qemu/util/vhost-user-server.c
Kevin Wolf 520d8b40e8 block/export: Fix vhost-user-blk shutdown with requests in flight
The vhost-user-blk export runs requests asynchronously in their own
coroutine. When the vhost connection goes away and we want to stop the
vhost-user server, we need to wait for these coroutines to stop before
we can unmap the shared memory. Otherwise, they would still access the
unmapped memory and crash.

This introduces a refcount to VuServer which is increased when spawning
a new request coroutine and decreased before the coroutine exits. The
memory is only unmapped when the refcount reaches zero.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20220125151435.48792-1-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2022-02-01 13:49:15 +01:00

470 lines
14 KiB
C

/*
* Sharing QEMU devices via vhost-user protocol
*
* Copyright (c) Coiby Xu <coiby.xu@gmail.com>.
* Copyright (c) 2020 Red Hat, Inc.
*
* 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 "qemu/main-loop.h"
#include "qemu/vhost-user-server.h"
#include "block/aio-wait.h"
/*
* Theory of operation:
*
* VuServer is started and stopped by vhost_user_server_start() and
* vhost_user_server_stop() from the main loop thread. Starting the server
* opens a vhost-user UNIX domain socket and listens for incoming connections.
* Only one connection is allowed at a time.
*
* The connection is handled by the vu_client_trip() coroutine in the
* VuServer->ctx AioContext. The coroutine consists of a vu_dispatch() loop
* where libvhost-user calls vu_message_read() to receive the next vhost-user
* protocol messages over the UNIX domain socket.
*
* When virtqueues are set up libvhost-user calls set_watch() to monitor kick
* fds. These fds are also handled in the VuServer->ctx AioContext.
*
* Both vu_client_trip() and kick fd monitoring can be stopped by shutting down
* the socket connection. Shutting down the socket connection causes
* vu_message_read() to fail since no more data can be received from the socket.
* After vu_dispatch() fails, vu_client_trip() calls vu_deinit() to stop
* libvhost-user before terminating the coroutine. vu_deinit() calls
* remove_watch() to stop monitoring kick fds and this stops virtqueue
* processing.
*
* When vu_client_trip() has finished cleaning up it schedules a BH in the main
* loop thread to accept the next client connection.
*
* When libvhost-user detects an error it calls panic_cb() and sets the
* dev->broken flag. Both vu_client_trip() and kick fd processing stop when
* the dev->broken flag is set.
*
* It is possible to switch AioContexts using
* vhost_user_server_detach_aio_context() and
* vhost_user_server_attach_aio_context(). They stop monitoring fds in the old
* AioContext and resume monitoring in the new AioContext. The vu_client_trip()
* coroutine remains in a yielded state during the switch. This is made
* possible by QIOChannel's support for spurious coroutine re-entry in
* qio_channel_yield(). The coroutine will restart I/O when re-entered from the
* new AioContext.
*/
static void vmsg_close_fds(VhostUserMsg *vmsg)
{
int i;
for (i = 0; i < vmsg->fd_num; i++) {
close(vmsg->fds[i]);
}
}
static void vmsg_unblock_fds(VhostUserMsg *vmsg)
{
int i;
for (i = 0; i < vmsg->fd_num; i++) {
qemu_set_nonblock(vmsg->fds[i]);
}
}
static void panic_cb(VuDev *vu_dev, const char *buf)
{
error_report("vu_panic: %s", buf);
}
void vhost_user_server_ref(VuServer *server)
{
assert(!server->wait_idle);
server->refcount++;
}
void vhost_user_server_unref(VuServer *server)
{
server->refcount--;
if (server->wait_idle && !server->refcount) {
aio_co_wake(server->co_trip);
}
}
static bool coroutine_fn
vu_message_read(VuDev *vu_dev, int conn_fd, VhostUserMsg *vmsg)
{
struct iovec iov = {
.iov_base = (char *)vmsg,
.iov_len = VHOST_USER_HDR_SIZE,
};
int rc, read_bytes = 0;
Error *local_err = NULL;
const size_t max_fds = G_N_ELEMENTS(vmsg->fds);
VuServer *server = container_of(vu_dev, VuServer, vu_dev);
QIOChannel *ioc = server->ioc;
vmsg->fd_num = 0;
