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nbd/server: Use drained block ops to quiesce the server 

Before switching between AioContexts we need to make sure that we're
fully quiesced ("nb_requests == 0" for every client) when entering the
drained section.

To do this, we set "quiescing = true" for every client on
".drained_begin" to prevent new coroutines from being created, and
check if "nb_requests == 0" on ".drained_poll". Finally, once we're
exiting the drained section, on ".drained_end" we set "quiescing =
false" and call "nbd_client_receive_next_request()" to resume the
processing of new requests.

With these changes, "blk_aio_attach()" and "blk_aio_detach()" can be
reverted to be as simple as they were before f148ae7d36.

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1960137
Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Sergio Lopez <slp@redhat.com>
Message-Id: <20210602060552.17433-3-slp@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Sergio Lopez 2021-06-02 08:05:52 +02:00 committed by Kevin Wolf
parent 095cc4d0f6
commit fd6afc501a
1 changed files with 70 additions and 30 deletions
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100
nbd/server.c
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@ -1513,6 +1513,11 @@ static void nbd_request_put(NBDRequestData *req)
g_free(req);
client->nb_requests--;
if (client->quiescing && client->nb_requests == 0) {
aio_wait_kick();
}
nbd_client_receive_next_request(client);
nbd_client_put(client);
@ -1530,51 +1535,70 @@ static void blk_aio_attached(AioContext *ctx, void *opaque)
QTAILQ_FOREACH(client, &exp->clients, next) {
qio_channel_attach_aio_context(client->ioc, ctx);
assert(client->nb_requests == 0);
assert(client->recv_coroutine == NULL);
assert(client->send_coroutine == NULL);
if (client->quiescing) {
client->quiescing = false;
nbd_client_receive_next_request(client);
}
}
}
static void nbd_aio_detach_bh(void *opaque)
{
NBDExport *exp = opaque;
NBDClient *client;
QTAILQ_FOREACH(client, &exp->clients, next) {
qio_channel_detach_aio_context(client->ioc);
client->quiescing = true;
if (client->recv_coroutine) {
if (client->read_yielding) {
qemu_aio_coroutine_enter(exp->common.ctx,
client->recv_coroutine);
} else {
AIO_WAIT_WHILE(exp->common.ctx, client->recv_coroutine != NULL);
}
}
if (client->send_coroutine) {
AIO_WAIT_WHILE(exp->common.ctx, client->send_coroutine != NULL);
}
}
}
static void blk_aio_detach(void *opaque)
{
NBDExport *exp = opaque;
NBDClient *client;
trace_nbd_blk_aio_detach(exp->name, exp->common.ctx);
aio_wait_bh_oneshot(exp->common.ctx, nbd_aio_detach_bh, exp);
QTAILQ_FOREACH(client, &exp->clients, next) {
qio_channel_detach_aio_context(client->ioc);
}
exp->common.ctx = NULL;
}
static void nbd_drained_begin(void *opaque)
{
NBDExport *exp = opaque;
NBDClient *client;
QTAILQ_FOREACH(client, &exp->clients, next) {
client->quiescing = true;
}
}
static void nbd_drained_end(void *opaque)
{
NBDExport *exp = opaque;
NBDClient *client;
QTAILQ_FOREACH(client, &exp->clients, next) {
client->quiescing = false;
nbd_client_receive_next_request(client);
}
}
static bool nbd_drained_poll(void *opaque)
{
NBDExport *exp = opaque;
NBDClient *client;
QTAILQ_FOREACH(client, &exp->clients, next) {
if (client->nb_requests != 0) {
/*
* If there's a coroutine waiting for a request on nbd_read_eof()
* enter it here so we don't depend on the client to wake it up.
*/
if (client->recv_coroutine != NULL && client->read_yielding) {
qemu_aio_coroutine_enter(exp->common.ctx,
client->recv_coroutine);
}
return true;
}
}
return false;
}
static void nbd_eject_notifier(Notifier *n, void *data)
{
NBDExport *exp = container_of(n, NBDExport, eject_notifier);
@ -1594,6 +1618,12 @@ void nbd_export_set_on_eject_blk(BlockExport *exp, BlockBackend *blk)
blk_add_remove_bs_notifier(blk, &nbd_exp->eject_notifier);
}
static const BlockDevOps nbd_block_ops = {
.drained_begin = nbd_drained_begin,
.drained_end = nbd_drained_end,
.drained_poll = nbd_drained_poll,
};
static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args,
Error **errp)
{
@ -1715,8 +1745,17 @@ static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args,
exp->allocation_depth = arg->allocation_depth;
/*
* We need to inhibit request queuing in the block layer to ensure we can
* be properly quiesced when entering a drained section, as our coroutines
* servicing pending requests might enter blk_pread().
*/
blk_set_disable_request_queuing(blk, true);
blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp);
blk_set_dev_ops(blk, &nbd_block_ops, exp);
QTAILQ_INSERT_TAIL(&exports, exp, next);
return 0;
@ -1788,6 +1827,7 @@ static void nbd_export_delete(BlockExport *blk_exp)
}
blk_remove_aio_context_notifier(exp->common.blk, blk_aio_attached,
blk_aio_detach, exp);
blk_set_disable_request_queuing(exp->common.blk, false);
}
for (i = 0; i < exp->nr_export_bitmaps; i++) {