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/workqueue.h> 48 #include <linux/reboot.h> 49 50 #include "heartbeat.h" 51 #include "nodemanager.h" 52 #define MLOG_MASK_PREFIX ML_QUORUM 53 #include "masklog.h" 54 #include "quorum.h" 55 56 static struct o2quo_state { 57 spinlock_t qs_lock; 58 struct work_struct qs_work; 59 int qs_pending; 60 int qs_heartbeating; 61 unsigned long qs_hb_bm[BITS_TO_LONGS(O2NM_MAX_NODES)]; 62 int qs_connected; 63 unsigned long qs_conn_bm[BITS_TO_LONGS(O2NM_MAX_NODES)]; 64 int qs_holds; 65 unsigned long qs_hold_bm[BITS_TO_LONGS(O2NM_MAX_NODES)]; 66 } o2quo_state; 67 68 /* this is horribly heavy-handed. It should instead flip the file 69 * system RO and call some userspace script. */ 70 static void o2quo_fence_self(void) 71 { 72 /* panic spins with interrupts enabled. with preempt 73 * threads can still schedule, etc, etc */ 74 o2hb_stop_all_regions(); 75 76 switch (o2nm_single_cluster->cl_fence_method) { 77 case O2NM_FENCE_PANIC: 78 panic("*** ocfs2 is very sorry to be fencing this system by " 79 "panicing ***\n"); 80 break; 81 default: 82 WARN_ON(o2nm_single_cluster->cl_fence_method >= 83 O2NM_FENCE_METHODS); 84 case O2NM_FENCE_RESET: 85 printk(KERN_ERR "*** ocfs2 is very sorry to be fencing this " 86 "system by restarting ***\n"); 87 emergency_restart(); 88 break; 89 }; 90 } 91 92 /* Indicate that a timeout occurred on a hearbeat region write. The 93 * other nodes in the cluster may consider us dead at that time so we 94 * want to "fence" ourselves so that we don't scribble on the disk 95 * after they think they've recovered us. This can't solve all 96 * problems related to writeout after recovery but this hack can at 97 * least close some of those gaps. When we have real fencing, this can 98 * go away as our node would be fenced externally before other nodes 99 * begin recovery. */ 100 void o2quo_disk_timeout(void) 101 { 102 o2quo_fence_self(); 103 } 104 105 static void o2quo_make_decision(struct work_struct *work) 106 { 107 int quorum; 108 int lowest_hb, lowest_reachable = 0, fence = 0; 109 struct o2quo_state *qs = &o2quo_state; 110 111 spin_lock(&qs->qs_lock); 112 113 lowest_hb = find_first_bit(qs->qs_hb_bm, O2NM_MAX_NODES); 114 if (lowest_hb != O2NM_MAX_NODES) 115 lowest_reachable = test_bit(lowest_hb, qs->qs_conn_bm); 116 117 mlog(0, "heartbeating: %d, connected: %d, " 118 "lowest: %d (%sreachable)\n", qs->qs_heartbeating, 119 qs->qs_connected, lowest_hb, lowest_reachable ? "" : "un"); 120 121 if (!test_bit(o2nm_this_node(), qs->qs_hb_bm) || 122 qs->qs_heartbeating == 1) 123 goto out; 124 125 if (qs->qs_heartbeating & 1) { 126 /* the odd numbered cluster case is straight forward -- 127 * if we can't talk to the majority we're hosed */ 128 quorum = (qs->qs_heartbeating + 1)/2; 129 if (qs->qs_connected < quorum) { 130 mlog(ML_ERROR, "fencing this node because it is " 131 "only connected to %u nodes and %u is needed " 132 "to make a quorum out of %u heartbeating nodes\n", 133 qs->qs_connected, quorum, 134 qs->qs_heartbeating); 135 fence = 1; 136 } 137 } else { 138 /* the even numbered cluster adds the possibility of each half 139 * of the cluster being able to talk amongst themselves.. in 140 * that case we're hosed if we can't talk to the group that has 141 * the lowest numbered node */ 142 quorum = qs->qs_heartbeating / 2; 143 if (qs->qs_connected < quorum) { 144 mlog(ML_ERROR, "fencing this node because it is " 145 "only connected to %u nodes and %u is needed " 146 "to make a quorum out of %u heartbeating nodes\n", 147 qs->qs_connected, quorum, 148 qs->qs_heartbeating); 149 fence = 1; 150 } 151 else if ((qs->qs_connected == quorum) && 152 !lowest_reachable) { 153 mlog(ML_ERROR, "fencing this node because it is " 154 "connected to a half-quorum of %u out of %u " 155 "nodes which doesn't include the lowest active " 156 "node %u\n", quorum, qs->qs_heartbeating, 157 lowest_hb); 158 fence = 1; 159 } 160 } 161 162 out: 163 if (fence) { 164 spin_unlock(&qs->qs_lock); 165 o2quo_fence_self(); 166 } else { 167 mlog(ML_NOTICE, "not fencing this node, heartbeating: %d, " 168 "connected: %d, lowest: %d (%sreachable)\n", 169 qs->qs_heartbeating, qs->qs_connected, lowest_hb, 170 lowest_reachable ? "" : "un"); 171 spin_unlock(&qs->qs_lock); 172 173 } 174 175 } 176 177 static void o2quo_set_hold(struct o2quo_state *qs, u8 node) 178 { 179 assert_spin_locked(&qs->qs_lock); 180 181 if (!test_and_set_bit(node, qs->qs_hold_bm)) { 182 qs->qs_holds++; 183 mlog_bug_on_msg(qs->qs_holds == O2NM_MAX_NODES, 184 "node %u\n", node); 185 mlog(0, "node %u, %d