summaryrefslogtreecommitdiff
path: root/fs/ocfs2/cluster/quorum.c
blob: cea739be77c466be3989c57268860c11cce285fa (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
// SPDX-License-Identifier: GPL-2.0-or-later
/* -*- mode: c; c-basic-offset: 8; -*-
 *
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * Copyright (C) 2005 Oracle.  All rights reserved.
 */

/* 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/workqueue.h>
#include <linux/reboot.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();

	switch (o2nm_single_cluster->cl_fence_method) {
	case O2NM_FENCE_PANIC:
		panic("*** ocfs2 is very sorry to be fencing this system by "
		      "panicing ***\n");
		break;
	default:
		WARN_ON(o2nm_single_cluster->cl_fence_method >=
			O2NM_FENCE_METHODS);
		fallthrough;
	case O2NM_FENCE_RESET:
		printk(KERN_ERR "*** ocfs2 is very sorry to be fencing this "
		       "system by restarting ***\n");
		emergency_restart();
		break;
	}
}

/* Indicate that a timeout occurred on a heartbeat 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:
	if (fence) {
		spin_unlock(&qs->qs_lock);
		o2quo_fence_self();
	} else {
		mlog(ML_NOTICE, "not fencing this node, heartbeating: %d, "
			"connected: %d, lowest: %d (%sreachable)\n",
			qs->qs_heartbeating, qs->qs_connected, lowest_hb,
			lowest_reachable ? "" : "un");
		spin_unlock(&qs->qs_lock);

	}

}

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 analogous 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 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);

		if (test_bit(node, qs->qs_hb_bm))
			o2quo_set_hold(qs, node);
	}

	mlog(0, "node %u, %d total\n", node, qs->qs_connected);


	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)
{
	struct o2quo_state *qs = &o2quo_state;

	flush_work(&qs->qs_work);
}