1 /* -*- mode: c; c-basic-offset: 8; -*- 2 * 3 * vim: noexpandtab sw=8 ts=8 sts=0: 4 * 5 * Copyright (C) 2005 Oracle. All rights reserved. 6 * 7 * This program is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU General Public 9 * License as published by the Free Software Foundation; either 10 * version 2 of the License, or (at your option) any later version. 11 * 12 * This program is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * General Public License for more details. 16 * 17 * You should have received a copy of the GNU General Public 18 * License along with this program; if not, write to the 19 * Free Software Foundation, Inc., 59 Temple Place - Suite 330, 20 * Boston, MA 021110-1307, USA. 21 */ 22 23 /* This quorum hack is only here until we transition to some more rational 24 * approach that is driven from userspace. Honest. No foolin'. 25 * 26 * Imagine two nodes lose network connectivity to each other but they're still 27 * up and operating in every other way. Presumably a network timeout indicates 28 * that a node is broken and should be recovered. They can't both recover each 29 * other and both carry on without serialising their access to the file system. 30 * They need to decide who is authoritative. Now extend that problem to 31 * arbitrary groups of nodes losing connectivity between each other. 32 * 33 * So we declare that a node which has given up on connecting to a majority 34 * of nodes who are still heartbeating will fence itself. 35 * 36 * There are huge opportunities for races here. After we give up on a node's 37 * connection we need to wait long enough to give heartbeat an opportunity 38 * to declare the node as truly dead. We also need to be careful with the 39 * race between when we see a node start heartbeating and when we connect 40 * to it. 41 * 42 * So nodes that are in this transtion put a hold on the quorum decision 43 * with a counter. As they fall out of this transition they drop the count 44 * and if they're the last, they fire off the decision. 45 */ 46 #include <linux/kernel.h> 47 #include <linux/slab.h> 48 #include <linux/workqueue.h> 49 #include <linux/reboot.h> 50 51 #include "heartbeat.h" 52 #include "nodemanager.h" 53 #define MLOG_MASK_PREFIX ML_QUORUM 54 #include "masklog.h" 55 #include "quorum.h" 56 57 static struct o2quo_state { 58 spinlock_t qs_lock; 59 struct work_struct qs_work; 60 int qs_pending; 61 int qs_heartbeating; 62 unsigned long qs_hb_bm[BITS_TO_LONGS(O2NM_MAX_NODES)]; 63 int qs_connected; 64 unsigned long qs_conn_bm[BITS_TO_LONGS(O2NM_MAX_NODES)]; 65 int qs_holds; 66 unsigned long qs_hold_bm[BITS_TO_LONGS(O2NM_MAX_NODES)]; 67 } o2quo_state; 68 69 /* this is horribly heavy-handed. It should instead flip the file 70 * system RO and call some userspace script. */ 71 static void o2quo_fence_self(void) 72 { 73 /* panic spins with interrupts enabled. with preempt 74 * threads can still schedule, etc, etc */ 75 o2hb_stop_all_regions(); 76 77 printk("ocfs2 is very sorry to be fencing this system by restarting\n"); 78 emergency_restart(); 79 } 80 81 /* Indicate that a timeout occured on a hearbeat region write. The 82 * other nodes in the cluster may consider us dead at that time so we 83 * want to "fence" ourselves so that we don't scribble on the disk 84 * after they think they've recovered us. This can't solve all 85 * problems related to writeout after recovery but this hack can at 86 * least close some of those gaps. When we have real fencing, this can 87 * go away as our node