12 files changed, 844 insertions, 561 deletions

diff --git a/fs/afs/Makefile b/fs/afs/Makefile
index 641148208e90..849383986d3b 100644
--- a/fs/afs/Makefile
+++ b/fs/afs/Makefile
@@ -7,6 +7,7 @@ afs-cache-$(CONFIG_AFS_FSCACHE) := cache.o
 
 kafs-objs := \
 	$(afs-cache-y) \
+	addr_list.o \
 	callback.o \
 	cell.o \
 	cmservice.o \
diff --git a/fs/afs/addr_list.c b/fs/afs/addr_list.c
new file mode 100644
index 000000000000..ecb9c72aebd2
--- /dev/null
+++ b/fs/afs/addr_list.c
@@ -0,0 +1,308 @@
+/* Server address list management
+ *
+ * Copyright (C) 2017 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/slab.h>
+#include <linux/ctype.h>
+#include <linux/dns_resolver.h>
+#include <linux/inet.h>
+#include <keys/rxrpc-type.h>
+#include "internal.h"
+#include "afs_fs.h"
+
+#define AFS_MAX_ADDRESSES						\
+	((unsigned int)((PAGE_SIZE - sizeof(struct afs_addr_list)) /	\
+			sizeof(struct sockaddr_rxrpc)))
+
+/*
+ * Release an address list.
+ */
+void afs_put_addrlist(struct afs_addr_list *alist)
+{
+	if (alist && refcount_dec_and_test(&alist->usage))
+		call_rcu(&alist->rcu, (rcu_callback_t)kfree);
+}
+
+/*
+ * Allocate an address list.
+ */
+struct afs_addr_list *afs_alloc_addrlist(unsigned int nr,
+					 unsigned short service,
+					 unsigned short port)
+{
+	struct afs_addr_list *alist;
+	unsigned int i;
+
+	_enter("%u,%u,%u", nr, service, port);
+
+	alist = kzalloc(sizeof(*alist) + sizeof(alist->addrs[0]) * nr,
+			GFP_KERNEL);
+	if (!alist)
+		return NULL;
+
+	refcount_set(&alist->usage, 1);
+
+	for (i = 0; i < nr; i++) {
+		struct sockaddr_rxrpc *srx = &alist->addrs[i];
+		srx->srx_family			= AF_RXRPC;
+		srx->srx_service		= service;
+		srx->transport_type		= SOCK_DGRAM;
+		srx->transport_len		= sizeof(srx->transport.sin6);
+		srx->transport.sin6.sin6_family	= AF_INET6;
+		srx->transport.sin6.sin6_port	= htons(port);
+	}
+
+	return alist;
+}
+
+/*
+ * Parse a text string consisting of delimited addresses.
+ */
+struct afs_addr_list *afs_parse_text_addrs(const char *text, size_t len,
+					   char delim,
+					   unsigned short service,
+					   unsigned short port)
+{
+	struct afs_addr_list *alist;
+	const char *p, *end = text + len;
+	unsigned int nr = 0;
+
+	_enter("%*.*s,%c", (int)len, (int)len, text, delim);
+
+	if (!len)
+		return ERR_PTR(-EDESTADDRREQ);
+
+	if (delim == ':' && (memchr(text, ',', len) || !memchr(text, '.', len)))
+		delim = ',';
+
+	/* Count the addresses */
+	p = text;
+	do {
+		if (!*p)
+			return ERR_PTR(-EINVAL);
+		if (*p == delim)
+			continue;
+		nr++;
+		if (*p == '[') {
+			p++;
+			if (p == end)
+				return ERR_PTR(-EINVAL);
+			p = memchr(p, ']', end - p);
+			if (!p)
+				return ERR_PTR(-EINVAL);
+			p++;
+			if (p >= end)
+				break;
+		}
+
+		p = memchr(p, delim, end - p);
+		if (!p)
+			break;
+		p++;
+	} while (p < end);
+
+	_debug("%u/%u addresses", nr, AFS_MAX_ADDRESSES);
+	if (nr > AFS_MAX_ADDRESSES)
+		nr = AFS_MAX_ADDRESSES;
+
+	alist = afs_alloc_addrlist(nr, service, port);
+	if (!alist)
+		return ERR_PTR(-ENOMEM);
+
+	/* Extract the addresses */
+	p = text;
+	do {
+		struct sockaddr_rxrpc *srx = &alist->addrs[alist->nr_addrs];
+		char tdelim = delim;
+
+		if (*p == delim) {
+			p++;
+			continue;
+		}
+
+		if (*p == '[') {
+			p++;
+			tdelim = ']';
+		}
+
+		if (in4_pton(p, end - p,
+			     (u8 *)&srx->transport.sin6.sin6_addr.s6_addr32[3],
+			     tdelim, &p)) {
+			srx->transport.sin6.sin6_addr.s6_addr32[0] = 0;
+			srx->transport.sin6.sin6_addr.s6_addr32[1] = 0;
+			srx->transport.sin6.sin6_addr.s6_addr32[2] = htonl(0xffff);
+		} else if (in6_pton(p, end - p,
+				    srx->transport.sin6.sin6_addr.s6_addr,
+				    tdelim, &p)) {
+			/* Nothing to do */
+		} else {
+			goto bad_address;
+		}
+
+		if (tdelim == ']') {
