xref: /illumos-gate/usr/src/uts/common/fs/zfs/mmp.c (revision 4348eb901228d2f8fa50bb132a34248e8662074e)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
23  * Copyright 2019 Joyent, Inc.
24  */
25 
26 #include <sys/abd.h>
27 #include <sys/mmp.h>
28 #include <sys/spa.h>
29 #include <sys/spa_impl.h>
30 #include <sys/time.h>
31 #include <sys/vdev.h>
32 #include <sys/vdev_impl.h>
33 #include <sys/zfs_context.h>
34 #include <sys/callb.h>
35 
36 /*
37  * Multi-Modifier Protection (MMP) attempts to prevent a user from importing
38  * or opening a pool on more than one host at a time.  In particular, it
39  * prevents "zpool import -f" on a host from succeeding while the pool is
40  * already imported on another host.  There are many other ways in which a
41  * device could be used by two hosts for different purposes at the same time
42  * resulting in pool damage.  This implementation does not attempt to detect
43  * those cases.
44  *
45  * MMP operates by ensuring there are frequent visible changes on disk (a
46  * "heartbeat") at all times.  And by altering the import process to check
47  * for these changes and failing the import when they are detected.  This
48  * functionality is enabled by setting the 'multihost' pool property to on.
49  *
50  * Uberblocks written by the txg_sync thread always go into the first
51  * (N-MMP_BLOCKS_PER_LABEL) slots, the remaining slots are reserved for MMP.
52  * They are used to hold uberblocks which are exactly the same as the last
53  * synced uberblock except that the ub_timestamp and mmp_config are frequently
54  * updated.  Like all other uberblocks, the slot is written with an embedded
55  * checksum, and slots with invalid checksums are ignored.  This provides the
56  * "heartbeat", with no risk of overwriting good uberblocks that must be
57  * preserved, e.g. previous txgs and associated block pointers.
58  *
59  * Three optional fields are added to uberblock structure; ub_mmp_magic,
60  * ub_mmp_config, and ub_mmp_delay.  The ub_mmp_magic value allows zfs to tell
61  * whether the other ub_mmp_* fields are valid.  The ub_mmp_config field tells
62  * the importing host the settings of zfs_multihost_interval and
63  * zfs_multihost_fail_intervals on the host which last had (or currently has)
64  * the pool imported.  These determine how long a host must wait to detect
65  * activity in the pool, before concluding the pool is not in use.  The
66  * mmp_delay field is a decaying average of the amount of time between
67  * completion of successive MMP writes, in nanoseconds.  It indicates whether
68  * MMP is enabled.
69  *
70  * During import an activity test may now be performed to determine if
71  * the pool is in use.  The activity test is typically required if the
72  * ZPOOL_CONFIG_HOSTID does not match the system hostid, the pool state is
73  * POOL_STATE_ACTIVE, and the pool is not a root pool.
74  *
75  * The activity test finds the "best" uberblock (highest txg, timestamp, and, if
76  * ub_mmp_magic is valid, sequence number from ub_mmp_config).  It then waits
77  * some time, and finds the "best" uberblock again.  If any of the mentioned
78  * fields have different values in the newly read uberblock, the pool is in use
79  * by another host and the import fails.  In order to assure the accuracy of the
80  * activity test, the default values result in an activity test duration of 20x
81  * the mmp write interval.
82  *
83  * The duration of the "zpool import" activity test depends on the information
84  * available in the "best" uberblock:
85  *
86  * 1) If uberblock was written by zfs-0.8 or newer and fail_intervals > 0:
87  *    ub_mmp_config.fail_intervals * ub_mmp_config.multihost_interval * 2
88  *
89  *    In this case, a weak guarantee is provided.  Since the host which last had
90  *    the pool imported will suspend the pool if no mmp writes land within
91  *    fail_intervals * multihost_interval ms, the absence of writes during that
92  *    time means either the pool is not imported, or it is imported but the pool
93  *    is suspended and no further writes will occur.
94  *
95  *    Note that resuming the suspended pool on the remote host would invalidate
96  *    this guarantee, and so it is not allowed.
