linux/fs/afs/rotate.c
David Howells 4fe6a94682 afs: Try to avoid taking RCU read lock when checking vnode validity
Try to avoid taking the RCU read lock when checking the validity of a
vnode's callback state.  The only thing it's needed for is to pin the
parent volume's server list whilst we search it to find the record of the
server we're currently using to see if it has been reinitialised (ie. it
sent us a CB.InitCallBackState* RPC).

Do this by the following means:

 (1) Keep an additional per-cell counter (fs_s_break) that's incremented
     each time any of the fileservers in the cell reinitialises.

     Since the new counter can be accessed without RCU from the vnode, we
     can check that first - and only if it differs, get the RCU read lock
     and check the volume's server list.

 (2) Replace afs_get_s_break_rcu() with afs_check_server_good() which now
     indicates whether the callback promise is still expected to be present
     on the server.  This does the checks as described in (1).

 (3) Restructure afs_check_validity() to take account of the change in (2).

     We can also get rid of the valid variable and just use the need_clear
     variable with the addition of the afs_cb_break_no_promise reason.

 (4) afs_check_validity() probably shouldn't be altering vnode->cb_v_break
     and vnode->cb_s_break when it doesn't have cb_lock exclusively locked.

     Move the change to vnode->cb_v_break to __afs_break_callback().

     Delegate the change to vnode->cb_s_break to afs_select_fileserver()
     and set vnode->cb_fs_s_break there also.

 (5) afs_validate() no longer needs to get the RCU read lock around its
     call to afs_check_validity() - and can skip the call entirely if we
     don't have a promise.

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Markus Suvanto <markus.suvanto@gmail.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/163111669583.283156.1397603105683094563.stgit@warthog.procyon.org.uk/
2021-09-13 09:10:39 +01:00

