afs: Probe multiple fileservers simultaneously

Send probes to all the unprobed fileservers in a fileserver list on all
addresses simultaneously in an attempt to find out the fastest route whilst
not getting stuck for 20s on any server or address that we don't get a
reply from.

This alleviates the problem whereby attempting to access a new server can
take a long time because the rotation algorithm ends up rotating through
all servers and addresses until it finds one that responds.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 270 insertions, 0 deletions

diff --git a/fs/afs/fs_probe.c b/fs/afs/fs_probe.c
new file mode 100644
index 000000000000..d049cb459742
--- /dev/null
+++ b/fs/afs/fs_probe.c
@@ -0,0 +1,270 @@
+/* AFS fileserver probing
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include "afs_fs.h"
+#include "internal.h"
+#include "protocol_yfs.h"
+
+static bool afs_fs_probe_done(struct afs_server *server)
+{
+	if (!atomic_dec_and_test(&server->probe_outstanding))
+		return false;
+
+	wake_up_var(&server->probe_outstanding);
+	clear_bit_unlock(AFS_SERVER_FL_PROBING, &server->flags);
+	wake_up_bit(&server->flags, AFS_SERVER_FL_PROBING);
+	return true;
+}
+
+/*
+ * Process the result of probing a fileserver.  This is called after successful
+ * or failed delivery of an FS.GetCapabilities operation.
+ */
+void afs_fileserver_probe_result(struct afs_call *call)
+{
+	struct afs_addr_list *alist = call->alist;
+	struct afs_server *server = call->reply[0];
+	unsigned int server_index = (long)call->reply[1];
+	unsigned int index = call->addr_ix;
+	unsigned int rtt = UINT_MAX;
+	bool have_result = false;
+	u64 _rtt;
+	int ret = call->error;
+
+	_enter("%pU,%u", &server->uuid, index);
+
+	spin_lock(&server->probe_lock);
+
+	switch (ret) {
+	case 0:
+		server->probe.error = 0;
+		goto responded;
+	case -ECONNABORTED:
+		if (!server->probe.responded) {
+			server->probe.abort_code = call->abort_code;
+			server->probe.error = ret;
+		}
+		goto responded;
+	case -ENOMEM:
+	case -ENONET:
+		server->probe.local_failure = true;
+		afs_io_error(call, afs_io_error_fs_probe_fail);
+		goto out;
+	case -ECONNRESET: /* Responded, but call expired. */
+	case -ENETUNREACH:
+	case -EHOSTUNREACH:
+	case -ECONNREFUSED:
+	case -ETIMEDOUT:
+	case -ETIME:
+	default:
+		clear_bit(index, &alist->responded);
+		set_bit(index, &alist->failed);
+		if (!server->probe.responded &&
+		    (server->probe.error == 0 ||
+		     server->probe.error == -ETIMEDOUT ||
+		     server->probe.error == -ETIME))
+			server->probe.error = ret;
+		afs_io_error(call, afs_io_error_fs_probe_fail);
+		goto out;
+	}
+
+responded:
+	set_bit(index, &alist->responded);
+	clear_bit(index, &alist->failed);
+
+	if (call->service_id == YFS_FS_SERVICE) {
+		server->probe.is_yfs = true;
+		set_bit(AFS_SERVER_FL_IS_YFS, &server->flags);
+		alist->addrs[index].srx_service = call->service_id;
+	} else {
+		server->probe.not_yfs = true;
+		if (!server->probe.is_yfs) {
+			clear_bit(AFS_SERVER_FL_IS_YFS, &server->flags);
+			alist->addrs[index].srx_service = call->service_id;
+		}
+	}
+
+	/* Get the RTT and scale it to fit into a 32-bit value that represents
+	 * over a minute of time so that we can access it with one instruction
+	 * on a 32-bit system.
+	 */
+	_rtt = rxrpc_kernel_get_rtt(call->net->socket, call->rxcall);
+	_rtt /= 64;
+	rtt = (_rtt > UINT_MAX) ? UINT_MAX : _rtt;
+	if (rtt < server->probe.rtt) {
+		server->probe.rtt = rtt;
+		alist->preferred = index;
+		have_result = true;
+	}
+
+	smp_wmb(); /* Set rtt before responded. */
+	server->probe.responded = true;
+	set_bit(AFS_SERVER_FL_PROBED, &server->flags);
+out:
+	spin_unlock(&server->probe_lock);
+
+	_debug("probe [%u][%u] %pISpc rtt=%u ret=%d",
+	       server_index, index, &alist->addrs[index].transport,