97  *
98  *    The factor of 2 provides a conservative safety factor and derives from
99  *    MMP_IMPORT_SAFETY_FACTOR;
100  *
101  * 2) If uberblock was written by zfs-0.8 or newer and fail_intervals == 0:
102  *    (ub_mmp_config.multihost_interval + ub_mmp_delay) *
103  *        zfs_multihost_import_intervals
104  *
105  *    In this case no guarantee can provided.  However, as long as some devices
106  *    are healthy and connected, it is likely that at least one write will land
107  *    within (multihost_interval + mmp_delay) because multihost_interval is
108  *    enough time for a write to be attempted to each leaf vdev, and mmp_delay
109  *    is enough for one to land, based on past delays.  Multiplying by
110  *    zfs_multihost_import_intervals provides a conservative safety factor.
111  *
112  * 3) If uberblock was written by zfs-0.7:
113  *    (zfs_multihost_interval + ub_mmp_delay) * zfs_multihost_import_intervals
114  *
115  *    The same logic as case #2 applies, but we do not know remote tunables.
116  *
117  *    We use the local value for zfs_multihost_interval because the original MMP
118  *    did not record this value in the uberblock.
119  *
120  *    ub_mmp_delay >= (zfs_multihost_interval / leaves), so if the other host
121  *    has a much larger zfs_multihost_interval set, ub_mmp_delay will reflect
122  *    that.  We will have waited enough time for zfs_multihost_import_intervals
123  *    writes to be issued and all but one to land.
124  *
125  *    single device pool example delays
126  *
127  *    import_delay = (1 + 1) * 20   =  40s #defaults, no I/O delay
128  *    import_delay = (1 + 10) * 20  = 220s #defaults, 10s I/O delay
129  *    import_delay = (10 + 10) * 20 = 400s #10s multihost_interval,
130  *                                          no I/O delay
131  *    100 device pool example delays
132  *
133  *    import_delay = (1 + .01) * 20 =  20s #defaults, no I/O delay
134  *    import_delay = (1 + 10) * 20  = 220s #defaults, 10s I/O delay
135  *    import_delay = (10 + .1) * 20 = 202s #10s multihost_interval,
136  *                                          no I/O delay
137  *
138  * 4) Otherwise, this uberblock was written by a pre-MMP zfs:
139  *    zfs_multihost_import_intervals * zfs_multihost_interval
140  *
141  *    In this case local tunables are used.  By default this product = 10s, long
142  *    enough for a pool with any activity at all to write at least one
143  *    uberblock.  No guarantee can be provided.
144  *
145  * Additionally, the duration is then extended by a random 25% to attempt to to
146  * detect simultaneous imports.  For example, if both partner hosts are rebooted
147  * at the same time and automatically attempt to import the pool.
148  */
149 
150 /*
151  * Used to control the frequency of mmp writes which are performed when the
152  * 'multihost' pool property is on.  This is one factor used to determine the
153  * length of the activity check during import.
154  *
155  * On average an mmp write will be issued for each leaf vdev every
156  * zfs_multihost_interval milliseconds.  In practice, the observed period can
157  * vary with the I/O load and this observed value is the ub_mmp_delay which is
158  * stored in the uberblock.  The minimum allowed value is 100 ms.
159  */
160 ulong_t zfs_multihost_interval = MMP_DEFAULT_INTERVAL;
161 
162 /*
163  * Used to control the duration of the activity test on import.  Smaller values
164  * of zfs_multihost_import_intervals will reduce the import time but increase
165  * the risk of failing to detect an active pool.  The total activity check time
166  * is never allowed to drop below one second.  A value of 0 is ignored and
167  * treated as if it was set to 1.
168  */
169 uint_t zfs_multihost_import_intervals = MMP_DEFAULT_IMPORT_INTERVALS;
170 
171 /*
172  * Controls the behavior of the pool when mmp write failures or delays are
173  * detected.
174  *
175  * When zfs_multihost_fail_intervals = 0, mmp write failures or delays are
176  * ignored.  The failures will still be reported to the ZED which depending on
177  * its configuration may take action such as suspending the pool or taking a
178  * device offline.
179  *
180  * When zfs_multihost_fail_intervals > 0, the pool will be suspended if
181  * zfs_multihost_fail_intervals * zfs_multihost_interval milliseconds pass
182  * without a successful mmp write.  This guarantees the activity test will see
183  * mmp writes if the pool is imported.  A value of 1 is ignored and treated as
184  * if it was set to 2, because a single leaf vdev pool will issue a write once
185  * per multihost_interval and thus any variation in latency would cause the
186  * pool to be suspended.
