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qemu-e2k/migration/colo.c
Fam Zheng a1fbe750fd migration: Fix race of image locking between src and dst 
Previously, dst side will immediately try to lock the write byte upon
receiving QEMU_VM_EOF, but at src side, bdrv_inactivate_all() is only
done after sending it. If the src host is under load, dst may fail to
acquire the lock due to racing with the src unlocking it.

Fix this by hoisting the bdrv_inactivate_all() operation before
QEMU_VM_EOF.

N.B. A further improvement could possibly be done to cleanly handover
locks between src and dst, so that there is no window where a third QEMU
could steal the locks and prevent src and dst from running.

N.B. This commit includes a minor improvement to the error handling
by using qemu_file_set_error().

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Fam Zheng <famz@redhat.com>
Message-id: 20170616160658.32290-1-famz@redhat.com
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
[PMM: noted qemu_file_set_error() use in commit as suggested by Daniel]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
2017-06-19 17:53:33 +01:00

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/*
* COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
* (a.k.a. Fault Tolerance or Continuous Replication)
*
* Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
* Copyright (c) 2016 FUJITSU LIMITED
* Copyright (c) 2016 Intel Corporation
*
* This work is licensed under the terms of the GNU GPL, version 2 or
* later. See the COPYING file in the top-level directory.
*/
#include "qemu/osdep.h"
#include "sysemu/sysemu.h"
#include "qemu-file-channel.h"
#include "migration.h"
#include "qemu-file.h"
#include "savevm.h"
#include "migration/colo.h"
#include "block.h"
#include "io/channel-buffer.h"
#include "trace.h"
#include "qemu/error-report.h"
#include "migration/failover.h"
#include "replication.h"
#include "qmp-commands.h"
static bool vmstate_loading;
#define COLO_BUFFER_BASE_SIZE (4 * 1024 * 1024)
bool colo_supported(void)
{
return true;
}
bool migration_in_colo_state(void)
{
MigrationState *s = migrate_get_current();
return (s->state == MIGRATION_STATUS_COLO);
}
bool migration_incoming_in_colo_state(void)
{
MigrationIncomingState *mis = migration_incoming_get_current();
return mis && (mis->state == MIGRATION_STATUS_COLO);
}
static bool colo_runstate_is_stopped(void)
{
return runstate_check(RUN_STATE_COLO) || !runstate_is_running();
}
static void secondary_vm_do_failover(void)
{
int old_state;
MigrationIncomingState *mis = migration_incoming_get_current();
/* Can not do failover during the process of VM's loading VMstate, Or
* it will break the secondary VM.
*/
if (vmstate_loading) {
old_state = failover_set_state(FAILOVER_STATUS_ACTIVE,
FAILOVER_STATUS_RELAUNCH);
if (old_state != FAILOVER_STATUS_ACTIVE) {
error_report("Unknown error while do failover for secondary VM,"
"old_state: %s", FailoverStatus_lookup[old_state]);
}
return;
}
migrate_set_state(&mis->state, MIGRATION_STATUS_COLO,
MIGRATION_STATUS_COMPLETED);
if (!autostart) {
error_report("\"-S\" qemu option will be ignored in secondary side");
/* recover runstate to normal migration finish state */
autostart = true;
}
/*
* Make sure COLO incoming thread not block in recv or send,
* If mis->from_src_file and mis->to_src_file use the same fd,
* The second shutdown() will return -1, we ignore this value,
* It is harmless.