if (!ioc) {
error_report_err(local_err);
goto fail;
}
assert(qemu_in_coroutine());
do {
size_t nfds = 0;
int *fds = NULL;
/*
* qio_channel_readv_full may have short reads, keeping calling it
* until getting VHOST_USER_HDR_SIZE or 0 bytes in total
*/
rc = qio_channel_readv_full(ioc, &iov, 1, &fds, &nfds, &local_err);
if (rc < 0) {
if (rc == QIO_CHANNEL_ERR_BLOCK) {
assert(local_err == NULL);
qio_channel_yield(ioc, G_IO_IN);
continue;
} else {
error_report_err(local_err);
goto fail;
}
}
if (nfds > 0) {
if (vmsg->fd_num + nfds > max_fds) {
error_report("A maximum of %zu fds are allowed, "
"however got %zu fds now",
max_fds, vmsg->fd_num + nfds);
g_free(fds);
goto fail;
}
memcpy(vmsg->fds + vmsg->fd_num, fds, nfds * sizeof(vmsg->fds[0]));
vmsg->fd_num += nfds;
g_free(fds);
}
if (rc == 0) { /* socket closed */
goto fail;
}
iov.iov_base += rc;
iov.iov_len -= rc;
read_bytes += rc;
} while (read_bytes != VHOST_USER_HDR_SIZE);
/* qio_channel_readv_full will make socket fds blocking, unblock them */
vmsg_unblock_fds(vmsg);
if (vmsg->size > sizeof(vmsg->payload)) {
error_report("Error: too big message request: %d, "
"size: vmsg->size: %u, "
"while sizeof(vmsg->payload) = %zu",
vmsg->request, vmsg->size, sizeof(vmsg->payload));
goto fail;
}
struct iovec iov_payload = {
.iov_base = (char *)&vmsg->payload,
.iov_len = vmsg->size,
};
if (vmsg->size) {
rc = qio_channel_readv_all_eof(ioc, &iov_payload, 1, &local_err);
if (rc != 1) {
if (local_err) {
error_report_err(local_err);
}
goto fail;
}
}
return true;
fail:
vmsg_close_fds(vmsg);
return false;
}
static coroutine_fn void vu_client_trip(void *opaque)
{
VuServer *server = opaque;
VuDev *vu_dev = &server->vu_dev;
while (!vu_dev->broken && vu_dispatch(vu_dev)) {
/* Keep running */
}
if (server->refcount) {
/* Wait for requests to complete before we can unmap the memory */
server->wait_idle = true;
qemu_coroutine_yield();
server->wait_idle = false;
}
assert(server->refcount == 0);
vu_deinit(vu_dev);
/* vu_deinit() should have called remove_watch() */
assert(QTAILQ_EMPTY(&server->vu_fd_watches));
object_unref(OBJECT(server->sioc));
server->sioc = NULL;
object_unref(OBJECT(server->ioc));
server->ioc = NULL;
server->co_trip = NULL;
if (server->restart_listener_bh) {
qemu_bh_schedule(server->restart_listener_bh);
}
aio_wait_kick();
}
/*
* a wrapper for vu_kick_cb
*
* since aio_dispatch can only pass one user data pointer to the
* callback function, pack VuDev and pvt into a struct. Then unpack it
* and pass them to vu_kick_cb
*/
static void kick_handler(void *opaque)
{
VuFdWatch *vu_fd_watch = opaque;
VuDev *vu_dev = vu_fd_watch->vu_dev;
vu_fd_watch->cb(vu_dev, 0, vu_fd_watch->pvt);
/* Stop vu_client_trip() if an error occurred in vu_fd_watch->cb() */
if (vu_dev->broken) {
VuServer *server = container_of(vu_dev, VuServer, vu_dev);
qio_channel_shutdown(server->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
}
}
static VuFdWatch *find_vu_fd_watch(VuServer *server, int fd)
{
VuFdWatch *vu_fd_watch, *next;
QTAILQ_FOREACH_SAFE(vu_fd_watch, &server->vu_fd_watches, next, next) {
if (vu_fd_watch->fd == fd) {
return vu_fd_watch;
}
}
return NULL;
}
static void
set_watch(VuDev *vu_dev, int fd, int vu_evt,
vu_watch_cb cb, void *pvt)
{
VuServer *server = container_of(vu_dev, VuServer, vu_dev);
g_assert(vu_dev);
g_assert(fd >= 0);
g_assert(cb);
VuFdWatch *vu_fd_watch = find_vu_fd_watch(server, fd);
if (!vu_fd_watch) {
VuFdWatch *vu_fd_watch = g_new0(VuFdWatch, 1);
QTAILQ_INSERT_TAIL(&server->vu_fd_watches, vu_fd_watch, next);
vu_fd_watch->fd = fd;
vu_fd_watch->cb = cb;
qemu_set_nonblock(fd);
aio_set_fd_handler(server->ioc->ctx, fd, true, kick_handler,
NULL, NULL, NULL, vu_fd_watch);
vu_fd_watch->vu_dev = vu_dev;
vu_fd_watch->pvt = pvt;
}
}
static void remove_watch(VuDev *vu_dev, int fd)
{
VuServer *server;
g_assert(vu_dev);
g_assert(fd >= 0);
server = container_of(vu_dev, VuServer, vu_dev);
VuFdWatch *vu_fd_watch = find_vu_fd_watch(server, fd);
if (!vu_fd_watch) {
return;
}
aio_set_fd_handler(server->ioc->ctx, fd, true,