187  */
188 uint_t zfs_multihost_fail_intervals = MMP_DEFAULT_FAIL_INTERVALS;
189 
190 char *mmp_tag = "mmp_write_uberblock";
191 static void mmp_thread(void *arg);
192 
193 void
mmp_init(spa_t * spa)194 mmp_init(spa_t *spa)
195 {
196 	mmp_thread_t *mmp = &spa->spa_mmp;
197 
198 	mutex_init(&mmp->mmp_thread_lock, NULL, MUTEX_DEFAULT, NULL);
199 	cv_init(&mmp->mmp_thread_cv, NULL, CV_DEFAULT, NULL);
200 	mutex_init(&mmp->mmp_io_lock, NULL, MUTEX_DEFAULT, NULL);
201 	mmp->mmp_kstat_id = 1;
202 
203 	/*
204 	 * mmp_write_done() calculates mmp_delay based on prior mmp_delay and
205 	 * the elapsed time since the last write.  For the first mmp write,
206 	 * there is no "last write", so we start with fake non-zero values.
207 	 */
208 	mmp->mmp_last_write = gethrtime();
209 	mmp->mmp_delay = MSEC2NSEC(MMP_INTERVAL_OK(zfs_multihost_interval));
210 }
211 
212 void
mmp_fini(spa_t * spa)213 mmp_fini(spa_t *spa)
214 {
215 	mmp_thread_t *mmp = &spa->spa_mmp;
216 
217 	mutex_destroy(&mmp->mmp_thread_lock);
218 	cv_destroy(&mmp->mmp_thread_cv);
219 	mutex_destroy(&mmp->mmp_io_lock);
220 }
221 
222 static void
mmp_thread_enter(mmp_thread_t * mmp,callb_cpr_t * cpr)223 mmp_thread_enter(mmp_thread_t *mmp, callb_cpr_t *cpr)
224 {
225 	CALLB_CPR_INIT(cpr, &mmp->mmp_thread_lock, callb_generic_cpr, FTAG);
226 	mutex_enter(&mmp->mmp_thread_lock);
227 }
228 
229 static void
mmp_thread_exit(mmp_thread_t * mmp,kthread_t ** mpp,callb_cpr_t * cpr)230 mmp_thread_exit(mmp_thread_t *mmp, kthread_t **mpp, callb_cpr_t *cpr)
231 {
232 	ASSERT(*mpp != NULL);
233 	*mpp = NULL;
234 	cv_broadcast(&mmp->mmp_thread_cv);
235 	CALLB_CPR_EXIT(cpr);		/* drops &mmp->mmp_thread_lock */
236 	thread_exit();
237 }
238 
239 void
mmp_thread_start(spa_t * spa)240 mmp_thread_start(spa_t *spa)
241 {
242 	mmp_thread_t *mmp = &spa->spa_mmp;
243 
244 	if (spa_writeable(spa)) {
245 		mutex_enter(&mmp->mmp_thread_lock);
246 		if (!mmp->mmp_thread) {
247 			mmp->mmp_thread = thread_create(NULL, 0, mmp_thread,
248 			    spa, 0, &p0, TS_RUN, minclsyspri);
249 			zfs_dbgmsg("MMP thread started pool '%s' "
250 			    "gethrtime %llu", spa_name(spa), gethrtime());
251 		}
252 		mutex_exit(&mmp->mmp_thread_lock);
253 	}
254 }
255 
256 void
mmp_thread_stop(spa_t * spa)257 mmp_thread_stop(spa_t *spa)
258 {
259 	mmp_thread_t *mmp = &spa->spa_mmp;
260 
261 	mutex_enter(&mmp->mmp_thread_lock);
262 	mmp->mmp_thread_exiting = 1;
263 	cv_broadcast(&mmp->mmp_thread_cv);
264 
265 	while (mmp->mmp_thread) {
266 		cv_wait(&mmp->mmp_thread_cv, &mmp->mmp_thread_lock);
267 	}
268 	mutex_exit(&mmp->mmp_thread_lock);
269 	zfs_dbgmsg("MMP thread stopped pool '%s' gethrtime %llu",
270 	    spa_name(spa), gethrtime());
271 
272 	ASSERT(mmp->mmp_thread == NULL);
273 	mmp->mmp_thread_exiting = 0;
274 }
275 
276 typedef enum mmp_vdev_state_flag {
277 	MMP_FAIL_NOT_WRITABLE	= (1 << 0),
278 	MMP_FAIL_WRITE_PENDING	= (1 << 1),
279 } mmp_vdev_state_flag_t;
280 
281 /*
282  * Find a leaf vdev to write an MMP block to.  It must not have an outstanding
283  * mmp write (if so a new write will also likely block).  If there is no usable
284  * leaf, a nonzero error value is returned. The error value returned is a bit
285  * field.