*/
if (mis->from_src_file) {
qemu_file_shutdown(mis->from_src_file);
}
if (mis->to_src_file) {
qemu_file_shutdown(mis->to_src_file);
}
old_state = failover_set_state(FAILOVER_STATUS_ACTIVE,
FAILOVER_STATUS_COMPLETED);
if (old_state != FAILOVER_STATUS_ACTIVE) {
error_report("Incorrect state (%s) while doing failover for "
"secondary VM", FailoverStatus_lookup[old_state]);
return;
}
/* Notify COLO incoming thread that failover work is finished */
qemu_sem_post(&mis->colo_incoming_sem);
/* For Secondary VM, jump to incoming co */
if (mis->migration_incoming_co) {
qemu_coroutine_enter(mis->migration_incoming_co);
}
}
static void primary_vm_do_failover(void)
{
MigrationState *s = migrate_get_current();
int old_state;
migrate_set_state(&s->state, MIGRATION_STATUS_COLO,
MIGRATION_STATUS_COMPLETED);
/*
* Wake up COLO thread which may blocked in recv() or send(),
* The s->rp_state.from_dst_file and s->to_dst_file may use the
* same fd, but we still shutdown the fd for twice, it is harmless.
*/
if (s->to_dst_file) {
qemu_file_shutdown(s->to_dst_file);
}
if (s->rp_state.from_dst_file) {
qemu_file_shutdown(s->rp_state.from_dst_file);
}
old_state = failover_set_state(FAILOVER_STATUS_ACTIVE,
FAILOVER_STATUS_COMPLETED);
if (old_state != FAILOVER_STATUS_ACTIVE) {
error_report("Incorrect state (%s) while doing failover for Primary VM",
FailoverStatus_lookup[old_state]);
return;
}
/* Notify COLO thread that failover work is finished */
qemu_sem_post(&s->colo_exit_sem);
}
void colo_do_failover(MigrationState *s)
{
/* Make sure VM stopped while failover happened. */
if (!colo_runstate_is_stopped()) {
vm_stop_force_state(RUN_STATE_COLO);
}
if (get_colo_mode() == COLO_MODE_PRIMARY) {
primary_vm_do_failover();
} else {
secondary_vm_do_failover();
}
}
void qmp_xen_set_replication(bool enable, bool primary,
bool has_failover, bool failover,
Error **errp)
{
#ifdef CONFIG_REPLICATION
ReplicationMode mode = primary ?
REPLICATION_MODE_PRIMARY :
REPLICATION_MODE_SECONDARY;
if (has_failover && enable) {
error_setg(errp, "Parameter 'failover' is only for"
" stopping replication");
return;
}
if (enable) {
replication_start_all(mode, errp);
} else {
if (!has_failover) {
failover = NULL;
}
replication_stop_all(failover, failover ? NULL : errp);
}
#else
abort();
#endif
}
ReplicationStatus *qmp_query_xen_replication_status(Error **errp)
{
#ifdef CONFIG_REPLICATION
Error *err = NULL;
ReplicationStatus *s = g_new0(ReplicationStatus, 1);
replication_get_error_all(&err);
if (err) {
s->error = true;
s->has_desc = true;
s->desc = g_strdup(error_get_pretty(err));
} else {
s->error = false;
}
error_free(err);
return s;
#else
abort();
#endif
}
void qmp_xen_colo_do_checkpoint(Error **errp)
{
#ifdef CONFIG_REPLICATION
replication_do_checkpoint_all(errp);
#else
abort();
#endif
}
static void colo_send_message(QEMUFile *f, COLOMessage msg,
Error **errp)
{
int ret;
if (msg >= COLO_MESSAGE__MAX) {
error_setg(errp, "%s: Invalid message", __func__);
return;
}
qemu_put_be32(f, msg);
qemu_fflush(f);
ret = qemu_file_get_error(f);
if (ret < 0) {
error_setg_errno(errp, -ret, "Can't send COLO message");
}
trace_colo_send_message(COLOMessage_lookup[msg]);
}
static void colo_send_message_value(QEMUFile *f, COLOMessage msg,
uint64_t value, Error **errp)
{
Error *local_err = NULL;
int ret;
colo_send_message(f, msg, &local_err);
if (local_err) {
error_propagate(errp, local_err);
return;
}
qemu_put_be64(f, value);
qemu_fflush(f);
ret = qemu_file_get_error(f);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to send value for message:%s",
COLOMessage_lookup[msg]);
}
}
static COLOMessage colo_receive_message(QEMUFile *f, Error **errp)
{
COLOMessage msg;
int ret;
msg = qemu_get_be32(f);