+			if (p == end || *p != ']')
+				goto bad_address;
+			p++;
+		}
+
+		if (p < end) {
+			if (*p == '+') {
+				/* Port number specification "+1234" */
+				unsigned int xport = 0;
+				p++;
+				if (p >= end || !isdigit(*p))
+					goto bad_address;
+				do {
+					xport *= 10;
+					xport += *p - '0';
+					if (xport > 65535)
+						goto bad_address;
+					p++;
+				} while (p < end && isdigit(*p));
+				srx->transport.sin6.sin6_port = htons(xport);
+			} else if (*p == delim) {
+				p++;
+			} else {
+				goto bad_address;
+			}
+		}
+
+		alist->nr_addrs++;
+	} while (p < end && alist->nr_addrs < AFS_MAX_ADDRESSES);
+
+	_leave(" = [nr %u]", alist->nr_addrs);
+	return alist;
+
+bad_address:
+	kfree(alist);
+	return ERR_PTR(-EINVAL);
+}
+
+/*
+ * Compare old and new address lists to see if there's been any change.
+ * - How to do this in better than O(Nlog(N)) time?
+ *   - We don't really want to sort the address list, but would rather take the
+ *     list as we got it so as not to undo record rotation by the DNS server.
+ */
+#if 0
+static int afs_cmp_addr_list(const struct afs_addr_list *a1,
+			     const struct afs_addr_list *a2)
+{
+}
+#endif
+
+/*
+ * Perform a DNS query for VL servers and build a up an address list.
+ */
+struct afs_addr_list *afs_dns_query(struct afs_cell *cell, time64_t *_expiry)
+{
+	struct afs_addr_list *alist;
+	char *vllist = NULL;
+	int ret;
+
+	_enter("%s", cell->name);
+
+	ret = dns_query("afsdb", cell->name, cell->name_len,
+			"ipv4", &vllist, _expiry);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	alist = afs_parse_text_addrs(vllist, strlen(vllist), ',',
+				     VL_SERVICE, AFS_VL_PORT);
+	if (IS_ERR(alist)) {
+		kfree(vllist);
+		if (alist != ERR_PTR(-ENOMEM))
+			pr_err("Failed to parse DNS data\n");
+		return alist;
+	}
+
+	kfree(vllist);
+	return alist;
+}
+
+/*
+ * Get an address to try.
+ */
+bool afs_iterate_addresses(struct afs_addr_cursor *ac)
+{
+	_enter("%hu+%hd", ac->start, (short)ac->index);
+
+	if (!ac->alist)
+		return false;
+
+	if (ac->begun) {
+		ac->index++;
+		if (ac->index == ac->alist->nr_addrs)
+			ac->index = 0;
+
+		if (ac->index == ac->start) {
+			ac->error = -EDESTADDRREQ;
+			return false;
+		}
+	}
+
+	ac->begun = true;
+	ac->responded = false;
+	ac->addr = &ac->alist->addrs[ac->index];
+	return true;
+}
+
+/*
+ * Release an address list cursor.
+ */
+int afs_end_cursor(struct afs_addr_cursor *ac)
+{
+	if (ac->responded && ac->index != ac->start)
+		WRITE_ONCE(ac->alist->index, ac->index);
+
+	afs_put_addrlist(ac->alist);
+	ac->alist = NULL;
+	return ac->error;
+}
+
+/*
+ * Set the address cursor for iterating over VL servers.
+ */
+int afs_set_vl_cursor(struct afs_addr_cursor *ac, struct afs_cell *cell)
+{
+	struct afs_addr_list *alist;
+	int ret;
+
+	if (!rcu_access_pointer(cell->vl_addrs)) {
+		ret = wait_on_bit(&cell->flags, AFS_CELL_FL_NO_LOOKUP_YET,
+				  TASK_INTERRUPTIBLE);
+		if (ret < 0)
+			return ret;
+
+		if (!rcu_access_pointer(cell->vl_addrs) &&
+		    ktime_get_real_seconds() < cell->dns_expiry)
+			return cell->error;
+	}
+
+	read_lock(&cell->vl_addrs_lock);
+	alist = rcu_dereference_protected(cell->vl_addrs,
+					  lockdep_is_held(&cell->vl_addrs_lock));
+	if (alist->nr_addrs > 0)
+		afs_get_addrlist(alist);
+	else
+		alist = NULL;
+	read_unlock(&cell->vl_addrs_lock);
+
+	if (!alist)
+		return -EDESTADDRREQ;
+
+	ac->alist = alist;
+	ac->addr = NULL;
+	ac->start = READ_ONCE(alist->index);
+	ac->index = ac->start;
+	ac->error = 0;
+	ac->begun = false;
+	return 0;
+}
diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index e83103e8a6fb..a0e08d3a108c 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -9,7 +9,6 @@
  * 2 of the License, or (at your option) any later version.
  */
 