515 lines
13 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/* Handle fileserver selection and rotation.
*
* Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/sched/signal.h>
#include "internal.h"
#include "afs_fs.h"
/*
* Begin iteration through a server list, starting with the vnode's last used
* server if possible, or the last recorded good server if not.
*/
static bool afs_start_fs_iteration(struct afs_operation *op,
struct afs_vnode *vnode)
{
struct afs_server *server;
void *cb_server;
int i;
read_lock(&op->volume->servers_lock);
op->server_list = afs_get_serverlist(
rcu_dereference_protected(op->volume->servers,
lockdep_is_held(&op->volume->servers_lock)));
read_unlock(&op->volume->servers_lock);
op->untried = (1UL << op->server_list->nr_servers) - 1;
op->index = READ_ONCE(op->server_list->preferred);
cb_server = vnode->cb_server;
if (cb_server) {
/* See if the vnode's preferred record is still available */
for (i = 0; i < op->server_list->nr_servers; i++) {
server = op->server_list->servers[i].server;
if (server == cb_server) {
op->index = i;
goto found_interest;
}
}
/* If we have a lock outstanding on a server that's no longer
* serving this vnode, then we can't switch to another server
* and have to return an error.
*/
if (op->flags & AFS_OPERATION_CUR_ONLY) {
op->error = -ESTALE;
return false;
}
/* Note that the callback promise is effectively broken */
write_seqlock(&vnode->cb_lock);
ASSERTCMP(cb_server, ==, vnode->cb_server);
vnode->cb_server = NULL;
if (test_and_clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags))
vnode->cb_break++;
write_sequnlock(&vnode->cb_lock);
}
found_interest:
return true;
}
/*
* Post volume busy note.
*/
static void afs_busy(struct afs_volume *volume, u32 abort_code)
{
const char *m;
switch (abort_code) {
case VOFFLINE: m = "offline"; break;
case VRESTARTING: m = "restarting"; break;
case VSALVAGING: m = "being salvaged"; break;
default: m = "busy"; break;
}
pr_notice("kAFS: Volume %llu '%s' is %s\n", volume->vid, volume->name, m);
}
/*
* Sleep and retry the operation to the same fileserver.
*/
static bool afs_sleep_and_retry(struct afs_operation *op)
{
if (!(op->flags & AFS_OPERATION_UNINTR)) {
msleep_interruptible(1000);
if (signal_pending(current)) {
op->error = -ERESTARTSYS;
return false;
}
} else {
msleep(1000);
}
return true;
}
/*
* Select the fileserver to use. May be called multiple times to rotate
* through the fileservers.
*/
bool afs_select_fileserver(struct afs_operation *op)
{
struct afs_addr_list *alist;
struct afs_server *server;
struct afs_vnode *vnode = op->file[0].vnode;
struct afs_error e;
u32 rtt;
int error = op->ac.error, i;
_enter("%lx[%d],%lx[%d],%d,%d",
op->untried, op->index,
op->ac.tried, op->ac.index,
error, op->ac.abort_code);
if (op->flags & AFS_OPERATION_STOP) {
_leave(" = f [stopped]");
return false;
}
op->nr_iterations++;
/* Evaluate the result of the previous operation, if there was one. */
switch (error) {
case SHRT_MAX:
goto start;
case 0:
default:
/* Success or local failure. Stop. */
op->error = error;
op->flags |= AFS_OPERATION_STOP;
_leave(" = f [okay/local %d]", error);
return false;
case -ECONNABORTED:
/* The far side rejected the operation on some grounds. This
* might involve the server being busy or the volume having been moved.
*/
switch (op->ac.abort_code) {
case VNOVOL:
/* This fileserver doesn't know about the volume.
* - May indicate that the VL is wrong - retry once and compare
* the results.
* - May indicate that the fileserver couldn't attach to the vol.
*/
if (op->flags & AFS_OPERATION_VNOVOL) {
op->error = -EREMOTEIO;
goto next_server;
}
write_lock(&op->volume->servers_lock);
op->server_list->vnovol_mask |= 1 << op->index;
write_unlock(&op->volume->servers_lock);
set_bit(AFS_VOLUME_NEEDS_UPDATE, &op->volume->flags);
error = afs_check_volume_status(op->volume, op);
if (error < 0)
goto failed_set_error;
if (test_bit(AFS_VOLUME_DELETED, &op->volume->flags)) {
op->error = -ENOMEDIUM;
goto failed;
}
/* If the server list didn't change, then assume that