total\n", node, qs->qs_holds); 186 } 187 } 188 189 static void o2quo_clear_hold(struct o2quo_state *qs, u8 node) 190 { 191 assert_spin_locked(&qs->qs_lock); 192 193 if (test_and_clear_bit(node, qs->qs_hold_bm)) { 194 mlog(0, "node %u, %d total\n", node, qs->qs_holds - 1); 195 if (--qs->qs_holds == 0) { 196 if (qs->qs_pending) { 197 qs->qs_pending = 0; 198 schedule_work(&qs->qs_work); 199 } 200 } 201 mlog_bug_on_msg(qs->qs_holds < 0, "node %u, holds %d\n", 202 node, qs->qs_holds); 203 } 204 } 205 206 /* as a node comes up we delay the quorum decision until we know the fate of 207 * the connection. the hold will be droped in conn_up or hb_down. it might be 208 * perpetuated by con_err until hb_down. if we already have a conn, we might 209 * be dropping a hold that conn_up got. */ 210 void o2quo_hb_up(u8 node) 211 { 212 struct o2quo_state *qs = &o2quo_state; 213 214 spin_lock(&qs->qs_lock); 215 216 qs->qs_heartbeating++; 217 mlog_bug_on_msg(qs->qs_heartbeating == O2NM_MAX_NODES, 218 "node %u\n", node); 219 mlog_bug_on_msg(test_bit(node, qs->qs_hb_bm), "node %u\n", node); 220 set_bit(node, qs->qs_hb_bm); 221 222 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating); 223 224 if (!test_bit(node, qs->qs_conn_bm)) 225 o2quo_set_hold(qs, node); 226 else 227 o2quo_clear_hold(qs, node); 228 229 spin_unlock(&qs->qs_lock); 230 } 231 232 /* hb going down releases any holds we might have had due to this node from 233 * conn_up, conn_err, or hb_up */ 234 void o2quo_hb_down(u8 node) 235 { 236 struct o2quo_state *qs = &o2quo_state; 237 238 spin_lock(&qs->qs_lock); 239 240 qs->qs_heartbeating--; 241 mlog_bug_on_msg(qs->qs_heartbeating < 0, 242 "node %u, %d heartbeating\n", 243 node, qs->qs_heartbeating); 244 mlog_bug_on_msg(!test_bit(node, qs->qs_hb_bm), "node %u\n", node); 245 clear_bit(node, qs->qs_hb_bm); 246 247 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating); 248 249 o2quo_clear_hold(qs, node); 250 251 spin_unlock(&qs->qs_lock); 252 } 253 254 /* this tells us that we've decided that the node is still heartbeating 255 * even though we've lost it's conn. it must only be called after conn_err 256 * and indicates that we must now make a quorum decision in the future, 257 * though we might be doing so after waiting for holds to drain. Here 258 * we'll be dropping the hold from conn_err. */ 259 void o2quo_hb_still_up(u8 node) 260 { 261 struct o2quo_state *qs = &o2quo_state; 262 263 spin_lock(&qs->qs_lock); 264 265 mlog(0, "node %u\n", node); 266 267 qs->qs_pending = 1; 268 o2quo_clear_hold(qs, node); 269 270 spin_unlock(&qs->qs_lock); 271 } 272 273 /* This is analogous to hb_up. as a node's connection comes up we delay the 274 * quorum decision until we see it heartbeating. the hold will be droped in 275 * hb_up or hb_down. it might be perpetuated by con_err until hb_down. if 276 * it's already heartbeating we might be dropping a hold that conn_up got. 277 * */ 278 void o2quo_conn_up(u8 node) 279 { 280 struct o2quo_state *qs = &o2quo_state; 281 282 spin_lock(&qs->qs_lock); 283 284 qs->qs_connected++; 285 mlog_bug_on_msg(qs->qs_connected == O2NM_MAX_NODES, 286 "node %u\n", node); 287 mlog_bug_on_msg(test_bit(node, qs->qs_conn_bm), "node %u\n", node); 288 set_bit(node, qs->qs_conn_bm); 289 290 mlog(0, "node %u, %d total\n", node, qs->qs_connected); 291 292 if (!test_bit(node, qs->qs_hb_bm)) 293 o2quo_set_hold(qs, node); 294 else 295 o2quo_clear_hold(qs, node); 296 297 spin_unlock(&qs->qs_lock); 298 } 299 300 /* we've decided that we won't ever be connecting to the node again. if it's 301 * still heartbeating we grab a hold that will delay decisions until either the 302 * node stops heartbeating from hb_down or the caller decides that the node is 303 * still up and calls still_up */ 304 void o2quo_conn_err(u8 node) 305 { 306 struct o2quo_state *qs = &o2quo_state; 307 308 spin_lock(&qs->qs_lock); 309 310 if (test_bit(node, qs->qs_conn_bm)) { 311 qs->qs_connected--; 312 mlog_bug_on_msg(qs->qs_connected < 0, 313 "node %u, connected %d\n", 314 node, qs->qs_connected); 315 316 clear_bit(node, qs->qs_conn_bm); 317 } 318 319 mlog(0, "node %u, %d total\n", node, qs->qs_connected); 320 321 if (test_bit(node, qs->qs_hb_bm)) 322 o2quo_set_hold(qs, node); 323 324 spin_unlock(&qs->qs_lock); 325 } 326 327 void o2quo_init(void) 328 { 329 struct o2quo_state *qs = &o2quo_state; 330 331 spin_lock_init(&qs->qs_lock); 332 INIT_WORK(&qs->qs_work, o2quo_make_decision); 333 } 334 335 void o2quo_exit(void) 336 { 337 struct o2quo_state *qs = &o2quo_state; 338 339 flush_work(&qs->qs_work); 340 } 341