-#include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/key.h>
 #include <linux/ctype.h>
@@ -152,68 +151,33 @@ static struct afs_cell *afs_alloc_cell(struct afs_net *net,
 	init_rwsem(&cell->vl_sem);
 	INIT_LIST_HEAD(&cell->vl_list);
 	spin_lock_init(&cell->vl_lock);
-	seqlock_init(&cell->vl_addrs_lock);
-	cell->flags = (1 << AFS_CELL_FL_NOT_READY);
-
-	for (i = 0; i < AFS_CELL_MAX_ADDRS; i++) {
-		struct sockaddr_rxrpc *srx = &cell->vl_addrs[i];
-		srx->srx_family			= AF_RXRPC;
-		srx->srx_service		= VL_SERVICE;
-		srx->transport_type		= SOCK_DGRAM;
-		srx->transport.sin6.sin6_family	= AF_INET6;
-		srx->transport.sin6.sin6_port	= htons(AFS_VL_PORT);
-	}
+	cell->flags = ((1 << AFS_CELL_FL_NOT_READY) |
+		       (1 << AFS_CELL_FL_NO_LOOKUP_YET));
+	rwlock_init(&cell->vl_addrs_lock);
 
 	/* Fill in the VL server list if we were given a list of addresses to
 	 * use.
 	 */
 	if (vllist) {
-		char delim = ':';
-
-		if (strchr(vllist, ',') || !strchr(vllist, '.'))
-			delim = ',';
-
-		do {
-			struct sockaddr_rxrpc *srx = &cell->vl_addrs[cell->vl_naddrs];
-
-			if (in4_pton(vllist, -1,
-				     (u8 *)&srx->transport.sin6.sin6_addr.s6_addr32[3],
-				     delim, &vllist)) {
-				srx->transport_len = sizeof(struct sockaddr_in6);
-				srx->transport.sin6.sin6_addr.s6_addr32[0] = 0;
-				srx->transport.sin6.sin6_addr.s6_addr32[1] = 0;
-				srx->transport.sin6.sin6_addr.s6_addr32[2] = htonl(0xffff);
-			} else if (in6_pton(vllist, -1,
-					    srx->transport.sin6.sin6_addr.s6_addr,
-					    delim, &vllist)) {
-				srx->transport_len = sizeof(struct sockaddr_in6);
-				srx->transport.sin6.sin6_family	= AF_INET6;
-			} else {
-				goto bad_address;
-			}
+		struct afs_addr_list *alist;
 
-			cell->vl_naddrs++;
-			if (!*vllist)
-				break;
-			vllist++;
-
-		} while (cell->vl_naddrs < AFS_CELL_MAX_ADDRS && vllist);
+		alist = afs_parse_text_addrs(vllist, strlen(vllist), ':',
+					     VL_SERVICE, AFS_VL_PORT);
+		if (IS_ERR(alist)) {
+			ret = PTR_ERR(alist);
+			goto parse_failed;
+		}
 
-		/* Disable DNS refresh for manually-specified cells */
+		rcu_assign_pointer(cell->vl_addrs, alist);
 		cell->dns_expiry = TIME64_MAX;
-	} else {
-		/* We're going to need to 'refresh' this cell's VL server list
-		 * from the DNS before we can use it.
-		 */
-		cell->dns_expiry = S64_MIN;
 	}
 
 	_leave(" = %p", cell);
 	return cell;
 
