[Spice-devel] [PATCH] migration: Don't assert() if MIGRATE_DATA comes before attaching the agent
Christophe Fergeau
cfergeau at redhat.com
Thu Aug 7 09:03:17 PDT 2014
This is very close to the last iteration I sent, except that you moved
the dead code path my patch had to a more appropriate place ;) ACK,
though would be nice to have a reproducer in the commit log.
Christophe
On Wed, Jul 23, 2014 at 12:16:56AM +0300, Uri Lublin wrote:
> During seamless migration, after switching host, if a client was connected
> during the migration, it will have data to send back to the new
> qemu/spice-server instance. This is handled through MIGRATE_DATA messages.
> SPICE char devices use such MIGRATE_DATA messages to restore their state.
>
> However, the MIGRATE_DATA message can arrive any time after the new qemu
> instance has started, this can happen before or after the SPICE char
> devices have been created. In order to handle this, if the migrate data
> arrives early, it's stored in reds->agent_state.mig_data, and
> attach_to_red_agent() will restore the agent state as appropriate.
>
> Unfortunately this does not work as expected, for main
> channel (agent messages).
> If attach_to_red_agent() is called before the MIGRATE_DATA
> message reaches the server, all goes well,
> but if MIGRATE_DATA reaches the server before
> attach_to_red_agent() gets called, then some assert() gets
> triggered in spice_char_device_state_restore():
>
> ((null):32507): Spice-ERROR **: char_device.c:937:spice_char_device_state_restore: assertion `dev->num_clients == 1 && dev->wait_for_migrate_data' failed
> Thread 3 (Thread 0x7f406b543700 (LWP 32543)):
> Thread 2 (Thread 0x7f40697ff700 (LWP 32586)):
> Thread 1 (Thread 0x7f4079b45a40 (LWP 32507)):
>
> When restoring state, a client must already be added to the
> spice-char-device.
> What happens is that a client is not being added to the char-device
> when when MIGRATE_DATA arrives first, which leaves both
> dev->num_clients and dev->wait_for_migrate_data value at 0.
>
> This commit changes the logic in spice_server_char_device_add_interface(),
> such that if there is migrate data pending in reds->agent_state.mig_data
> but no client was added to the spice-char-device yet,
> then first the client is added to the device by calling
> spice_char_device_client_add(), and only then the state is restored.
>
> This fixes https://bugzilla.redhat.com/show_bug.cgi?id=1035184
>
> Based-on-a-patch-by: Christophe Fergeau <cfergeau at redhat.com>
> ---
> server/reds.c | 39 ++++++++++++++++++++++++++++-----------
> 1 file changed, 28 insertions(+), 11 deletions(-)
>
> diff --git a/server/reds.c b/server/reds.c
> index 2c437ac..ed142ec 100644
> --- a/server/reds.c
> +++ b/server/reds.c
> @@ -1274,6 +1274,7 @@ int reds_handle_migrate_data(MainChannelClient *mcc, SpiceMigrateDataMain *mig_d
> {
> VDIPortState *agent_state = &reds->agent_state;
>
> + spice_debug("main-channel: got migrate data");
> /*
> * Now that the client has switched to the target server, if main_channel
> * controls the mm-time, we update the client's mm-time.
> @@ -1295,15 +1296,18 @@ int reds_handle_migrate_data(MainChannelClient *mcc, SpiceMigrateDataMain *mig_d
> main_channel_push_agent_disconnected(reds->main_channel);
> main_channel_push_agent_connected(reds->main_channel);
> } else {
> + spice_debug("restoring state from mig_data");
> return reds_agent_state_restore(mig_data);
> }
> }
> } else {
> /* restore agent starte when the agent gets attached */
> + spice_debug("saving mig_data");
> spice_assert(agent_state->plug_generation == 0);
> agent_state->mig_data = spice_memdup(mig_data, size);
> }
> } else {
> + spice_debug("agent was not attached on the source host");
> if (vdagent) {
> /* spice_char_device_client_remove disables waiting for migration data */
> spice_char_device_client_remove(agent_state->base,
> @@ -2857,17 +2861,15 @@ static SpiceCharDeviceState *attach_to_red_agent(SpiceCharDeviceInstance *sin)
> state->read_filter.discard_all = FALSE;
> reds->agent_state.plug_generation++;
>
> - if (reds->agent_state.mig_data) {
> - spice_assert(reds->agent_state.plug_generation == 1);
> - reds_agent_state_restore(reds->agent_state.mig_data);
> - free(reds->agent_state.mig_data);
> - reds->agent_state.mig_data = NULL;
> - } else if (!red_channel_waits_for_migrate_data(&reds->main_channel->base)) {
> - /* we will assoicate the client with the char device, upon reds_on_main_agent_start,
> - * in response to MSGC_AGENT_START */
> - main_channel_push_agent_connected(reds->main_channel);
> - } else {
> - spice_debug("waiting for migration data");
> + if (reds->agent_state.mig_data ||
> + red_channel_waits_for_migrate_data(&reds->main_channel->base)) {
> + /* Migration in progress (code is running on the destination host):
> + * 1. Add the client to spice char device, if it was not already added.
> + * 2.a If this (qemu-kvm state load side of migration) happens first
> + * then wait for spice migration data to arrive. Otherwise
> + * 2.b If this happens second ==> we already have spice migrate data
> + * then restore state
> + */
> if (!spice_char_device_client_exists(reds->agent_state.base, reds_get_client())) {
> int client_added;
>
> @@ -2883,9 +2885,24 @@ static SpiceCharDeviceState *attach_to_red_agent(SpiceCharDeviceInstance *sin)
> spice_warning("failed to add client to agent");
> reds_disconnect();
> }
> + }
>
> + if (reds->agent_state.mig_data) {
> + spice_debug("restoring state from stored migration data");
> + spice_assert(reds->agent_state.plug_generation == 1);
> + reds_agent_state_restore(reds->agent_state.mig_data);
> + free(reds->agent_state.mig_data);
> + reds->agent_state.mig_data = NULL;
> + }
> + else {
> + spice_debug("waiting for migration data");
> }
> + } else {
> + /* we will associate the client with the char device, upon reds_on_main_agent_start,
> + * in response to MSGC_AGENT_START */
> + main_channel_push_agent_connected(reds->main_channel);
> }
> +
> return state->base;
> }
>
> --
> 1.9.3
>
> _______________________________________________
> Spice-devel mailing list
> Spice-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/spice-devel
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