diff options
Diffstat (limited to 'fs/ocfs2/cluster/quorum.c')
| -rw-r--r-- | fs/ocfs2/cluster/quorum.c | 315 |
1 files changed, 315 insertions, 0 deletions
diff --git a/fs/ocfs2/cluster/quorum.c b/fs/ocfs2/cluster/quorum.c new file mode 100644 index 0000000000000..7bba98fbfc153 --- /dev/null +++ b/fs/ocfs2/cluster/quorum.c @@ -0,0 +1,315 @@ +/* -*- mode: c; c-basic-offset: 8; -*- + * + * vim: noexpandtab sw=8 ts=8 sts=0: + * + * Copyright (C) 2005 Oracle. All rights reserved. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public + * License as published by the Free Software Foundation; either + * version 2 of the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public + * License along with this program; if not, write to the + * Free Software Foundation, Inc., 59 Temple Place - Suite 330, + * Boston, MA 021110-1307, USA. + */ + +/* This quorum hack is only here until we transition to some more rational + * approach that is driven from userspace. Honest. No foolin'. + * + * Imagine two nodes lose network connectivity to each other but they're still + * up and operating in every other way. Presumably a network timeout indicates + * that a node is broken and should be recovered. They can't both recover each + * other and both carry on without serialising their access to the file system. + * They need to decide who is authoritative. Now extend that problem to + * arbitrary groups of nodes losing connectivity between each other. + * + * So we declare that a node which has given up on connecting to a majority + * of nodes who are still heartbeating will fence itself. + * + * There are huge opportunities for races here. After we give up on a node's + * connection we need to wait long enough to give heartbeat an opportunity + * to declare the node as truly dead. We also need to be careful with the + * race between when we see a node start heartbeating and when we connect + * to it. + * + * So nodes that are in this transtion put a hold on the quorum decision + * with a counter. As they fall out of this transition they drop the count + * and if they're the last, they fire off the decision. + */ +#include <linux/kernel.h> +#include <linux/slab.h> +#include <linux/workqueue.h> + +#include "heartbeat.h" +#include "nodemanager.h" +#define MLOG_MASK_PREFIX ML_QUORUM +#include "masklog.h" +#include "quorum.h" + +static struct o2quo_state { + spinlock_t qs_lock; + struct work_struct qs_work; + int qs_pending; + int qs_heartbeating; + unsigned long qs_hb_bm[BITS_TO_LONGS(O2NM_MAX_NODES)]; + int qs_connected; + unsigned long qs_conn_bm[BITS_TO_LONGS(O2NM_MAX_NODES)]; + int qs_holds; + unsigned long qs_hold_bm[BITS_TO_LONGS(O2NM_MAX_NODES)]; +} o2quo_state; + +/* this is horribly heavy-handed. It should instead flip the file + * system RO and call some userspace script. */ +static void o2quo_fence_self(void) +{ + /* panic spins with interrupts enabled. with preempt + * threads can still schedule, etc, etc */ + o2hb_stop_all_regions(); + panic("ocfs2 is very sorry to be fencing this system by panicing\n"); +} + +/* Indicate that a timeout occured on a hearbeat region write. The + * other nodes in the cluster may consider us dead at that time so we + * want to "fence" ourselves so that we don't scribble on the disk + * after they think they've recovered us. This can't solve all + * problems related to writeout after recovery but this hack can at + * least close some of those gaps. When we have real fencing, this can + * go away as our node would be fenced externally before other nodes + * begin recovery. */ +void o2quo_disk_timeout(void) +{ + o2quo_fence_self(); +} + +static void o2quo_make_decision(void *arg) +{ + int quorum; + int lowest_hb, lowest_reachable = 0, fence = 0; + struct o2quo_state *qs = &o2quo_state; + + spin_lock(&qs->qs_lock); + + lowest_hb = find_first_bit(qs->qs_hb_bm, O2NM_MAX_NODES); + if (lowest_hb != O2NM_MAX_NODES) + lowest_reachable = test_bit(lowest_hb, qs->qs_conn_bm); + + mlog(0, "heartbeating: %d, connected: %d, " + "lowest: %d (%sreachable)\n", qs->qs_heartbeating, + qs->qs_connected, lowest_hb, lowest_reachable ? "" : "un"); + + if (!test_bit(o2nm_this_node(), qs->qs_hb_bm) || + qs->qs_heartbeating == 1) + goto out; + + if (qs->qs_heartbeating & 1) { + /* the odd numbered cluster case is straight forward -- + * if we can't talk to the majority we're hosed */ + quorum = (qs->qs_heartbeating + 1)/2; + if (qs->qs_connected < quorum) { + mlog(ML_ERROR, "fencing this node because it is " + "only connected to %u nodes and %u is needed " + "to make a quorum out of %u heartbeating nodes\n", + qs->qs_connected, quorum, + qs->qs_heartbeating); + fence = 1; + } + } else { + /* the even numbered cluster adds the possibility of each half + * of the cluster being able to talk amongst themselves.. in + * that case we're hosed if we can't talk to the group that has + * the lowest numbered node */ + quorum = qs->qs_heartbeating / 2; + if (qs->qs_connected < quorum) { + mlog(ML_ERROR, "fencing this node