-bad_address:
-	printk(KERN_ERR "kAFS: bad VL server IP address\n");
-	ret = -EINVAL;
+parse_failed:
+	if (ret == -EINVAL)
+		printk(KERN_ERR "kAFS: bad VL server IP address\n");
 	kfree(cell);
 	_leave(" = %d", ret);
 	return ERR_PTR(ret);
@@ -325,7 +289,6 @@ cell_already_exists:
 	if (excl) {
 		ret = -EEXIST;
 	} else {
-		ASSERTCMP(atomic_read(&cursor->usage), >=, 1);
 		afs_get_cell(cursor);
 		ret = 0;
 	}
@@ -333,8 +296,10 @@ cell_already_exists:
 	kfree(candidate);
 	if (ret == 0)
 		goto wait_for_cell;
+	goto error_noput;
 error:
 	afs_put_cell(net, cell);
+error_noput:
 	_leave(" = %d [error]", ret);
 	return ERR_PTR(ret);
 }
@@ -396,78 +361,50 @@ int afs_cell_init(struct afs_net *net, const char *rootcell)
  */
 static void afs_update_cell(struct afs_cell *cell)
 {
+	struct afs_addr_list *alist, *old;
 	time64_t now, expiry;
-	char *vllist = NULL;
-	int ret;
 
 	_enter("%s", cell->name);
 
-	ret = dns_query("afsdb", cell->name, cell->name_len,
-			"ipv4", &vllist, &expiry);
-	_debug("query %d", ret);
-	switch (ret) {
-	case 0 ... INT_MAX:
-		clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
-		clear_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
-		goto parse_dns_data;
+	alist = afs_dns_query(cell, &expiry);
+	if (IS_ERR(alist)) {
+		switch (PTR_ERR(alist)) {
+		case -ENODATA:
+			/* The DNS said that the cell does not exist */
+			set_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
+			clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
+			cell->dns_expiry = ktime_get_real_seconds() + 61;
+			break;
 
-	case -ENODATA:
-		clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
-		set_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
-		cell->dns_expiry = ktime_get_real_seconds() + 61;
-		cell->error = -EDESTADDRREQ;
-		goto out;
+		case -EAGAIN:
+		case -ECONNREFUSED:
+		default:
+			set_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
+			cell->dns_expiry = ktime_get_real_seconds() + 10;
+			break;
+		}
 
-	case -EAGAIN:
-	case -ECONNREFUSED:
-	default:
-		/* Unable to query DNS. */
-		set_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
-		cell->dns_expiry = ktime_get_real_seconds() + 10;
 		cell->error = -EDESTADDRREQ;
-		goto out;
-	}
-
-parse_dns_data:
-	write_seqlock(&cell->vl_addrs_lock);
-
-	ret = -EINVAL;
-	do {
-		struct sockaddr_rxrpc *srx = &cell->vl_addrs[cell->vl_naddrs];
-
-		if (in4_pton(vllist, -1,
-			     (u8 *)&srx->transport.sin6.sin6_addr.s6_addr32[3],
-			     ',', (const char **)&vllist)) {
-			srx->transport_len = sizeof(struct sockaddr_in6);
-			srx->transport.sin6.sin6_addr.s6_addr32[0] = 0;
-			srx->transport.sin6.sin6_addr.s6_addr32[1] = 0;
-			srx->transport.sin6.sin6_addr.s6_addr32[2] = htonl(0xffff);
-		} else if (in6_pton(vllist, -1,
-				    srx->transport.sin6.sin6_addr.s6_addr,
-				    ',', (const char **)&vllist)) {
-			srx->transport_len = sizeof(struct sockaddr_in6);
-			srx->transport.sin6.sin6_family	= AF_INET6;
-		} else {
-			goto bad_address;
-		}
+	} else {
+		clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
+		clear_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
 
-		cell->vl_naddrs++;
-		if (!*vllist)
-			break;
-		vllist++;
+		/* Exclusion on changing vl_addrs is achieved by a
+		 * non-reentrant work item.
+		 */
+		old = rcu_dereference_protected(cell->vl_addrs, true);
+		rcu_assign_pointer(cell->vl_addrs, alist);
+		cell->dns_expiry = expiry;
 
-	} while (cell->vl_naddrs < AFS_CELL_MAX_ADDRS);
+		if (old)
+			afs_put_addrlist(old);
+	}
 
-	if (cell->vl_naddrs < AFS_CELL_MAX_ADDRS)
-		memset(cell->vl_addrs + cell->vl_naddrs, 0,
-		       (AFS_CELL_MAX_ADDRS - cell->vl_naddrs) * sizeof(cell->vl_addrs[0]));
+	if (test_and_clear_bit(AFS_CELL_FL_NO_LOOKUP_YET, &cell->flags))
+		wake_up_bit(&cell->flags, AFS_CELL_FL_NO_LOOKUP_YET);
 
 	now = ktime_get_real_seconds();
-	cell->dns_expiry = expiry;
-	afs_set_cell_timer(cell->net, expiry - now);
-bad_address:
-	write_sequnlock(&cell->vl_addrs_lock);
-out:
+	afs_set_cell_timer(cell->net, cell->dns_expiry - now);
 	_leave("");
 }
 
