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Re: [PATCH v2 2/6] vhost-user-blk: Don't reconnect during initialisation
From: |
Kevin Wolf |
Subject: |
Re: [PATCH v2 2/6] vhost-user-blk: Don't reconnect during initialisation |
Date: |
Tue, 4 May 2021 11:10:47 +0200 |
Am 03.05.2021 um 19:01 hat Raphael Norwitz geschrieben:
> So we're not going with the suggestion to retry once or a fixed number
> of times? Any reason why not?
I thought we agreed that we'd add reconnection back in a follow-up
series that also addresses the different kinds of errors and retries
only when it makes sense?
Kevin
> On Thu, Apr 29, 2021 at 07:13:12PM +0200, Kevin Wolf wrote:
> > This is a partial revert of commits 77542d43149 and bc79c87bcde.
> >
> > Usually, an error during initialisation means that the configuration was
> > wrong. Reconnecting won't make the error go away, but just turn the
> > error condition into an endless loop. Avoid this and return errors
> > again.
> >
> > Additionally, calling vhost_user_blk_disconnect() from the chardev event
> > handler could result in use-after-free because none of the
> > initialisation code expects that the device could just go away in the
> > middle. So removing the call fixes crashes in several places.
> >
> > For example, using a num-queues setting that is incompatible with the
> > backend would result in a crash like this (dereferencing dev->opaque,
> > which is already NULL):
> >
> > #0 0x0000555555d0a4bd in vhost_user_read_cb (source=0x5555568f4690,
> > condition=(G_IO_IN | G_IO_HUP), opaque=0x7fffffffcbf0) at
> > ../hw/virtio/vhost-user.c:313
> > #1 0x0000555555d950d3 in qio_channel_fd_source_dispatch
> > (source=0x555557c3f750, callback=0x555555d0a478 <vhost_user_read_cb>,
> > user_data=0x7fffffffcbf0) at ../io/channel-watch.c:84
> > #2 0x00007ffff7b32a9f in g_main_context_dispatch () at
> > /lib64/libglib-2.0.so.0
> > #3 0x00007ffff7b84a98 in g_main_context_iterate.constprop () at
> > /lib64/libglib-2.0.so.0
> > #4 0x00007ffff7b32163 in g_main_loop_run () at /lib64/libglib-2.0.so.0
> > #5 0x0000555555d0a724 in vhost_user_read (dev=0x555557bc62f8,
> > msg=0x7fffffffcc50) at ../hw/virtio/vhost-user.c:402
> > #6 0x0000555555d0ee6b in vhost_user_get_config (dev=0x555557bc62f8,
> > config=0x555557bc62ac "", config_len=60) at ../hw/virtio/vhost-user.c:2133
> > #7 0x0000555555d56d46 in vhost_dev_get_config (hdev=0x555557bc62f8,
> > config=0x555557bc62ac "", config_len=60) at ../hw/virtio/vhost.c:1566
> > #8 0x0000555555cdd150 in vhost_user_blk_device_realize
> > (dev=0x555557bc60b0, errp=0x7fffffffcf90) at
> > ../hw/block/vhost-user-blk.c:510
> > #9 0x0000555555d08f6d in virtio_device_realize (dev=0x555557bc60b0,
> > errp=0x7fffffffcff0) at ../hw/virtio/virtio.c:3660
> >
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> > hw/block/vhost-user-blk.c | 59 +++++++++++----------------------------
> > 1 file changed, 17 insertions(+), 42 deletions(-)
> >
> > diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> > index 7c85248a7b..c0b9958da1 100644
> > --- a/hw/block/vhost-user-blk.c
> > +++ b/hw/block/vhost-user-blk.c
> > @@ -50,6 +50,8 @@ static const int user_feature_bits[] = {
> > VHOST_INVALID_FEATURE_BIT
> > };
> >
> > +static void vhost_user_blk_event(void *opaque, QEMUChrEvent event);
> > +
> > static void vhost_user_blk_update_config(VirtIODevice *vdev, uint8_t
> > *config)
> > {
> > VHostUserBlk *s = VHOST_USER_BLK(vdev);
> > @@ -362,19 +364,6 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
> > vhost_dev_cleanup(&s->dev);
> > }
> >
> > -static void vhost_user_blk_event(void *opaque, QEMUChrEvent event,
> > - bool realized);
> > -
