> + >> + /* Re-instate the event handler for new connections */ >> + qemu_chr_fe_set_handlers(&gpio->chardev, >> + NULL, NULL, vu_gpio_event, >> + NULL, dev, NULL, true); >> } >>=20=20 >> static void vu_gpio_event(void *opaque, QEMUChrEvent event) >> @@ -262,7 +269,9 @@ static void vu_gpio_event(void *opaque, QEMUChrEvent= event) >> } >> break; >> case CHR_EVENT_CLOSED: >> - vu_gpio_disconnect(dev); >> + /* defer close until later to avoid circular close */ >> + vhost_user_async_close(dev, &gpio->chardev, &gpio->vhost_dev, >> + vu_gpio_disconnect); >> break; >> case CHR_EVENT_BREAK: >> case CHR_EVENT_MUX_IN: >> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c >> index abe23d4ebe..8f635844af 100644 >> --- a/hw/virtio/vhost-user.c >> +++ b/hw/virtio/vhost-user.c >> @@ -21,6 +21,7 @@ >> #include "qemu/error-report.h" >> #include "qemu/main-loop.h" >> #include "qemu/sockets.h" >> +#include "sysemu/runstate.h" >> #include "sysemu/cryptodev.h" >> #include "migration/migration.h" >> #include "migration/postcopy-ram.h" >> @@ -2670,6 +2671,76 @@ void vhost_user_cleanup(VhostUserState *user) >> user->chr =3D NULL; >> } >>=20=20 >> + >> +typedef struct { >> + vu_async_close_fn cb; >> + DeviceState *dev; >> + CharBackend *cd; >> + struct vhost_dev *vhost; >> +} VhostAsyncCallback; >> + >> +static void vhost_user_async_close_bh(void *opaque) >> +{ >> + VhostAsyncCallback *data =3D opaque; >> + struct vhost_dev *vhost =3D data->vhost; >> + >> + /* >> + * If the vhost_dev has been cleared in the meantime there is >> + * nothing left to do as some other path has completed the >> + * cleanup. >> + */ >> + if (vhost->vdev) { >> + data->cb(data->dev); >> + } >> + >> + g_free(data); >> +} >> + >> +/* >> + * We only schedule the work if the machine is running. If suspended >> + * we want to keep all the in-flight data as is for migration >> + * purposes. >> + */ >> +void vhost_user_async_close(DeviceState *d, >> + CharBackend *chardev, struct vhost_dev *vho= st, >> + vu_async_close_fn cb) >> +{ >> + if (!runstate_check(RUN_STATE_SHUTDOWN)) { >> + /* >> + * A close event may happen during a read/write, but vhost >> + * code assumes the vhost_dev remains setup, so delay the >> + * stop & clear. >> + */ >> + AioContext *ctx =3D qemu_get_current_aio_context(); >> + VhostAsyncCallback *data =3D g_new0(VhostAsyncCallback, 1); >> + >> + /* Save data for the callback */ >> + data->cb =3D cb; >> + data->dev =3D d; >> + data->cd =3D chardev; >> + data->vhost =3D vhost; >> + >> + /* Disable any further notifications on the chardev */ >> + qemu_chr_fe_set_handlers(chardev, >> + NULL, NULL, NULL, NULL, NULL, NULL, >> + false); >> + >> + aio_bh_schedule_oneshot(ctx, vhost_user_async_close_bh, data); >> + >> + /* >> + * Move vhost device to the stopped state. The vhost-user device >> + * will be clean up and disconnected in BH. This can be useful = in >> + * the vhost migration code. If disconnect was caught there is = an >> + * option for the general vhost code to get the dev state witho= ut >> + * knowing its type (in this case vhost-user). >> + * >> + * Note if the vhost device is fully cleared by the time we >> + * execute the bottom half we won't continue with the cleanup. >> + */ >> + vhost->started =3D false; >> + } >> +} >> + >> static int vhost_user_dev_start(struct vhost_dev *dev, bool started) >> { >> if (!virtio_has_feature(dev->protocol_features, >> --=20 >> 2.34.1 >>=20 > > [[End of PGP Signed Part]] --=20 Alex Benn=C3=A9e