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