because it is " + "only connected to %u nodes and %u is needed " + "to make a quorum out of %u heartbeating nodes\n", + qs->qs_connected, quorum, + qs->qs_heartbeating); + fence = 1; + } + else if ((qs->qs_connected == quorum) && + !lowest_reachable) { + mlog(ML_ERROR, "fencing this node because it is " + "connected to a half-quorum of %u out of %u " + "nodes which doesn't include the lowest active " + "node %u\n", quorum, qs->qs_heartbeating, + lowest_hb); + fence = 1; + } + } + +out: + spin_unlock(&qs->qs_lock); + if (fence) + o2quo_fence_self(); +} + +static void o2quo_set_hold(struct o2quo_state *qs, u8 node) +{ + assert_spin_locked(&qs->qs_lock); + + if (!test_and_set_bit(node, qs->qs_hold_bm)) { + qs->qs_holds++; + mlog_bug_on_msg(qs->qs_holds == O2NM_MAX_NODES, + "node %u\n", node); + mlog(0, "node %u, %d total\n", node, qs->qs_holds); + } +} + +static void o2quo_clear_hold(struct o2quo_state *qs, u8 node) +{ + assert_spin_locked(&qs->qs_lock); + + if (test_and_clear_bit(node, qs->qs_hold_bm)) { + mlog(0, "node %u, %d total\n", node, qs->qs_holds - 1); + if (--qs->qs_holds == 0) { + if (qs->qs_pending) { + qs->qs_pending = 0; + schedule_work(&qs->qs_work); + } + } + mlog_bug_on_msg(qs->qs_holds < 0, "node %u, holds %d\n", + node, qs->qs_holds); + } +} + +/* as a node comes up we delay the quorum decision until we know the fate of + * the connection. the hold will be droped in conn_up or hb_down. it might be + * perpetuated by con_err until hb_down. if we already have a conn, we might + * be dropping a hold that conn_up got. */ +void o2quo_hb_up(u8 node) +{ + struct o2quo_state *qs = &o2quo_state; + + spin_lock(&qs->qs_lock); + + qs->qs_heartbeating++; + mlog_bug_on_msg(qs->qs_heartbeating == O2NM_MAX_NODES, + "node %u\n", node); + mlog_bug_on_msg(test_bit(node, qs->qs_hb_bm), "node %u\n", node); + set_bit(node, qs->qs_hb_bm); + + mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating); + + if (!test_bit(node, qs->qs_conn_bm)) + o2quo_set_hold(qs, node); + else + o2quo_clear_hold(qs, node); + + spin_unlock(&qs->qs_lock); +} + +/* hb going down releases any holds we might have had due to this node from + * conn_up, conn_err, or hb_up */ +void o2quo_hb_down(u8 node) +{ + struct o2quo_state *qs = &o2quo_state; + + spin_lock(&qs->qs_lock); + + qs->qs_heartbeating--; + mlog_bug_on_msg(qs->qs_heartbeating < 0, + "node %u, %d heartbeating\n", + node, qs->qs_heartbeating); + mlog_bug_on_msg(!test_bit(node, qs->qs_hb_bm), "node %u\n", node); + clear_bit(node, qs->qs_hb_bm); + + mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating); + + o2quo_clear_hold(qs, node); + + spin_unlock(&qs->qs_lock); +} + +/* this tells us that we've decided that the node is still heartbeating + * even though we've lost it's conn. it must only be called after conn_err + * and indicates that we must now make a quorum decision in the future, + * though we might be doing so after waiting for holds to drain. Here + * we'll be dropping the hold from conn_err. */ +void o2quo_hb_still_up(u8 node) +{ + struct o2quo_state *qs = &o2quo_state; + + spin_lock(&qs->qs_lock); + + mlog(0, "node %u\n", node); + + qs->qs_pending = 1; + o2quo_clear_hold(qs, node); + + spin_unlock(&qs->qs_lock); +} + +/* This is analagous to hb_up. as a node's connection comes up we delay the + * quorum decision until we see it heartbeating. the hold will be droped in + * hb_up or hb_down. it might be perpetuated by con_err until hb_down. if + * it's already heartbeating we we might be dropping a hold that conn_up got. + * */ +void o2quo_conn_up(u8 node) +{ + struct o2quo_state *qs = &o2quo_state; + + spin_lock(&qs->qs_lock); + + qs->qs_connected++; + mlog_bug_on_msg(qs->qs_connected == O2NM_MAX_NODES, + "node %u\n", node); + mlog_bug_on_msg(test_bit(node, qs->qs_conn_bm), "node %u\n", node); + set_bit(node, qs->qs_conn_bm); + + mlog(0, "node %u, %d total\n", node, qs->qs_connected); + + if (!test_bit(node, qs->qs_hb_bm)) + o2quo_set_hold(qs, node); + else + o2quo_clear_hold(qs, node); + + spin_unlock(&qs->qs_lock); +} + +/* we've decided that we won't ever be connecting to the node again. if it's + * still heartbeating we grab a hold that will delay decisions until either the + * node stops heartbeating from hb_down or the caller decides that the node is + * still up and calls still_up */ +void o2quo_conn_err(u8 node) +{ + struct o2quo_state *qs = &o2quo_state; + + spin_lock(&qs->qs_lock); + + if (test_bit(node, qs->qs_conn_bm)) { + qs->qs_connected--; + mlog_bug_on_msg(qs->qs_connected < 0, + "node %u, connected %d\n", + node, qs->qs_connected); + + clear_bit(node, qs->qs_conn_bm); + } + + mlog(0, "node %u, %d total\n", node, qs->qs_connected); + + if (test_bit(node, qs->qs_hb_bm)) + o2quo_set_hold(qs, node); + + spin_unlock(&qs->qs_lock); +} + +void o2quo_init(void) +{ + struct o2quo_state *qs = &o2quo_state; + + spin_lock_init(&qs->qs_lock); + INIT_WORK(&qs->qs_work, o2quo_make_decision, NULL); +} + +void o2quo_exit(void) +{ + flush_scheduled_work(); +} |