/* -*- 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(struct work_struct *work) { 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); } void o2quo_exit(void) { flush_scheduled_work(); }