> > -static void vhost_user_blk_event_realize(void *opaque, QEMUChrEvent event)
> > -{
> > - vhost_user_blk_event(opaque, event, false);
> > -}
> > -
> > -static void vhost_user_blk_event_oper(void *opaque, QEMUChrEvent event)
> > -{
> > - vhost_user_blk_event(opaque, event, true);
> > -}
> > -
> > static void vhost_user_blk_chr_closed_bh(void *opaque)
> > {
> > DeviceState *dev = opaque;
> > @@ -382,12 +371,11 @@ static void vhost_user_blk_chr_closed_bh(void *opaque)
> > VHostUserBlk *s = VHOST_USER_BLK(vdev);
> >
> > vhost_user_blk_disconnect(dev);
> > - qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
> > - vhost_user_blk_event_oper, NULL, opaque, NULL, true);
> > + qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, vhost_user_blk_event,
> > + NULL, opaque, NULL, true);
> > }
> >
> > -static void vhost_user_blk_event(void *opaque, QEMUChrEvent event,
> > - bool realized)
> > +static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
> > {
> > DeviceState *dev = opaque;
> > VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> > @@ -401,17 +389,7 @@ static void vhost_user_blk_event(void *opaque,
> > QEMUChrEvent event,
> > }
> > break;
> > case CHR_EVENT_CLOSED:
> > - /*
> > - * Closing the connection should happen differently on device
> > - * initialization and operation stages.
> > - * On initalization, we want to re-start vhost_dev initialization
> > - * from the very beginning right away when the connection is
> > closed,
> > - * so we clean up vhost_dev on each connection closing.
> > - * On operation, we want to postpone vhost_dev cleanup to let the
> > - * other code perform its own cleanup sequence using vhost_dev data
> > - * (e.g. vhost_dev_set_log).
> > - */
> > - if (realized && !runstate_check(RUN_STATE_SHUTDOWN)) {
> > + 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
> > @@ -431,8 +409,6 @@ static void vhost_user_blk_event(void *opaque,
> > QEMUChrEvent event,
> > * knowing its type (in this case vhost-user).
> > */
> > s->dev.started = false;
> > - } else {
> > - vhost_user_blk_disconnect(dev);
> > }
> > break;
> > case CHR_EVENT_BREAK:
> > @@ -489,33 +465,32 @@ static void vhost_user_blk_device_realize(DeviceState
> > *dev, Error **errp)
> > s->vhost_vqs = g_new0(struct vhost_virtqueue, s->num_queues);
> > s->connected = false;
> >
> > - qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
> > - vhost_user_blk_event_realize, NULL, (void
> > *)dev,
> > - NULL, true);
> > -
> > -reconnect:
> > if (qemu_chr_fe_wait_connected(&s->chardev, errp) < 0) {
> > goto virtio_err;
> > }
> >
> > - /* check whether vhost_user_blk_connect() failed or not */
> > - if (!s->connected) {
> > - goto reconnect;
> > + if (vhost_user_blk_connect(dev) < 0) {
> > + error_setg(errp, "vhost-user-blk: could not connect");
> > + qemu_chr_fe_disconnect(&s->chardev);
> > + goto virtio_err;
> > }
> > + assert(s->connected);
> >
> > ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
> > sizeof(struct virtio_blk_config));
> > if (ret < 0) {
> > - error_report("vhost-user-blk: get block config failed");
> > - goto reconnect;
> > + error_setg(errp, "vhost-user-blk: get block config failed");
> > + goto vhost_err;
> > }
> >
> > - /* we're fully initialized, now we can operate, so change the handler
> > */
> > + /* we're fully initialized, now we can operate, so add the handler */
> > qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
> > - vhost_user_blk_event_oper, NULL, (void *)dev,
> > + vhost_user_blk_event, NULL, (void *)dev,
> > NULL, true);
> > return;
> >
> > +vhost_err:
> > + vhost_dev_cleanup(&s->dev);
> > virtio_err:
> > g_free(s->vhost_vqs);
> > s->vhost_vqs = NULL;
> > --
> > 2.30.2
> >
>