@@ -482,6 +419,7 @@ static void afs_cell_destroy(struct rcu_head *rcu)
 
 	ASSERTCMP(atomic_read(&cell->usage), ==, 0);
 
+	afs_put_addrlist(cell->vl_addrs);
 	key_put(cell->anonymous_key);
 	kfree(cell);
 
@@ -515,6 +453,15 @@ void afs_cells_timer(struct timer_list *timer)
 }
 
 /*
+ * Get a reference on a cell record.
+ */
+struct afs_cell *afs_get_cell(struct afs_cell *cell)
+{
+	atomic_inc(&cell->usage);
+	return cell;
+}
+
+/*
  * Drop a reference on a cell record.
  */
 void afs_put_cell(struct afs_net *net, struct afs_cell *cell)
diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
index 680c02d510f7..6614d0a78daa 100644
--- a/fs/afs/fsclient.c
+++ b/fs/afs/fsclient.c
@@ -297,7 +297,7 @@ static const struct afs_call_type afs_RXFSFetchStatus = {
 /*
  * fetch the status information for a file
  */
-int afs_fs_fetch_file_status(struct afs_server *server,
+int afs_fs_fetch_file_status(struct afs_fs_cursor *fc,
 			     struct key *key,
 			     struct afs_vnode *vnode,
 			     struct afs_volsync *volsync,
@@ -325,9 +325,9 @@ int afs_fs_fetch_file_status(struct afs_server *server,
 	bp[2] = htonl(vnode->fid.vnode);
 	bp[3] = htonl(vnode->fid.unique);
 
-	call->cb_break = vnode->cb_break + server->cb_s_break;
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	call->cb_break = vnode->cb_break + fc->server->cb_s_break;
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -502,7 +502,7 @@ static const struct afs_call_type afs_RXFSFetchData64 = {
 /*
  * fetch data from a very large file
  */
-static int afs_fs_fetch_data64(struct afs_server *server,
+static int afs_fs_fetch_data64(struct afs_fs_cursor *fc,
 			       struct key *key,
 			       struct afs_vnode *vnode,
 			       struct afs_read *req,
@@ -536,15 +536,15 @@ static int afs_fs_fetch_data64(struct afs_server *server,
 	bp[7] = htonl(lower_32_bits(req->len));
 
 	atomic_inc(&req->usage);
-	call->cb_break = vnode->cb_break + server->cb_s_break;
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	call->cb_break = vnode->cb_break + fc->server->cb_s_break;
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
  * fetch data from a file
  */
-int afs_fs_fetch_data(struct afs_server *server,
+int afs_fs_fetch_data(struct afs_fs_cursor *fc,
 		      struct key *key,
 		      struct afs_vnode *vnode,
 		      struct afs_read *req,
@@ -557,7 +557,7 @@ int afs_fs_fetch_data(struct afs_server *server,
 	if (upper_32_bits(req->pos) ||
 	    upper_32_bits(req->len) ||
 	    upper_32_bits(req->pos + req->len))
-		return afs_fs_fetch_data64(server, key, vnode, req, async);
+		return afs_fs_fetch_data64(fc, key, vnode, req, async);
 
 	_enter("");
 
@@ -581,9 +581,9 @@ int afs_fs_fetch_data(struct afs_server *server,
 	bp[5] = htonl(lower_32_bits(req->len));
 