* it's the fileserver having trouble.
*/
if (rcu_access_pointer(op->volume->servers) == op->server_list) {
op->error = -EREMOTEIO;
goto next_server;
}
/* Try again */
op->flags |= AFS_OPERATION_VNOVOL;
_leave(" = t [vnovol]");
return true;
case VSALVAGE: /* TODO: Should this return an error or iterate? */
case VVOLEXISTS:
case VNOSERVICE:
case VONLINE:
case VDISKFULL:
case VOVERQUOTA:
op->error = afs_abort_to_error(op->ac.abort_code);
goto next_server;
case VOFFLINE:
if (!test_and_set_bit(AFS_VOLUME_OFFLINE, &op->volume->flags)) {
afs_busy(op->volume, op->ac.abort_code);
clear_bit(AFS_VOLUME_BUSY, &op->volume->flags);
}
if (op->flags & AFS_OPERATION_NO_VSLEEP) {
op->error = -EADV;
goto failed;
}
if (op->flags & AFS_OPERATION_CUR_ONLY) {
op->error = -ESTALE;
goto failed;
}
goto busy;
case VSALVAGING:
case VRESTARTING:
case VBUSY:
/* Retry after going round all the servers unless we
* have a file lock we need to maintain.
*/
if (op->flags & AFS_OPERATION_NO_VSLEEP) {
op->error = -EBUSY;
goto failed;
}
if (!test_and_set_bit(AFS_VOLUME_BUSY, &op->volume->flags)) {
afs_busy(op->volume, op->ac.abort_code);
clear_bit(AFS_VOLUME_OFFLINE, &op->volume->flags);
}
busy:
if (op->flags & AFS_OPERATION_CUR_ONLY) {
if (!afs_sleep_and_retry(op))
goto failed;
/* Retry with same server & address */
_leave(" = t [vbusy]");
return true;
}
op->flags |= AFS_OPERATION_VBUSY;
goto next_server;
case VMOVED:
/* The volume migrated to another server. We consider
* consider all locks and callbacks broken and request
* an update from the VLDB.
*
* We also limit the number of VMOVED hops we will
* honour, just in case someone sets up a loop.
*/
if (op->flags & AFS_OPERATION_VMOVED) {
op->error = -EREMOTEIO;
goto failed;
}
op->flags |= AFS_OPERATION_VMOVED;
set_bit(AFS_VOLUME_WAIT, &op->volume->flags);
set_bit(AFS_VOLUME_NEEDS_UPDATE, &op->volume->flags);
error = afs_check_volume_status(op->volume, op);
if (error < 0)
goto failed_set_error;
/* If the server list didn't change, then the VLDB is
* out of sync with the fileservers. This is hopefully
* a temporary condition, however, so we don't want to
* permanently block access to the file.
*
* TODO: Try other fileservers if we can.
*
* TODO: Retry a few times with sleeps.
*/
if (rcu_access_pointer(op->volume->servers) == op->server_list) {
op->error = -ENOMEDIUM;
goto failed;
}
goto restart_from_beginning;
default:
clear_bit(AFS_VOLUME_OFFLINE, &op->volume->flags);
clear_bit(AFS_VOLUME_BUSY, &op->volume->flags);
op->error = afs_abort_to_error(op->ac.abort_code);
goto failed;
}
case -ETIMEDOUT:
case -ETIME:
if (op->error != -EDESTADDRREQ)
goto iterate_address;
fallthrough;
case -ERFKILL:
case -EADDRNOTAVAIL:
case -ENETUNREACH:
case -EHOSTUNREACH:
case -EHOSTDOWN:
case -ECONNREFUSED:
_debug("no conn");
op->error = error;
goto iterate_address;
case -ECONNRESET:
_debug("call reset");
op->error = error;
goto failed;
}
restart_from_beginning:
_debug("restart");
afs_end_cursor(&op->ac);
op->server = NULL;
afs_put_serverlist(op->net, op->server_list);
op->server_list = NULL;
start:
_debug("start");
/* See if we need to do an update of the volume record. Note that the
* volume may have moved or even have been deleted.
*/
error = afs_check_volume_status(op->volume, op);
if (error < 0)
goto failed_set_error;
if (!afs_start_fs_iteration(op, vnode))
goto failed;
_debug("__ VOL %llx __", op->volume->vid);
pick_server:
_debug("pick [%lx]", op->untried);
error = afs_wait_for_fs_probes(op->server_list, op->untried);
if (error < 0)
goto failed_set_error;
/* Pick the untried server with the lowest RTT. If we have outstanding
* callbacks, we stick with the server we're already using if we can.
*/
if (op->server) {
_debug("server %u", op->index);
if (test_bit(op->index, &op->untried))
goto selected_server;
op->server = NULL;
_debug("no server");
}
op->index = -1;
rtt = U32_MAX;
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) ||
!test_bit(AFS_SERVER_FL_RESPONDING, &s->flags))
continue;
if (s->probe.rtt < rtt) {
op->index = i;
rtt = s->probe.rtt;
}
}