ret = qemu_file_get_error(f);
if (ret < 0) {
error_setg_errno(errp, -ret, "Can't receive COLO message");
return msg;
}
if (msg >= COLO_MESSAGE__MAX) {
error_setg(errp, "%s: Invalid message", __func__);
return msg;
}
trace_colo_receive_message(COLOMessage_lookup[msg]);
return msg;
}
static void colo_receive_check_message(QEMUFile *f, COLOMessage expect_msg,
Error **errp)
{
COLOMessage msg;
Error *local_err = NULL;
msg = colo_receive_message(f, &local_err);
if (local_err) {
error_propagate(errp, local_err);
return;
}
if (msg != expect_msg) {
error_setg(errp, "Unexpected COLO message %d, expected %d",
msg, expect_msg);
}
}
static uint64_t colo_receive_message_value(QEMUFile *f, uint32_t expect_msg,
Error **errp)
{
Error *local_err = NULL;
uint64_t value;
int ret;
colo_receive_check_message(f, expect_msg, &local_err);
if (local_err) {
error_propagate(errp, local_err);
return 0;
}
value = qemu_get_be64(f);
ret = qemu_file_get_error(f);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to get value for COLO message: %s",
COLOMessage_lookup[expect_msg]);
}
return value;
}
static int colo_do_checkpoint_transaction(MigrationState *s,
QIOChannelBuffer *bioc,
QEMUFile *fb)
{
Error *local_err = NULL;
int ret = -1;
colo_send_message(s->to_dst_file, COLO_MESSAGE_CHECKPOINT_REQUEST,
&local_err);
if (local_err) {
goto out;
}
colo_receive_check_message(s->rp_state.from_dst_file,
COLO_MESSAGE_CHECKPOINT_REPLY, &local_err);
if (local_err) {
goto out;
}
/* Reset channel-buffer directly */
qio_channel_io_seek(QIO_CHANNEL(bioc), 0, 0, NULL);
bioc->usage = 0;
qemu_mutex_lock_iothread();
if (failover_get_state() != FAILOVER_STATUS_NONE) {
qemu_mutex_unlock_iothread();
goto out;
}
vm_stop_force_state(RUN_STATE_COLO);
qemu_mutex_unlock_iothread();
trace_colo_vm_state_change("run", "stop");
/*
* Failover request bh could be called after vm_stop_force_state(),
* So we need check failover_request_is_active() again.
*/
if (failover_get_state() != FAILOVER_STATUS_NONE) {
goto out;
}
/* Disable block migration */
migrate_set_block_enabled(false, &local_err);
qemu_savevm_state_header(fb);
qemu_savevm_state_begin(fb);
qemu_mutex_lock_iothread();
qemu_savevm_state_complete_precopy(fb, false, false);
qemu_mutex_unlock_iothread();
qemu_fflush(fb);
colo_send_message(s->to_dst_file, COLO_MESSAGE_VMSTATE_SEND, &local_err);
if (local_err) {
goto out;
}
/*
* We need the size of the VMstate data in Secondary side,
* With which we can decide how much data should be read.
*/
colo_send_message_value(s->to_dst_file, COLO_MESSAGE_VMSTATE_SIZE,
bioc->usage, &local_err);
if (local_err) {
goto out;
}
qemu_put_buffer(s->to_dst_file, bioc->data, bioc->usage);
qemu_fflush(s->to_dst_file);
ret = qemu_file_get_error(s->to_dst_file);
if (ret < 0) {
goto out;
}
colo_receive_check_message(s->rp_state.from_dst_file,
COLO_MESSAGE_VMSTATE_RECEIVED, &local_err);
if (local_err) {
goto out;
}
colo_receive_check_message(s->rp_state.from_dst_file,
COLO_MESSAGE_VMSTATE_LOADED, &local_err);
if (local_err) {
goto out;
}
ret = 0;
qemu_mutex_lock_iothread();
vm_start();
qemu_mutex_unlock_iothread();
trace_colo_vm_state_change("stop", "run");
out:
if (local_err) {
error_report_err(local_err);
}
return ret;
}
static void colo_process_checkpoint(MigrationState *s)
{
QIOChannelBuffer *bioc;
QEMUFile *fb = NULL;
int64_t current_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
Error *local_err = NULL;
int ret;
failover_init_state();
s->rp_state.from_dst_file = qemu_file_get_return_path(s->to_dst_file);
if (!s->rp_state.from_dst_file) {
error_report("Open QEMUFile from_dst_file failed");
goto out;
}
/*
* Wait for Secondary finish loading VM states and enter COLO
* restore.