 	atomic_inc(&req->usage);
-	call->cb_break = vnode->cb_break + server->cb_s_break;
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	call->cb_break = vnode->cb_break + fc->server->cb_s_break;
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -625,7 +625,7 @@ static const struct afs_call_type afs_RXFSCreateXXXX = {
 /*
  * create a file or make a directory
  */
-int afs_fs_create(struct afs_server *server,
+int afs_fs_create(struct afs_fs_cursor *fc,
 		  struct key *key,
 		  struct afs_vnode *vnode,
 		  const char *name,
@@ -677,8 +677,8 @@ int afs_fs_create(struct afs_server *server,
 	*bp++ = htonl(mode & S_IALLUGO); /* unix mode */
 	*bp++ = 0; /* segment size */
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -717,7 +717,7 @@ static const struct afs_call_type afs_RXFSRemoveXXXX = {
 /*
  * remove a file or directory
  */
-int afs_fs_remove(struct afs_server *server,
+int afs_fs_remove(struct afs_fs_cursor *fc,
 		  struct key *key,
 		  struct afs_vnode *vnode,
 		  const char *name,
@@ -756,8 +756,8 @@ int afs_fs_remove(struct afs_server *server,
 		bp = (void *) bp + padsz;
 	}
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -797,7 +797,7 @@ static const struct afs_call_type afs_RXFSLink = {
 /*
  * make a hard link
  */
-int afs_fs_link(struct afs_server *server,
+int afs_fs_link(struct afs_fs_cursor *fc,
 		struct key *key,
 		struct afs_vnode *dvnode,
 		struct afs_vnode *vnode,
@@ -840,8 +840,8 @@ int afs_fs_link(struct afs_server *server,
 	*bp++ = htonl(vnode->fid.vnode);
 	*bp++ = htonl(vnode->fid.unique);
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -882,7 +882,7 @@ static const struct afs_call_type afs_RXFSSymlink = {
 /*
  * create a symbolic link
  */
-int afs_fs_symlink(struct afs_server *server,
+int afs_fs_symlink(struct afs_fs_cursor *fc,
 		   struct key *key,
 		   struct afs_vnode *vnode,
 		   const char *name,
@@ -943,8 +943,8 @@ int afs_fs_symlink(struct afs_server *server,
 	*bp++ = htonl(S_IRWXUGO); /* unix mode */
 	*bp++ = 0; /* segment size */
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -986,7 +986,7 @@ static const struct afs_call_type afs_RXFSRename = {
 /*
  * create a symbolic link
  */
-int afs_fs_rename(struct afs_server *server,
+int afs_fs_rename(struct afs_fs_cursor *fc,
 		  struct key *key,
 		  struct afs_vnode *orig_dvnode,
 		  const char *orig_name,
@@ -1045,8 +1045,8 @@ int afs_fs_rename(struct afs_server *server,
 		bp = (void *) bp + n_padsz;
 	}
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -1094,7 +1094,7 @@ static const struct afs_call_type afs_RXFSStoreData64 = {
 /*
  * store a set of pages to a very large file
  */
-static int afs_fs_store_data64(struct afs_server *server,
+static int afs_fs_store_data64(struct afs_fs_cursor *fc,
 			       struct afs_writeback *wb,
 			       pgoff_t first, pgoff_t last,
 			       unsigned offset, unsigned to,
@@ -1147,14 +1147,14 @@ static int afs_fs_store_data64(struct afs_server *server,
 	*bp++ = htonl(i_size >> 32);
 	*bp++ = htonl((u32) i_size);
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
  * store a set of pages
  */
-int afs_fs_store_data(struct afs_server *server, struct afs_writeback *wb,
+int afs_fs_store_data(struct afs_fs_cursor *fc, struct afs_writeback *wb,
 		      pgoff_t first, pgoff_t last,
 		      unsigned offset, unsigned to,
 		      bool async)
@@ -1183,7 +1183,7 @@ int afs_fs_store_data(struct afs_server *server, struct afs_writeback *wb,
 	       (unsigned long long) i_size);
 
 	if (pos >> 32 || i_size >> 32 || size >> 32 || (pos + size) >> 32)
-		return afs_fs_store_data64(server, wb, first, last, offset, to,
+		return afs_fs_store_data64(fc, wb, first, last, offset, to,
 					   size, pos, i_size, async);
 
 	call = afs_alloc_flat_call(net, &afs_RXFSStoreData,
@@ -1221,8 +1221,8 @@ int afs_fs_store_data(struct afs_server *server, struct afs_writeback *wb,
 	*bp++ = htonl(size);
 	*bp++ = htonl(i_size);
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -1279,7 +1279,7 @@ static const struct afs_call_type afs_RXFSStoreData64_as_Status = {
  * set the attributes on a very large file, using FS.StoreData rather than
  * FS.StoreStatus so as to alter the file size also
  */
-static int afs_fs_setattr_size64(struct afs_server *server, struct key *key,
+static int afs_fs_setattr_size64(struct afs_fs_cursor *fc, struct key *key,
 				 struct afs_vnode *vnode, struct iattr *attr,
 				 bool async)
 {
@@ -1319,15 +1319,15 @@ static int afs_fs_setattr_size64(struct afs_server *server, struct key *key,
 	*bp++ = htonl(attr->ia_size >> 32);	/* new file length */
 	*bp++ = htonl((u32) attr->ia_size);
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
  * set the attributes on a file, using FS.StoreData rather than FS.StoreStatus
  * so as to alter the file size also
  */
-static int afs_fs_setattr_size(struct afs_server *server, struct key *key,
+static int afs_fs_setattr_size(struct afs_fs_cursor *fc, struct key *key,
 			       struct afs_vnode *vnode, struct iattr *attr,
 			       bool async)
 {
@@ -1340,8 +1340,7 @@ static int afs_fs_setattr_size(struct afs_server *server, struct key *key,
 
