[PATCH 25/27] afs: Don't use probe running state to make decisions outside probe code

David Howells
2020-05-29T22:03:27Z

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>
---

fs/afs/fs_probe.c | 18 ++++++++++++------
fs/afs/internal.h | 4 +++-
fs/afs/rotate.c | 3 ++-
fs/afs/server.c | 1 +
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 @@ void afs_fileserver_probe_result(struct afs_call *call)
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 @@ int afs_wait_for_fs_probes(struct afs_server_list *slist, unsigned long untried)
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 979979e33a77..d1590fb382b6 100644
--- a/fs/afs/rotate.c
+++ b/fs/afs/rotate.c
@@ -339,7 +339,8 @@ bool afs_select_fileserver(struct afs_operation *op)
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);