*/
colo_receive_check_message(s->rp_state.from_dst_file,
COLO_MESSAGE_CHECKPOINT_READY, &local_err);
if (local_err) {
goto out;
}
bioc = qio_channel_buffer_new(COLO_BUFFER_BASE_SIZE);
fb = qemu_fopen_channel_output(QIO_CHANNEL(bioc));
object_unref(OBJECT(bioc));
qemu_mutex_lock_iothread();
vm_start();
qemu_mutex_unlock_iothread();
trace_colo_vm_state_change("stop", "run");
timer_mod(s->colo_delay_timer,
current_time + s->parameters.x_checkpoint_delay);
while (s->state == MIGRATION_STATUS_COLO) {
if (failover_get_state() != FAILOVER_STATUS_NONE) {
error_report("failover request");
goto out;
}
qemu_sem_wait(&s->colo_checkpoint_sem);
ret = colo_do_checkpoint_transaction(s, bioc, fb);
if (ret < 0) {
goto out;
}
}
out:
/* Throw the unreported error message after exited from loop */
if (local_err) {
error_report_err(local_err);
}
if (fb) {
qemu_fclose(fb);
}
timer_del(s->colo_delay_timer);
/* Hope this not to be too long to wait here */
qemu_sem_wait(&s->colo_exit_sem);
qemu_sem_destroy(&s->colo_exit_sem);
/*
* Must be called after failover BH is completed,
* Or the failover BH may shutdown the wrong fd that
* re-used by other threads after we release here.
*/
if (s->rp_state.from_dst_file) {
qemu_fclose(s->rp_state.from_dst_file);
}
}
void colo_checkpoint_notify(void *opaque)
{
MigrationState *s = opaque;
int64_t next_notify_time;
qemu_sem_post(&s->colo_checkpoint_sem);
s->colo_checkpoint_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
next_notify_time = s->colo_checkpoint_time +
s->parameters.x_checkpoint_delay;
timer_mod(s->colo_delay_timer, next_notify_time);
}
void migrate_start_colo_process(MigrationState *s)
{
qemu_mutex_unlock_iothread();
qemu_sem_init(&s->colo_checkpoint_sem, 0);
s->colo_delay_timer = timer_new_ms(QEMU_CLOCK_HOST,
colo_checkpoint_notify, s);
qemu_sem_init(&s->colo_exit_sem, 0);
migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
MIGRATION_STATUS_COLO);
colo_process_checkpoint(s);
qemu_mutex_lock_iothread();
}
static void colo_wait_handle_message(QEMUFile *f, int *checkpoint_request,
Error **errp)
{
COLOMessage msg;
Error *local_err = NULL;
msg = colo_receive_message(f, &local_err);
if (local_err) {
error_propagate(errp, local_err);
return;
}
switch (msg) {
case COLO_MESSAGE_CHECKPOINT_REQUEST:
*checkpoint_request = 1;
break;
default:
*checkpoint_request = 0;
error_setg(errp, "Got unknown COLO message: %d", msg);
break;
}
}
void *colo_process_incoming_thread(void *opaque)
{
MigrationIncomingState *mis = opaque;
QEMUFile *fb = NULL;
QIOChannelBuffer *bioc = NULL; /* Cache incoming device state */
uint64_t total_size;
uint64_t value;
Error *local_err = NULL;
qemu_sem_init(&mis->colo_incoming_sem, 0);
migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
MIGRATION_STATUS_COLO);
failover_init_state();
mis->to_src_file = qemu_file_get_return_path(mis->from_src_file);
if (!mis->to_src_file) {
error_report("COLO incoming thread: Open QEMUFile to_src_file failed");
goto out;
}
/*
* Note: the communication between Primary side and Secondary side
* should be sequential, we set the fd to unblocked in migration incoming
* coroutine, and here we are in the COLO incoming thread, so it is ok to
* set the fd back to blocked.
