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 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 panic("ocfs2 is very sorry to be fencing this system by panicing\n"); 76 } 77 78 /* Indicate that a timeout occured on a hearbeat region write. The 79 * other nodes in the cluster may consider us dead at that time so we 80 * want to "fence" ourselves so that we don't scribble on the disk 81 * after they think they've recovered us. This can't solve all 82 * problems related to writeout after recovery but this hack can at 83 * least close some of those gaps. When we have real fencing, this can 84 * go away as our node would be fenced externally before other nodes 85 * begin recovery. */ 86 void o2quo_disk_timeout(void) 87 { 88 o2quo_fence_self(); 89 } 90 91 static void o2quo_make_decision(void *arg) 92 { 93 int quorum; 94 int lowest_hb, lowest_reachable = 0, fence = 0; 95 struct o2quo_state *qs = &o2quo_state; 96 97 spin_lock(&qs->qs_lock); 98 99 lowest_hb = find_first_bit(qs->qs_hb_bm, O2NM_MAX_NODES); 100 if (lowest_hb != O2NM_MAX_NODES) 101 lowest_reachable = test_bit(lowest_hb, qs->qs_conn_bm); 102 103 mlog(0, "heartbeating: %d, connected: %d, " 104 "lowest: %d (%sreachable)\n", qs->qs_heartbeating, 105 qs->qs_connected, lowest_hb, lowest_reachable ? "" : "un"); 106 107 if (!test_bit(o2nm_this_node(), qs->qs_hb_bm) || 108 qs->qs_heartbeating == 1) 109 goto out; 110 111 if (qs->qs_heartbeating & 1) { 112 /* the odd numbered cluster case is straight forward -- 113 * if we can't talk to the majority we're hosed */ 114 quorum = (qs->qs_heartbeating + 1)/2; 115 if (qs->qs_connected < quorum) { 116 mlog(ML_ERROR, "fencing this node because it is " 117 "only connected to %u nodes and %u is needed " 118 "to make a quorum out of %u heartbeating nodes\n", 119 qs->qs_connected, quorum, 120 qs->qs_heartbeating); 121 fence = 1; 122 } 123 } else { 124 /* the even numbered cluster adds the possibility of each half 125 * of the cluster being able to talk amongst themselves.. in 126 * that case we're hosed if we can't talk to the group that has 127 * the lowest numbered node */ 128 quorum = qs->qs_heartbeating / 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 if ((qs->qs_connected == quorum) && 138 !lowest_reachable) { 139 mlog(ML_ERROR, "fencing this node because it is " 140 "connected to a half-quorum of %u out of %u " 141 "nodes which doesn't include the lowest active " 142 "node %u\n", quorum, qs->qs_heartbeating, 143 lowest_hb); 144 fence = 1; 145 } 146 } 147 148 out: 149 spin_unlock(&qs->qs_lock); 150 if (fence) 151 o2quo_fence_self(); 152 } 153 154 static void o2quo_set_hold(struct o2quo_state *qs, u8 node) 155 { 156 assert_spin_locked(&qs->qs_lock); 157 158 if (!test_and_set_bit(node, qs->qs_hold_bm)) { 159 qs->qs_holds++; 160 mlog_bug_on_msg(qs->qs_holds == O2NM_MAX_NODES, 161 "node %u\n", node); 162 mlog(0, "node %u, %d total\n", node, qs->qs_holds); 163 } 164 } 165 166 static void o2quo_clear_hold(struct o2quo_state *qs, u8 node) 167 { 168 assert_spin_locked(&qs->qs_lock); 169 170 if (test_and_clear_bit(node, qs->qs_hold_bm)) { 171 mlog(0, "node %u, %d total\n", node, qs->qs_holds - 1); 172 if (--qs->qs_holds == 0) { 173 if (qs->qs_pending) { 174 qs->qs_pending = 0; 175 schedule_work(&qs->qs_work); 176 } 177 } 178 mlog_bug_on_msg(qs->qs_holds < 0, "node %u, holds %d\n", 179 node, qs->qs_holds); 180 } 181 } 182 183 /* as a node comes up we delay the quorum decision until we know the fate of 184 * the connection. the hold will be droped in conn_up or hb_down. it might be 185 * perpetuated by con_err until hb_down. if we already have a conn, we might 186 * be dropping a hold that conn_up got. */ 187 void o2quo_hb_up(u8 node) 