+	       (unsigned int)rtt, ret);
+
+	have_result |= afs_fs_probe_done(server);
+	if (have_result) {
+		server->probe.have_result = true;
+		wake_up_var(&server->probe.have_result);
+		wake_up_all(&server->probe_wq);
+	}
+}
+
+/*
+ * Probe all of a fileserver's addresses to find out the best route and to
+ * query its capabilities.
+ */
+static int afs_do_probe_fileserver(struct afs_net *net,
+				   struct afs_server *server,
+				   struct key *key,
+				   unsigned int server_index)
+{
+	struct afs_addr_cursor ac = {
+		.index = 0,
+	};
+	int ret;
+
+	_enter("%pU", &server->uuid);
+
+	read_lock(&server->fs_lock);
+	ac.alist = rcu_dereference_protected(server->addresses,
+					     lockdep_is_held(&server->fs_lock));
+	read_unlock(&server->fs_lock);
+
+	atomic_set(&server->probe_outstanding, ac.alist->nr_addrs);
+	memset(&server->probe, 0, sizeof(server->probe));
+	server->probe.rtt = UINT_MAX;
+
+	for (ac.index = 0; ac.index < ac.alist->nr_addrs; ac.index++) {
+		ret = afs_fs_get_capabilities(net, server, &ac, key, server_index,
+					      true);
+		if (ret != -EINPROGRESS) {
+			afs_fs_probe_done(server);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Send off probes to all unprobed servers.
+ */
+int afs_probe_fileservers(struct afs_net *net, struct key *key,
+			  struct afs_server_list *list)
+{
+	struct afs_server *server;
+	int i, ret;
+
+	for (i = 0; i < list->nr_servers; i++) {
+		server = list->servers[i].server;
+		if (test_bit(AFS_SERVER_FL_PROBED, &server->flags))
+			continue;
+
+		if (!test_and_set_bit_lock(AFS_SERVER_FL_PROBING, &server->flags)) {
+			ret = afs_do_probe_fileserver(net, server, key, i);
+			if (ret)
+				return ret;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Wait for the first as-yet untried fileserver to respond.
+ */
+int afs_wait_for_fs_probes(struct afs_server_list *slist, unsigned long untried)
+{
+	struct wait_queue_entry *waits;
+	struct afs_server *server;
+	unsigned int rtt = UINT_MAX;
+	bool have_responders = false;
+	int pref = -1, i;
+
+	_enter("%u,%lx", slist->nr_servers, untried);
+
+	/* Only wait for servers that have a probe outstanding. */
+	for (i = 0; i < slist->nr_servers; i++) {
+		if (test_bit(i, &untried)) {
+			server = slist->servers[i].server;
+			if (!test_bit(AFS_SERVER_FL_PROBING, &server->flags))
+				__clear_bit(i, &untried);
+			if (server->probe.responded)
+				have_responders = true;
+		}
+	}
+	if (have_responders || !untried)
+		return 0;
+
+	waits = kmalloc(array_size(slist->nr_servers, sizeof(*waits)), GFP_KERNEL);
+	if (!waits)
+		return -ENOMEM;
+
+	for (i = 0; i < slist->nr_servers; i++) {
+		if (test_bit(i, &untried)) {
+			server = slist->servers[i].server;
+			init_waitqueue_entry(&waits[i], current);
+			add_wait_queue(&server->probe_wq, &waits[i]);
+		}
+	}
+
+	for (;;) {
+		bool still_probing = false;
+
+		set_current_state(TASK_INTERRUPTIBLE);
+		for (i = 0; i < slist->nr_servers; i++) {
+			if (test_bit(i, &untried)) {
+				server = slist->servers[i].server;
+				if (server->probe.responded)
+					goto stop;
+				if (test_bit(AFS_SERVER_FL_PROBING, &server->flags))
+					still_probing = true;
+			}
+		}
+
+		if (!still_probing || unlikely(signal_pending(current)))
+			goto stop;
+		schedule();
+	}
+
+stop:
+	set_current_state(TASK_RUNNING);
+
+	for (i = 0; i < slist->nr_servers; i++) {
+		if (test_bit(i, &untried)) {
+			server = slist->servers[i].server;
+			if (server->probe.responded &&
+			    server->probe.rtt < rtt) {
+				pref = i;
+				rtt = server->probe.rtt;
+			}
+
+			remove_wait_queue(&server->probe_wq, &waits[i]);
+		}
+	}
+
+	kfree(waits);
+
+	if (pref == -1 && signal_pending(current))
+		return -ERESTARTSYS;
+
+	if (pref >= 0)
+		slist->preferred = pref;
+	return 0;
+}