286  *
287  * MMP_FAIL_WRITE_PENDING   One or more leaf vdevs are writeable, but have an
288  *                          outstanding MMP write.
289  * MMP_FAIL_NOT_WRITABLE    One or more leaf vdevs are not writeable.
290  */
291 
292 static int
mmp_next_leaf(spa_t * spa)293 mmp_next_leaf(spa_t *spa)
294 {
295 	vdev_t *leaf;
296 	vdev_t *starting_leaf;
297 	int fail_mask = 0;
298 
299 	ASSERT(MUTEX_HELD(&spa->spa_mmp.mmp_io_lock));
300 	ASSERT(spa_config_held(spa, SCL_STATE, RW_READER));
301 	ASSERT(list_link_active(&spa->spa_leaf_list.list_head) == B_TRUE);
302 	ASSERT(!list_is_empty(&spa->spa_leaf_list));
303 
304 	if (spa->spa_mmp.mmp_leaf_last_gen != spa->spa_leaf_list_gen) {
305 		spa->spa_mmp.mmp_last_leaf = list_head(&spa->spa_leaf_list);
306 		spa->spa_mmp.mmp_leaf_last_gen = spa->spa_leaf_list_gen;
307 	}
308 
309 	leaf = spa->spa_mmp.mmp_last_leaf;
310 	if (leaf == NULL)
311 		leaf = list_head(&spa->spa_leaf_list);
312 	starting_leaf = leaf;
313 
314 	do {
315 		leaf = list_next(&spa->spa_leaf_list, leaf);
316 		if (leaf == NULL)
317 			leaf = list_head(&spa->spa_leaf_list);
318 
319 		if (!vdev_writeable(leaf)) {
320 			fail_mask |= MMP_FAIL_NOT_WRITABLE;
321 		} else if (leaf->vdev_mmp_pending != 0) {
322 			fail_mask |= MMP_FAIL_WRITE_PENDING;
323 		} else {
324 			spa->spa_mmp.mmp_last_leaf = leaf;
325 			return (0);
326 		}
327 	} while (leaf != starting_leaf);
328 
329 	ASSERT(fail_mask);
330 
331 	return (fail_mask);
332 }
333 
334 /*
335  * MMP writes are issued on a fixed schedule, but may complete at variable,
336  * much longer, intervals.  The mmp_delay captures long periods between
337  * successful writes for any reason, including disk latency, scheduling delays,
338  * etc.
339  *
340  * The mmp_delay is usually calculated as a decaying average, but if the latest
341  * delay is higher we do not average it, so that we do not hide sudden spikes
342  * which the importing host must wait for.
343  *
344  * If writes are occurring frequently, such as due to a high rate of txg syncs,
345  * the mmp_delay could become very small.  Since those short delays depend on
346  * activity we cannot count on, we never allow mmp_delay to get lower than rate
347  * expected if only mmp_thread writes occur.
348  *
349  * If an mmp write was skipped or fails, and we have already waited longer than
350  * mmp_delay, we need to update it so the next write reflects the longer delay.
351  *
352  * Do not set mmp_delay if the multihost property is not on, so as not to
353  * trigger an activity check on import.
354  */
355 static void
mmp_delay_update(spa_t * spa,boolean_t write_completed)356 mmp_delay_update(spa_t *spa, boolean_t write_completed)
357 {
358 	mmp_thread_t *mts = &spa->spa_mmp;
359 	hrtime_t delay = gethrtime() - mts->mmp_last_write;
360 
361 	ASSERT(MUTEX_HELD(&mts->mmp_io_lock));
362 
363 	if (spa_multihost(spa) == B_FALSE) {
364 		mts->mmp_delay = 0;
365 		return;
366 	}
367 
368 	if (delay > mts->mmp_delay)
369 		mts->mmp_delay = delay;
370 
371 	if (write_completed == B_FALSE)
372 		return;
373 
374 	mts->mmp_last_write = gethrtime();
375 
376 	/*
377 	 * strictly less than, in case delay was changed above.
