Re: [PATCH v3 7/7] hw/virtio: generalise CHR_EVENT_CLOSED handling

[Michael S. Tsirkin]

On Wed, Nov 30, 2022 at 10:25:58AM +0000, Alex Bennée wrote:
> 
> Raphael Norwitz <raphael.norwitz@nutanix.com> writes:
> 
> >> On Nov 29, 2022, at 12:30 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> >> 
> >> On Tue, Nov 29, 2022 at 05:18:58AM +0000, Raphael Norwitz wrote:
> >>>> On Nov 28, 2022, at 11:41 AM, Alex Bennée <alex.bennee@linaro.org> 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. virtio-user-blk already had this mechanism in place so
> >>> 
> >>> The mechanism was originally copied from virtio-net so we should
> >>> probably fix it there too. AFAICT calling vhost_user_async_close()
> >>> should work in net_vhost_user_event().
> >>> 
> >>> Otherwise the code looks good modulo a few nits. Happy to see the 
> >>> duplicated logic is being generalized.
> >> 
> >> If you do, separate patch pls and does not have to block this series.
> >
> > If the series is urgent my comments can be addressed later.
> 
> On the surface it looks similar but the vhost-net code doesn't deal in
> DeviceState opaques and also has invented a s->watch variable for
> manually removing gio sources. I'm not sure I'm confident I can
> re-factor this code and not break something so close to release.

OK, that's fair.

> >
> > Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> >
> >> 
> >>> 
> >>>> generalise it as a vhost-user helper function and use for both blk and
> >>>> gpio devices.
> >>>> 
> >>>> 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.
> >>>> 
> >>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> >>>> ---
> >>>> 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(-)
> >>>> 
> >>>> diff --git a/include/hw/virtio/vhost-user.h 
> >>>> b/include/hw/virtio/vhost-user.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, 
> >>>> CharBackend *chr, Error **errp);
> >>>> */
> >>>> void vhost_user_cleanup(VhostUserState *user);
> >>>> 
> >>>> +/**
> >>>> + * 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 
> >>>> *vhost,
> >>>> +                            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);
> >>>> 
> >>>>    vhost_dev_cleanup(&s->dev);
> >>>> -}
> >>>> 
> >>>> -static void vhost_user_blk_chr_closed_bh(void *opaque)
> >>>> -{
> >>>> -    DeviceState *dev = opaque;
> >>>> -    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> >>>> -    VHostUserBlk *s = 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_event,
> >>>> -                             NULL, opaque, NULL, true);
> >>>> +                             NULL, dev, NULL, true);
> >>>> }
> >>>> 
> >>>> static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
> >>>> @@ -398,33 +391,9 @@ static void vhost_user_blk_event(void *opaque, 
> >>>> QEMUChrEvent 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 = qemu_get_current_aio_context();
> >>>> -
> >>>> -            qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, NULL, 
> >>>> NULL,
> >>>> -                    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 
> >>>> 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 
> >>>> without
> >>>> -             * 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 = 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 75e28bcd3b..cd76287766 100644
> >>>> --- a/hw/virtio/vhost-user-gpio.c
> >>>> +++ b/hw/virtio/vhost-user-gpio.c
> >>>> @@ -239,6 +239,8 @@ static int vu_gpio_connect(DeviceState *dev, Error 
> >>>> **errp)
> >>>>    return 0;
> >>>> }
> >>>> 
> >>>> +static void vu_gpio_event(void *opaque, QEMUChrEvent event);
> >>>> +
> >>>> static void vu_gpio_disconnect(DeviceState *dev)
> >>>> {
> >>>>    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> >>>> @@ -251,6 +253,11 @@ static void vu_gpio_disconnect(DeviceState *dev)
> >>>> 
> >>>>    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);
> >>>> }
> >>>> 
> >>>> static void vu_gpio_event(void *opaque, QEMUChrEvent event)
> >>>> @@ -268,7 +275,9 @@ 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 = NULL;
> >>>> }
> >>>> 
> >>> 
> >>> nit: Extra space 
> >>> 
> >>>> +
> >>>> +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 = opaque;
> >>>> +    struct vhost_dev *vhost = 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 
> >>>> *vhost,
> >>>> +                            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 = qemu_get_current_aio_context();
> >>>> +        VhostAsyncCallback *data = g_new0(VhostAsyncCallback, 1);
> >>>> +
> >>>> +        /* Save data for the callback */
> >>>> +        data->cb = cb;
> >>>> +        data->dev = d;
> >>>> +        data->cd = chardev;
> >>>> +        data->vhost = 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
> >>> 
> >>> Not this change’s fault but we should fix up the grammar here i.e.
> >>> s/clean/cleaned/ and probably should be “disconnected in the
> >>> BH”…etc.
> >>> 
> >>>> +         * 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 
> >>>> without
> >>>> +         * 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 = false;
> >>>> +    }
> >>>> +}
> >>>> +
> >>>> static int vhost_user_dev_start(struct vhost_dev *dev, bool started)
> >>>> {
> >>>>    if (!virtio_has_feature(dev->protocol_features,
> >>>> -- 
> >>>> 2.34.1
> >>>> 
> >>> 
> >> 
> 
> 
> -- 
> Alex Bennée