 	ASSERT(attr->ia_valid & ATTR_SIZE);
 	if (attr->ia_size >> 32)
-		return afs_fs_setattr_size64(server, key, vnode, attr,
-					     async);
+		return afs_fs_setattr_size64(fc, key, vnode, attr, async);
 
 	call = afs_alloc_flat_call(net, &afs_RXFSStoreData_as_Status,
 				   (4 + 6 + 3) * 4,
@@ -1367,15 +1366,15 @@ static int afs_fs_setattr_size(struct afs_server *server, struct key *key,
 	*bp++ = 0;				/* size of write */
 	*bp++ = htonl(attr->ia_size);		/* new file length */
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
  * set the attributes on a file, using FS.StoreData if there's a change in file
  * size, and FS.StoreStatus otherwise
  */
-int afs_fs_setattr(struct afs_server *server, struct key *key,
+int afs_fs_setattr(struct afs_fs_cursor *fc, struct key *key,
 		   struct afs_vnode *vnode, struct iattr *attr,
 		   bool async)
 {
@@ -1384,8 +1383,7 @@ int afs_fs_setattr(struct afs_server *server, struct key *key,
 	__be32 *bp;
 
 	if (attr->ia_valid & ATTR_SIZE)
-		return afs_fs_setattr_size(server, key, vnode, attr,
-					   async);
+		return afs_fs_setattr_size(fc, key, vnode, attr, async);
 
 	_enter(",%x,{%x:%u},,",
 	       key_serial(key), vnode->fid.vid, vnode->fid.vnode);
@@ -1409,8 +1407,8 @@ int afs_fs_setattr(struct afs_server *server, struct key *key,
 
 	xdr_encode_AFS_StoreStatus(&bp, attr);
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -1607,7 +1605,7 @@ static const struct afs_call_type afs_RXFSGetVolumeStatus = {
 /*
  * fetch the status of a volume
  */
-int afs_fs_get_volume_status(struct afs_server *server,
+int afs_fs_get_volume_status(struct afs_fs_cursor *fc,
 			     struct key *key,
 			     struct afs_vnode *vnode,
 			     struct afs_volume_status *vs,
@@ -1640,8 +1638,8 @@ int afs_fs_get_volume_status(struct afs_server *server,
 	bp[0] = htonl(FSGETVOLUMESTATUS);
 	bp[1] = htonl(vnode->fid.vid);
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -1696,7 +1694,7 @@ static const struct afs_call_type afs_RXFSReleaseLock = {
 /*
  * get a lock on a file
  */
-int afs_fs_set_lock(struct afs_server *server,
+int afs_fs_set_lock(struct afs_fs_cursor *fc,
 		    struct key *key,
 		    struct afs_vnode *vnode,
 		    afs_lock_type_t type,
@@ -1723,14 +1721,14 @@ int afs_fs_set_lock(struct afs_server *server,
 	*bp++ = htonl(vnode->fid.unique);
 	*bp++ = htonl(type);
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
  * extend a lock on a file
  */
-int afs_fs_extend_lock(struct afs_server *server,
+int afs_fs_extend_lock(struct afs_fs_cursor *fc,
 		       struct key *key,
 		       struct afs_vnode *vnode,
 		       bool async)
@@ -1755,14 +1753,14 @@ int afs_fs_extend_lock(struct afs_server *server,
 	*bp++ = htonl(vnode->fid.vnode);
 	*bp++ = htonl(vnode->fid.unique);
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
  * release a lock on a file
  */
-int afs_fs_release_lock(struct afs_server *server,
+int afs_fs_release_lock(struct afs_fs_cursor *fc,
 			struct key *key,
 			struct afs_vnode *vnode,
 			bool async)
@@ -1787,8 +1785,8 @@ int afs_fs_release_lock(struct afs_server *server,
 	*bp++ = htonl(vnode->fid.vnode);
 	*bp++ = htonl(vnode->fid.unique);
 
-	afs_use_fs_server(call, server);
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	afs_use_fs_server(call, fc->server);
+	return afs_make_call(&fc->ac, call, GFP_NOFS, async);
 }
 
