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vhost-user-blk: Don't reconnect during initialisation
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This is a partial revert of commits 77542d4 and bc79c87.

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

Note that this removes the ability to reconnect during initialisation
(but not during operation) when there is no permanent error, but the
backend restarts, as the implementation was buggy. This feature can be
added back in a follow-up series after changing error paths to
distinguish cases where retrying could help from cases with permanent
errors.

Signed-off-by: Kevin Wolf <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>
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@kevmw
kevmw committed May 18, 2021
1 parent f267297 commit dabefdd
Showing 1 changed file with 17 additions and 42 deletions.
59 changes: 17 additions & 42 deletions hw/block/vhost-user-blk.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand Down Expand Up @@ -362,32 +364,18 @@ 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;
VirtIODevice *vdev = VIRTIO_DEVICE(dev);
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);
Expand All @@ -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
Expand All @@ -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:
Expand Down Expand Up @@ -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;
Expand Down

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