NULL, NULL, NULL, NULL, NULL);
QTAILQ_REMOVE(&server->vu_fd_watches, vu_fd_watch, next);
g_free(vu_fd_watch);
}
static void vu_accept(QIONetListener *listener, QIOChannelSocket *sioc,
gpointer opaque)
{
VuServer *server = opaque;
if (server->sioc) {
warn_report("Only one vhost-user client is allowed to "
"connect the server one time");
return;
}
if (!vu_init(&server->vu_dev, server->max_queues, sioc->fd, panic_cb,
vu_message_read, set_watch, remove_watch, server->vu_iface)) {
error_report("Failed to initialize libvhost-user");
return;
}
/*
* Unset the callback function for network listener to make another
* vhost-user client keeping waiting until this client disconnects
*/
qio_net_listener_set_client_func(server->listener,
NULL,
NULL,
NULL);
server->sioc = sioc;
/*
* Increase the object reference, so sioc will not freed by
* qio_net_listener_channel_func which will call object_unref(OBJECT(sioc))
*/
object_ref(OBJECT(server->sioc));
qio_channel_set_name(QIO_CHANNEL(sioc), "vhost-user client");
server->ioc = QIO_CHANNEL(sioc);
object_ref(OBJECT(server->ioc));
/* TODO vu_message_write() spins if non-blocking! */
qio_channel_set_blocking(server->ioc, false, NULL);
server->co_trip = qemu_coroutine_create(vu_client_trip, server);
aio_context_acquire(server->ctx);
vhost_user_server_attach_aio_context(server, server->ctx);
aio_context_release(server->ctx);
}
void vhost_user_server_stop(VuServer *server)
{
aio_context_acquire(server->ctx);
qemu_bh_delete(server->restart_listener_bh);
server->restart_listener_bh = NULL;
if (server->sioc) {
VuFdWatch *vu_fd_watch;
QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
aio_set_fd_handler(server->ctx, vu_fd_watch->fd, true,
NULL, NULL, NULL, NULL, vu_fd_watch);
}
qio_channel_shutdown(server->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
AIO_WAIT_WHILE(server->ctx, server->co_trip);
}
aio_context_release(server->ctx);
if (server->listener) {
qio_net_listener_disconnect(server->listener);
object_unref(OBJECT(server->listener));
}
}
/*
* Allow the next client to connect to the server. Called from a BH in the main
* loop.
*/
static void restart_listener_bh(void *opaque)
{
VuServer *server = opaque;
qio_net_listener_set_client_func(server->listener, vu_accept, server,
NULL);
}
/* Called with ctx acquired */
void vhost_user_server_attach_aio_context(VuServer *server, AioContext *ctx)
{
VuFdWatch *vu_fd_watch;
server->ctx = ctx;
if (!server->sioc) {
return;
}
qio_channel_attach_aio_context(server->ioc, ctx);
QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
aio_set_fd_handler(ctx, vu_fd_watch->fd, true, kick_handler, NULL,
NULL, NULL, vu_fd_watch);
}
aio_co_schedule(ctx, server->co_trip);
}
/* Called with server->ctx acquired */
void vhost_user_server_detach_aio_context(VuServer *server)
{
if (server->sioc) {
VuFdWatch *vu_fd_watch;
QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
aio_set_fd_handler(server->ctx, vu_fd_watch->fd, true,
NULL, NULL, NULL, NULL, vu_fd_watch);
}
qio_channel_detach_aio_context(server->ioc);
}
server->ctx = NULL;
}
bool vhost_user_server_start(VuServer *server,
SocketAddress *socket_addr,
AioContext *ctx,
uint16_t max_queues,
const VuDevIface *vu_iface,
Error **errp)
{
QEMUBH *bh;
QIONetListener *listener;
if (socket_addr->type != SOCKET_ADDRESS_TYPE_UNIX &&
socket_addr->type != SOCKET_ADDRESS_TYPE_FD) {
error_setg(errp, "Only socket address types 'unix' and 'fd' are supported");
return false;
}
listener = qio_net_listener_new();
if (qio_net_listener_open_sync(listener, socket_addr, 1,
errp) < 0) {
object_unref(OBJECT(listener));
return false;
}
bh = qemu_bh_new(restart_listener_bh, server);
/* zero out unspecified fields */
*server = (VuServer) {
.listener = listener,
.restart_listener_bh = bh,
.vu_iface = vu_iface,
.max_queues = max_queues,
.ctx = ctx,
};
qio_net_listener_set_name(server->listener, "vhost-user-backend-listener");
qio_net_listener_set_client_func(server->listener,
vu_accept,
server,
NULL);
QTAILQ_INIT(&server->vu_fd_watches);
return true;
}