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 to be 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 <[email protected]> Signed-off-by: Sergio Lopez <[email protected]> --- nbd/server.c | 99 +++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 75 insertions(+), 24 deletions(-) diff --git a/nbd/server.c b/nbd/server.c index 86a44a9b41..33e55479d7 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -132,7 +132,7 @@ struct NBDClient { CoMutex send_lock; Coroutine *send_coroutine; - bool read_yielding; + GSList *yield_co_list; /* List of coroutines yielding on nbd_read_eof */ bool quiescing; QTAILQ_ENTRY(NBDClient) next; @@ -1367,6 +1367,7 @@ static inline int coroutine_fn nbd_read_eof(NBDClient *client, void *buffer, size_t size, Error **errp) { bool partial = false; + Coroutine *co; assert(size); while (size > 0) { @@ -1375,9 +1376,12 @@ nbd_read_eof(NBDClient *client, void *buffer, size_t size, Error **errp) len = qio_channel_readv(client->ioc, &iov, 1, errp); if (len == QIO_CHANNEL_ERR_BLOCK) { - client->read_yielding = true; + co = qemu_coroutine_self(); + + client->yield_co_list = g_slist_prepend(client->yield_co_list, co); qio_channel_yield(client->ioc, G_IO_IN); - client->read_yielding = false; + client->yield_co_list = g_slist_remove(client->yield_co_list, co); + if (client->quiescing) { return -EAGAIN; } @@ -1513,6 +1517,11 @@ 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); @@ -1530,49 +1539,75 @@ 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) +static void blk_aio_detach(void *opaque) { NBDExport *exp = opaque; NBDClient *client; + trace_nbd_blk_aio_detach(exp->name, exp->common.ctx); + 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; + } +} - 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); - } - } +static void nbd_drained_end(void *opaque) +{ + NBDExport *exp = opaque; + NBDClient *client; - if (client->send_coroutine) { - AIO_WAIT_WHILE(exp->common.ctx, client->send_coroutine != NULL); - } + QTAILQ_FOREACH(client, &exp->clients, next) { + client->quiescing = false; + nbd_client_receive_next_request(client); } } -static void blk_aio_detach(void *opaque) +static bool nbd_drained_poll(void *opaque) { NBDExport *exp = opaque; + NBDClient *client; + Coroutine *co; + GSList *entry; + GSList *coroutine_list; - trace_nbd_blk_aio_detach(exp->name, exp->common.ctx); + QTAILQ_FOREACH(client, &exp->clients, next) { + if (client->nb_requests != 0) { + /* + * Enter coroutines waiting for new requests on nbd_read_eof(), so + * we don't depend on the client to wake us up. + */ + coroutine_list = g_slist_copy(client->yield_co_list); + for (entry = coroutine_list; + entry != NULL; + entry = g_slist_next(entry)) { + co = entry->data; + qemu_aio_coroutine_enter(exp->common.ctx, co); + } + g_slist_free(coroutine_list); - aio_wait_bh_oneshot(exp->common.ctx, nbd_aio_detach_bh, exp); + return 1; + } + } - exp->common.ctx = NULL; + return 0; } static void nbd_eject_notifier(Notifier *n, void *data) @@ -1594,6 +1629,12 @@ 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 +1756,17 @@ 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 +1838,7 @@ 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++) { -- 2.26.2