*/
qemu_file_set_blocking(mis->from_src_file, true);
bioc = qio_channel_buffer_new(COLO_BUFFER_BASE_SIZE);
fb = qemu_fopen_channel_input(QIO_CHANNEL(bioc));
object_unref(OBJECT(bioc));
colo_send_message(mis->to_src_file, COLO_MESSAGE_CHECKPOINT_READY,
&local_err);
if (local_err) {
goto out;
}
while (mis->state == MIGRATION_STATUS_COLO) {
int request = 0;
colo_wait_handle_message(mis->from_src_file, &request, &local_err);
if (local_err) {
goto out;
}
assert(request);
if (failover_get_state() != FAILOVER_STATUS_NONE) {
error_report("failover request");
goto out;
}
/* FIXME: This is unnecessary for periodic checkpoint mode */
colo_send_message(mis->to_src_file, COLO_MESSAGE_CHECKPOINT_REPLY,
&local_err);
if (local_err) {
goto out;
}
colo_receive_check_message(mis->from_src_file,
COLO_MESSAGE_VMSTATE_SEND, &local_err);
if (local_err) {
goto out;
}
value = colo_receive_message_value(mis->from_src_file,
COLO_MESSAGE_VMSTATE_SIZE, &local_err);
if (local_err) {
goto out;
}
/*
* Read VM device state data into channel buffer,
* It's better to re-use the memory allocated.
* Here we need to handle the channel buffer directly.
*/
if (value > bioc->capacity) {
bioc->capacity = value;
bioc->data = g_realloc(bioc->data, bioc->capacity);
}
total_size = qemu_get_buffer(mis->from_src_file, bioc->data, value);
if (total_size != value) {
error_report("Got %" PRIu64 " VMState data, less than expected"
" %" PRIu64, total_size, value);
goto out;
}
bioc->usage = total_size;
qio_channel_io_seek(QIO_CHANNEL(bioc), 0, 0, NULL);
colo_send_message(mis->to_src_file, COLO_MESSAGE_VMSTATE_RECEIVED,
&local_err);
if (local_err) {
goto out;
}
qemu_mutex_lock_iothread();
qemu_system_reset(SHUTDOWN_CAUSE_NONE);
vmstate_loading = true;
if (qemu_loadvm_state(fb) < 0) {
error_report("COLO: loadvm failed");
qemu_mutex_unlock_iothread();
goto out;
}
vmstate_loading = false;
qemu_mutex_unlock_iothread();
if (failover_get_state() == FAILOVER_STATUS_RELAUNCH) {
failover_set_state(FAILOVER_STATUS_RELAUNCH,
FAILOVER_STATUS_NONE);
failover_request_active(NULL);
goto out;
}
colo_send_message(mis->to_src_file, COLO_MESSAGE_VMSTATE_LOADED,
&local_err);
if (local_err) {
goto out;
}
}
out:
vmstate_loading = false;
/* Throw the unreported error message after exited from loop */
if (local_err) {
error_report_err(local_err);
}
if (fb) {
qemu_fclose(fb);
}
/* Hope this not to be too long to loop here */
qemu_sem_wait(&mis->colo_incoming_sem);
qemu_sem_destroy(&mis->colo_incoming_sem);
/* Must be called after failover BH is completed */
if (mis->to_src_file) {
qemu_fclose(mis->to_src_file);
}
migration_incoming_exit_colo();
return NULL;
}
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