188 { 189 struct o2quo_state *qs = &o2quo_state; 190 191 spin_lock(&qs->qs_lock); 192 193 qs->qs_heartbeating++; 194 mlog_bug_on_msg(qs->qs_heartbeating == O2NM_MAX_NODES, 195 "node %u\n", node); 196 mlog_bug_on_msg(test_bit(node, qs->qs_hb_bm), "node %u\n", node); 197 set_bit(node, qs->qs_hb_bm); 198 199 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating); 200 201 if (!test_bit(node, qs->qs_conn_bm)) 202 o2quo_set_hold(qs, node); 203 else 204 o2quo_clear_hold(qs, node); 205 206 spin_unlock(&qs->qs_lock); 207 } 208 209 /* hb going down releases any holds we might have had due to this node from 210 * conn_up, conn_err, or hb_up */ 211 void o2quo_hb_down(u8 node) 212 { 213 struct o2quo_state *qs = &o2quo_state; 214 215 spin_lock(&qs->qs_lock); 216 217 qs->qs_heartbeating--; 218 mlog_bug_on_msg(qs->qs_heartbeating < 0, 219 "node %u, %d heartbeating\n", 220 node, qs->qs_heartbeating); 221 mlog_bug_on_msg(!test_bit(node, qs->qs_hb_bm), "node %u\n", node); 222 clear_bit(node, qs->qs_hb_bm); 223 224 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating); 225 226 o2quo_clear_hold(qs, node); 227 228 spin_unlock(&qs->qs_lock); 229 } 230 231 /* this tells us that we've decided that the node is still heartbeating 232 * even though we've lost it's conn. it must only be called after conn_err 233 * and indicates that we must now make a quorum decision in the future, 234 * though we might be doing so after waiting for holds to drain. Here 235 * we'll be dropping the hold from conn_err. */ 236 void o2quo_hb_still_up(u8 node) 237 { 238 struct o2quo_state *qs = &o2quo_state; 239 240 spin_lock(&qs->qs_lock); 241 242 mlog(0, "node %u\n", node); 243 244 qs->qs_pending = 1; 245 o2quo_clear_hold(qs, node); 246 247 spin_unlock(&qs->qs_lock); 248 } 249 250 /* This is analagous to hb_up. as a node's connection comes up we delay the 251 * quorum decision until we see it heartbeating. the hold will be droped in 252 * hb_up or hb_down. it might be perpetuated by con_err until hb_down. if 253 * it's already heartbeating we we might be dropping a hold that conn_up got. 254 * */ 255 void o2quo_conn_up(u8 node) 256 { 257 struct o2quo_state *qs = &o2quo_state; 258 259 spin_lock(&qs->qs_lock); 260 261 qs->qs_connected++; 262 mlog_bug_on_msg(qs->qs_connected == O2NM_MAX_NODES, 263 "node %u\n", node); 264 mlog_bug_on_msg(test_bit(node, qs->qs_conn_bm), "node %u\n", node); 265 set_bit(node, qs->qs_conn_bm); 266 267 mlog(0, "node %u, %d total\n", node, qs->qs_connected); 268 269 if (!test_bit(node, qs->qs_hb_bm)) 270 o2quo_set_hold(qs, node); 271 else 272 o2quo_clear_hold(qs, node); 273 274 spin_unlock(&qs->qs_lock); 275 } 276 277 /* we've decided that we won't ever be connecting to the node again. if it's 278 * still heartbeating we grab a hold that will delay decisions until either the 279 * node stops heartbeating from hb_down or the caller decides that the node is 280 * still up and calls still_up */ 281 void o2quo_conn_err(u8 node) 282 { 283 struct o2quo_state *qs = &o2quo_state; 284 285 spin_lock(&qs->qs_lock); 286 287 if (test_bit(node, qs->qs_conn_bm)) { 288 qs->qs_connected--; 289 mlog_bug_on_msg(qs->qs_connected < 0, 290 "node %u, connected %d\n", 291 node, qs->qs_connected); 292 293 clear_bit(node, qs->qs_conn_bm); 294 } 295 296 mlog(0, "node %u, %d total\n", node, qs->qs_connected); 297 298 if (test_bit(node, qs->qs_hb_bm)) 299 o2quo_set_hold(qs, node); 300 301 spin_unlock(&qs->qs_lock); 302 } 303 304 void o2quo_init(void) 305 { 306 struct o2quo_state *qs = &o2quo_state; 307 308 spin_lock_init(&qs->qs_lock); 309 INIT_WORK(&qs->qs_work, o2quo_make_decision, NULL); 310 } 311 312 void o2quo_exit(void) 313 { 314 flush_scheduled_work(); 315 } 316