 /*
@@ -1812,6 +1810,7 @@ static const struct afs_call_type afs_RXFSGiveUpAllCallBacks = {
  * Flush all the callbacks we have on a server.
  */
 int afs_fs_give_up_all_callbacks(struct afs_server *server,
+				 struct afs_addr_cursor *ac,
 				 struct key *key,
 				 bool async)
 {
@@ -1831,5 +1830,5 @@ int afs_fs_give_up_all_callbacks(struct afs_server *server,
 	*bp++ = htonl(FSGIVEUPALLCALLBACKS);
 
 	/* Can't take a ref on server */
-	return afs_make_call(&server->addr, call, GFP_NOFS, async);
+	return afs_make_call(ac, call, GFP_NOFS, async);
 }
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 51e3825b5ffb..df52bf18a263 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -71,6 +71,17 @@ enum afs_call_state {
 };
 
 /*
+ * List of server addresses.
+ */
+struct afs_addr_list {
+	struct rcu_head		rcu;		/* Must be first */
+	refcount_t		usage;
+	unsigned short		nr_addrs;
+	unsigned short		index;		/* Address currently in use */
+	struct sockaddr_rxrpc	addrs[];
+};
+
+/*
  * a record of an in-progress RxRPC call
  */
 struct afs_call {
@@ -283,16 +294,15 @@ struct afs_cell {
 #define AFS_CELL_FL_NO_GC	1		/* The cell was added manually, don't auto-gc */
 #define AFS_CELL_FL_NOT_FOUND	2		/* Permanent DNS error */
 #define AFS_CELL_FL_DNS_FAIL	3		/* Failed to access DNS */
+#define AFS_CELL_FL_NO_LOOKUP_YET 4		/* Not completed first DNS lookup yet */
 	enum afs_cell_state	state;
 	short			error;
 
 	spinlock_t		vl_lock;	/* vl_list lock */
 
 	/* VLDB server list. */
-	seqlock_t		vl_addrs_lock;
-	unsigned short		vl_naddrs;	/* number of VL servers in addr list */
-	unsigned short		vl_curr_svix;	/* current server index */
-	struct sockaddr_rxrpc	vl_addrs[AFS_CELL_MAX_ADDRS];	/* cell VL server addresses */
+	rwlock_t		vl_addrs_lock;	/* Lock on vl_addrs */
+	struct afs_addr_list	__rcu *vl_addrs; /* List of VL servers */
 	u8			name_len;	/* Length of name */
 	char			name[64 + 1];	/* Cell name, case-flattened and NUL-padded */
 };
@@ -343,7 +353,7 @@ struct afs_vlocation {
 struct afs_server {
 	atomic_t		usage;
 	time64_t		time_of_death;	/* time at which put reduced usage to 0 */
-	struct sockaddr_rxrpc	addr;		/* server address */
+	struct afs_addr_list	__rcu *addrs;	/* List of addresses for this server */
 	struct afs_net		*net;		/* Network namespace in which the server resides */
 	struct afs_cell		*cell;		/* cell in which server resides */
 	struct list_head	link;		/* link in cell's server list */
@@ -485,8 +495,49 @@ struct afs_interface {
 	unsigned	mtu;		/* MTU of interface */
 };
 
+/*
+ * Cursor for iterating over a server's address list.
+ */
+struct afs_addr_cursor {
+	struct afs_addr_list	*alist;		/* Current address list (pins ref) */
+	struct sockaddr_rxrpc	*addr;
+	unsigned short		start;		/* Starting point in alist->addrs[] */
+	unsigned short		index;		/* Wrapping offset from start to current addr */
+	short			error;
+	bool			begun;		/* T if we've begun iteration */
+	bool			responded;	/* T if the current address responded */
+};
+
+/*
+ * Cursor for iterating over a set of fileservers.
+ */
+struct afs_fs_cursor {
+	struct afs_addr_cursor	ac;
+	struct afs_server	*server;	/* Current server (pins ref) */
+};
+
 /*****************************************************************************/
 /*
+ * addr_list.c
+ */
+static inline struct afs_addr_list *afs_get_addrlist(struct afs_addr_list *alist)
+{
+	if (alist)
+		refcount_inc(&alist->usage);
+	return alist;
+}
+extern struct afs_addr_list *afs_alloc_addrlist(unsigned int,
+						unsigned short,
+						unsigned short);
+extern void afs_put_addrlist(struct afs_addr_list *);
+extern struct afs_addr_list *afs_parse_text_addrs(const char *, size_t, char,
+						  unsigned short, unsigned short);
+extern struct afs_addr_list *afs_dns_query(struct afs_cell *, time64_t *);