if (op->index == -1)
goto no_more_servers;
selected_server:
_debug("use %d", op->index);
__clear_bit(op->index, &op->untried);
/* We're starting on a different fileserver from the list. We need to
* check it, create a callback intercept, find its address list and
* probe its capabilities before we use it.
*/
ASSERTCMP(op->ac.alist, ==, NULL);
server = op->server_list->servers[op->index].server;
if (!afs_check_server_record(op, server))
goto failed;
_debug("USING SERVER: %pU", &server->uuid);
op->flags |= AFS_OPERATION_RETRY_SERVER;
op->server = server;
if (vnode->cb_server != server) {
vnode->cb_server = server;
vnode->cb_s_break = server->cb_s_break;
vnode->cb_fs_s_break = atomic_read(&server->cell->fs_s_break);
vnode->cb_v_break = vnode->volume->cb_v_break;
clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags);
}
read_lock(&server->fs_lock);
alist = rcu_dereference_protected(server->addresses,
lockdep_is_held(&server->fs_lock));
afs_get_addrlist(alist);
read_unlock(&server->fs_lock);
retry_server:
memset(&op->ac, 0, sizeof(op->ac));
if (!op->ac.alist)
op->ac.alist = alist;
else
afs_put_addrlist(alist);
op->ac.index = -1;
iterate_address:
ASSERT(op->ac.alist);
/* Iterate over the current server's address list to try and find an
* address on which it will respond to us.
*/
if (!afs_iterate_addresses(&op->ac))
goto out_of_addresses;
_debug("address [%u] %u/%u %pISp",
op->index, op->ac.index, op->ac.alist->nr_addrs,
&op->ac.alist->addrs[op->ac.index].transport);
_leave(" = t");
return true;
out_of_addresses:
/* We've now had a failure to respond on all of a server's addresses -
* immediately probe them again and consider retrying the server.
*/
afs_probe_fileserver(op->net, op->server);
if (op->flags & AFS_OPERATION_RETRY_SERVER) {
alist = op->ac.alist;
error = afs_wait_for_one_fs_probe(
op->server, !(op->flags & AFS_OPERATION_UNINTR));
switch (error) {
case 0:
op->flags &= ~AFS_OPERATION_RETRY_SERVER;
goto retry_server;
case -ERESTARTSYS:
goto failed_set_error;
case -ETIME:
case -EDESTADDRREQ:
goto next_server;
}
}
next_server:
_debug("next");
afs_end_cursor(&op->ac);
goto pick_server;
no_more_servers:
/* That's all the servers poked to no good effect. Try again if some
* of them were busy.
*/
if (op->flags & AFS_OPERATION_VBUSY)
goto restart_from_beginning;
e.error = -EDESTADDRREQ;
e.responded = false;
for (i = 0; i < op->server_list->nr_servers; i++) {
struct afs_server *s = op->server_list->servers[i].server;
afs_prioritise_error(&e, READ_ONCE(s->probe.error),
s->probe.abort_code);
}
error = e.error;
failed_set_error:
op->error = error;
failed:
op->flags |= AFS_OPERATION_STOP;
afs_end_cursor(&op->ac);
_leave(" = f [failed %d]", op->error);
return false;
}
/*
* Dump cursor state in the case of the error being EDESTADDRREQ.
*/
void afs_dump_edestaddrreq(const struct afs_operation *op)
{
static int count;
int i;
if (!IS_ENABLED(CONFIG_AFS_DEBUG_CURSOR) || count > 3)
return;
count++;
rcu_read_lock();
pr_notice("EDESTADDR occurred\n");
pr_notice("FC: cbb=%x cbb2=%x fl=%x err=%hd\n",
op->file[0].cb_break_before,
op->file[1].cb_break_before, op->flags, op->error);
pr_notice("FC: ut=%lx ix=%d ni=%u\n",
op->untried, op->index, op->nr_iterations);
if (op->server_list) {
const struct afs_server_list *sl = op->server_list;
pr_notice("FC: SL nr=%u pr=%u vnov=%hx\n",
sl->nr_servers, sl->preferred, sl->vnovol_mask);
for (i = 0; i < sl->nr_servers; i++) {
const struct afs_server *s = sl->servers[i].server;
pr_notice("FC: server fl=%lx av=%u %pU\n",
s->flags, s->addr_version, &s->uuid);
if (s->addresses) {
const struct afs_addr_list *a =
rcu_dereference(s->addresses);
pr_notice("FC: - av=%u nr=%u/%u/%u pr=%u\n",
a->version,
a->nr_ipv4, a->nr_addrs, a->max_addrs,
a->preferred);
pr_notice("FC: - R=%lx F=%lx\n",
a->responded, a->failed);
if (a == op->ac.alist)
pr_notice("FC: - current\n");
}
}
}
pr_notice("AC: t=%lx ax=%u ac=%d er=%d r=%u ni=%u\n",
op->ac.tried, op->ac.index, op->ac.abort_code, op->ac.error,
op->ac.responded, op->ac.nr_iterations);
rcu_read_unlock();
}