would be fenced externally before other nodes 88 * begin recovery. */ 89 void o2quo_disk_timeout(void) 90 { 91 o2quo_fence_self(); 92 } 93 94 static void o2quo_make_decision(struct work_struct *work) 95 { 96 int quorum; 97 int lowest_hb, lowest_reachable = 0, fence = 0; 98 struct o2quo_state *qs = &o2quo_state; 99 100 spin_lock(&qs->qs_lock); 101 102 lowest_hb = find_first_bit(qs->qs_hb_bm, O2NM_MAX_NODES); 103 if (lowest_hb != O2NM_MAX_NODES) 104 lowest_reachable = test_bit(lowest_hb, qs->qs_conn_bm); 105 106 mlog(0, "heartbeating: %d, connected: %d, " 107 "lowest: %d (%sreachable)\n", qs->qs_heartbeating, 108 qs->qs_connected, lowest_hb, lowest_reachable ? "" : "un"); 109 110 if (!test_bit(o2nm_this_node(), qs->qs_hb_bm) || 111 qs->qs_heartbeating == 1) 112 goto out; 113 114 if (qs->qs_heartbeating & 1) { 115 /* the odd numbered cluster case is straight forward -- 116 * if we can't talk to the majority we're hosed */ 117 quorum = (qs->qs_heartbeating + 1)/2; 118 if (qs->qs_connected < quorum) { 119 mlog(ML_ERROR, "fencing this node because it is " 120 "only connected to %u nodes and %u is needed " 121 "to make a quorum out of %u heartbeating nodes\n", 122 qs->qs_connected, quorum, 123 qs->qs_heartbeating); 124 fence = 1; 125 } 126 } else { 127 /* the even numbered cluster adds the possibility of each half 128 * of the cluster being able to talk amongst themselves.. in 129 * that case we're hosed if we can't talk to the group that has 130 * the lowest numbered node */ 131 quorum = qs->qs_heartbeating / 2; 132 if (qs->qs_connected < quorum) { 133 mlog(ML_ERROR, "fencing this node because it is " 134 "only connected to %u nodes and %u is needed " 135 "to make a quorum out of %u heartbeating nodes\n", 136 qs->qs_connected, quorum, 137 qs->qs_heartbeating); 138 fence = 1; 139 } 140 else if ((qs->qs_connected == quorum) && 141 !lowest_reachable) { 142 mlog(ML_ERROR, "fencing this node because it is " 143 "connected to a half-quorum of %u out of %u " 144 "nodes which doesn't include the lowest active " 145 "node %u\n", quorum, qs->qs_heartbeating, 146 lowest_hb); 147 fence = 1; 148 } 149 } 150 151 out: 152 spin_unlock(&qs->qs_lock); 153 if (fence) 154 o2quo_fence_self(); 155 } 156 157 static void o2quo_set_hold(struct o2quo_state *qs, u8 node) 158 { 159 assert_spin_locked(&qs->qs_lock); 160 161 if (!test_and_set_bit(node, qs->qs_hold_bm)) { 162 qs->qs_holds++; 163 mlog_bug_on_msg(qs->qs_holds == O2NM_MAX_NODES, 164 "node %u\n", node); 165 mlog(0, "node %u, %d total\n", node, qs->qs_holds); 166 } 167 } 168 169 static void o2quo_clear_hold(struct o2quo_state *qs, u8 node) 170 { 171 assert_spin_locked(&qs->qs_lock); 172 173 if (test_and_clear_bit(node, qs->qs_hold_bm)) { 174 mlog(0, "node %u, %d total\n", node, qs->qs_holds - 1); 175 if (--qs->qs_holds == 0) { 176 if (qs->qs_pending) { 177 qs->qs_pending = 0; 178 schedule_work(&qs->qs_work); 179 } 180 } 181 mlog_bug_on_msg(qs->qs_holds < 0, "node %u, holds %d\n", 182 node, qs->qs_holds); 183 } 184 } 185 186 /* as a node comes up we delay the quorum decision until we know the fate of 187 * the connection. the hold will be droped in conn_up or hb_down. it might be 188 * perpetuated by con_err until hb_down. if we already have a conn, we might 189 * be dropping a hold that conn_up got. */ 190 void o2quo_hb_up(u8 node) 191 { 192 struct o2quo_state *qs = &o2quo_state; 193 194 spin_lock(&qs->qs_lock); 195 196 qs->qs_heartbeating++; 197 mlog_bug_on_msg(qs->qs_heartbeating == O2NM_MAX_NODES, 198 "node %u\n", node); 199 mlog_bug_on_msg(test_bit(node, qs->qs_hb_bm), "node %u\n", node); 200 set_bit(node, qs->qs_hb_bm); 201 202 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating); 203 204 if (!test_bit(node, qs->qs_conn_bm)) 205 o2quo_set_hold(qs, node); 206 else 207 o2quo_clear_hold(qs, node); 208 209 spin_unlock(&qs->qs_lock); 210 } 211 212 /* hb going down releases any holds we might have had due to this node from 213 * conn_up, conn_err, or hb_up */ 214 void o2quo_hb_down(u8 node) 215 { 216 struct o2quo_state *qs = &o2quo_state; 217 218 spin_lock(&qs->qs_lock); 219 220 qs->qs_heartbeating--; 221 mlog_bug_on_msg(qs->qs_heartbeating < 0, 222 "node %u, %d heartbeating\n", 223 node, qs->qs_heartbeating); 224 mlog_bug_on_msg(!test_bit(node, qs->qs_hb_bm), "node %u\n", node); 225 clear_bit(node, qs->qs_hb_bm); 226 227 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating); 228 229 o2quo_clear_hold(qs, node); 230 231 spin_unlock(&qs->qs_lock); 232 } 233 234 /* this tells us that we've decided that the node is still heartbeating 235 * even though we've lost it's conn. it must only be called after conn_err 236 * and indicates that we must now make a quorum decision in the future, 237 * though we might be doing so after waiting for holds to drain. Here 238 * we'll be dropping the hold from conn_err. */ 239 void o2quo_hb_still_up(u8 node) 240 { 241 struct o2quo_state *qs = &o2quo_state; 242 243 spin_lock(&qs->qs_lock); 244 245 mlog(0, "node %u\n", node); 246 247 qs->qs_pending = 1; 248 o2quo_clear_hold(qs, node); 249 250 spin_unlock(&qs->qs_lock); 251 } 252 253 /* This is analagous to hb_up. as a node's connection comes up we delay the 254 * quorum decision until we see it heartbeating. the hold will be droped in 255 * hb_up or hb_down. it might be perpetuated by con_err until hb_down. if 256 * it's already heartbeating we we might be dropping a hold that conn_up got. 257 * */ 258 void o2quo_conn_up(u8 node) 259 { 260 struct o2quo_state *qs = &o2quo_state; 261 262 spin_lock(&qs->qs_lock); 263 264 qs->qs_connected++; 265 mlog_bug_on_msg(qs->qs_connected == O2NM_MAX_NODES, 266 "node %u\n", node); 267 mlog_bug_on_msg(test_bit(node, qs->qs_conn_bm), "node %u\n", node); 268 set_bit(node, qs->qs_conn_bm); 269 270 mlog(0, "node %u, %d total\n", node, qs->qs_connected); 271 272 if (!test_bit(node, qs->qs_hb_bm)) 273 o2quo_set_hold(qs, node); 274 else 275 o2quo_clear_hold(qs, node); 276 277 spin_unlock(&qs->qs_lock); 278 } 279 280 /* we've decided that we won't ever be connecting to the node again. if it's 281 * still heartbeating we grab a hold that will delay decisions until either the 282 * node stops heartbeating from hb_down or the caller decides that the node is 283 * still up and calls still_up */ 284 void o2quo_conn_err(u8 node) 285 { 286 struct o2quo_state *qs = &o2quo_state; 287 288 spin_lock(&qs->qs_lock); 289 290 if (test_bit(node, qs->qs_conn_bm)) { 291 qs->qs_connected--; 292 mlog_bug_on_msg(qs->qs_connected < 0, 293 "node %u, connected %d\n", 294 node, qs->qs_connected); 295 296 clear_bit(node, qs->qs_conn_bm); 297 } 298 299 mlog(0, "node %u, %d total\n", node, qs->qs_connected); 300 301 if (test_bit(node, qs->qs_hb_bm)) 302 o2quo_set_hold(qs, node); 303 304 spin_unlock(&qs->qs_lock); 305 } 306 307 void o2quo_init(void) 308 { 309 struct o2quo_state *qs = &o2quo_state; 310 311 spin_lock_init(&qs->qs_lock); 312 INIT_WORK(&qs->qs_work, o2quo_make_decision); 313 } 314 315 void o2quo_exit(void) 316 { 317 flush_scheduled_work(); 318 } 319