afs: Don't use probe running state to make decisions outside probe code

Don't use the running state for fileserver probes to make decisions about
which server to use as the state is cleared at the start of a probe and
also intermediate values might be misleading.

Instead, add a separate 'latest known' rtt in the afs_server struct and a
flag to indicate if the server is known to be responding and update these
as and when we know what to change them to.

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

4 files changed, 18 insertions, 8 deletions

diff --git a/fs/afs/fs_probe.c b/fs/afs/fs_probe.c
index 442b5e7944ff..c41cf3b2ab89 100644
--- a/fs/afs/fs_probe.c
+++ b/fs/afs/fs_probe.c
@@ -42,10 +42,13 @@ static void afs_finished_fs_probe(struct afs_net *net, struct afs_server *server
 	bool responded = server->probe.responded;
 
 	write_seqlock(&net->fs_lock);
-	if (responded)
+	if (responded) {
 		list_add_tail(&server->probe_link, &net->fs_probe_slow);
-	else
+	} else {
+		server->rtt = UINT_MAX;
+		clear_bit(AFS_SERVER_FL_RESPONDING, &server->flags);
 		list_add_tail(&server->probe_link, &net->fs_probe_fast);
+	}
 	write_sequnlock(&net->fs_lock);
 
 	afs_schedule_fs_probe(net, server, !responded);
@@ -161,12 +164,14 @@ responded:
 	rtt_us = rxrpc_kernel_get_srtt(call->net->socket, call->rxcall);
 	if (rtt_us < server->probe.rtt) {
 		server->probe.rtt = rtt_us;
+		server->rtt = rtt_us;
 		alist->preferred = index;
 	}
 
 	smp_wmb(); /* Set rtt before responded. */
 	server->probe.responded = true;
 	set_bit(index, &alist->responded);
+	set_bit(AFS_SERVER_FL_RESPONDING, &server->flags);
 out:
 	spin_unlock(&server->probe_lock);
 
@@ -224,7 +229,7 @@ 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;
+	unsigned int rtt = UINT_MAX, rtt_s;
 	bool have_responders = false;
 	int pref = -1, i;
 
@@ -280,10 +285,11 @@ stop:
 	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) {
+			rtt_s = READ_ONCE(server->rtt);
+			if (test_bit(AFS_SERVER_FL_RESPONDING, &server->flags) &&
+			    rtt_s < rtt) {
 				pref = i;
-				rtt = server->probe.rtt;
+				rtt = rtt_s;
 			}
 
 			remove_wait_queue(&server->probe_wq, &waits[i]);
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index e0dc14d4d8b9..a4fe5d1a8b53 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -496,6 +496,7 @@ struct afs_server {
 	struct afs_server	*gc_next;	/* Next server in manager's list */
 	time64_t		unuse_time;	/* Time at which last unused */
 	unsigned long		flags;
+#define AFS_SERVER_FL_RESPONDING 0		/* The server is responding */
 #define AFS_SERVER_FL_NOT_READY	1		/* The record is not ready for use */
 #define AFS_SERVER_FL_NOT_FOUND	2		/* VL server says no such server */
 #define AFS_SERVER_FL_VL_FAIL	3		/* Failed to access VL server */
@@ -508,6 +509,7 @@ struct afs_server {
 	atomic_t		ref;		/* Object refcount */
 	atomic_t		active;		/* Active user count */
 	u32			addr_version;	/* Address list version */
+	unsigned int		rtt;		/* Server's current RTT in uS */
 	unsigned int		debug_id;	/* Debugging ID for traces */
 
 	/* file service access */
@@ -522,7 +524,7 @@ struct afs_server {
 	atomic_t		probe_outstanding;
 	spinlock_t		probe_lock;
 	struct {
-		unsigned int	rtt;		/* RTT as ktime/64 */
+		unsigned int	rtt;		/* RTT in uS */
 		u32		abort_code;
 		short		error;
 		bool		responded:1;
diff --git a/fs/afs/rotate.c b/fs/afs/rotate.c
index 8d5473cd8ea4..14863678ae9e 100644
--- a/fs/afs/rotate.c
+++ b/fs/afs/rotate.c
@@ -341,7 +341,8 @@ pick_server:
 	for (i = 0; i < op->server_list->nr_servers; i++) {
 		struct afs_server *s = op->server_list->servers[i].server;
 
-		if (!test_bit(i, &op->untried) || !s->probe.responded)
+		if (!test_bit(i, &op->untried) ||
+		    !test_bit(AFS_SERVER_FL_RESPONDING, &s->flags))
 			continue;
 		if (s->probe.rtt < rtt) {
 			op->index = i;
diff --git a/fs/afs/server.c b/fs/afs/server.c
index 88593ffcb54e..039e3488511c 100644
--- a/fs/afs/server.c
+++ b/fs/afs/server.c
@@ -239,6 +239,7 @@ static struct afs_server *afs_alloc_server(struct afs_cell *cell,
 	INIT_LIST_HEAD(&server->probe_link);
 	spin_lock_init(&server->probe_lock);
 	server->cell = cell;
+	server->rtt = UINT_MAX;
 
 	afs_inc_servers_outstanding(net);
 	trace_afs_server(server, 1, 1, afs_server_trace_alloc);