378 	 */
379 	if (delay < mts->mmp_delay) {
380 		hrtime_t min_delay =
381 		    MSEC2NSEC(MMP_INTERVAL_OK(zfs_multihost_interval)) /
382 		    MAX(1, vdev_count_leaves(spa));
383 		mts->mmp_delay = MAX(((delay + mts->mmp_delay * 127) / 128),
384 		    min_delay);
385 	}
386 }
387 
388 static void
mmp_write_done(zio_t * zio)389 mmp_write_done(zio_t *zio)
390 {
391 	spa_t *spa = zio->io_spa;
392 	vdev_t *vd = zio->io_vd;
393 	mmp_thread_t *mts = zio->io_private;
394 
395 	mutex_enter(&mts->mmp_io_lock);
396 	uint64_t mmp_kstat_id = vd->vdev_mmp_kstat_id;
397 	hrtime_t mmp_write_duration = gethrtime() - vd->vdev_mmp_pending;
398 
399 	mmp_delay_update(spa, (zio->io_error == 0));
400 
401 	vd->vdev_mmp_pending = 0;
402 	vd->vdev_mmp_kstat_id = 0;
403 
404 	mutex_exit(&mts->mmp_io_lock);
405 	spa_config_exit(spa, SCL_STATE, mmp_tag);
406 
407 	abd_free(zio->io_abd);
408 }
409 
410 /*
411  * When the uberblock on-disk is updated by a spa_sync,
412  * creating a new "best" uberblock, update the one stored
413  * in the mmp thread state, used for mmp writes.
414  */
415 void
mmp_update_uberblock(spa_t * spa,uberblock_t * ub)416 mmp_update_uberblock(spa_t *spa, uberblock_t *ub)
417 {
418 	mmp_thread_t *mmp = &spa->spa_mmp;
419 
420 	mutex_enter(&mmp->mmp_io_lock);
421 	mmp->mmp_ub = *ub;
422 	mmp->mmp_seq = 1;
423 	mmp->mmp_ub.ub_timestamp = gethrestime_sec();
424 	mmp_delay_update(spa, B_TRUE);
425 	mutex_exit(&mmp->mmp_io_lock);
426 }
427 
428 /*
429  * Choose a random vdev, label, and MMP block, and write over it
430  * with a copy of the last-synced uberblock, whose timestamp
431  * has been updated to reflect that the pool is in use.
432  */
433 static void
mmp_write_uberblock(spa_t * spa)434 mmp_write_uberblock(spa_t *spa)
435 {
436 	int flags = ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_CANFAIL;
437 	mmp_thread_t *mmp = &spa->spa_mmp;
438 	uberblock_t *ub;
439 	vdev_t *vd = NULL;
440 	int label, error;
441 	uint64_t offset;
442 
443 	hrtime_t lock_acquire_time = gethrtime();
444 	spa_config_enter(spa, SCL_STATE, mmp_tag, RW_READER);
445 	lock_acquire_time = gethrtime() - lock_acquire_time;
446 	if (lock_acquire_time > (MSEC2NSEC(MMP_MIN_INTERVAL) / 10))
447 		zfs_dbgmsg("MMP SCL_STATE acquisition pool '%s' took %llu ns "
448 		    "gethrtime %llu", spa_name(spa), lock_acquire_time,
449 		    gethrtime());
450 
451 	mutex_enter(&mmp->mmp_io_lock);
452 
453 	error = mmp_next_leaf(spa);
454 
455 	/*
456 	 * spa_mmp_history has two types of entries:
457 	 * Issued MMP write: records time issued, error status, etc.
458 	 * Skipped MMP write: an MMP write could not be issued because no
459 	 * suitable leaf vdev was available.  See comment above struct
460 	 * spa_mmp_history for details.
461 	 */
462 
463 	if (error) {
464 		mmp_delay_update(spa, B_FALSE);
465 		if (mmp->mmp_skip_error == error) {
466 			/*
467 			 * ZoL porting note: the following is TBD
468 			 * spa_mmp_history_set_skip(spa, mmp->mmp_kstat_id - 1);
469 			 */
470 		} else {
471 			mmp->mmp_skip_error = error;
472 			/*
473 			 * ZoL porting note: the following is TBD
474 			 * spa_mmp_history_add(spa, mmp->mmp_ub.ub_txg,
475 			 * gethrestime_sec(), mmp->mmp_delay, NULL, 0,
476 			 * mmp->mmp_kstat_id++, error);
477 			 */
478 			zfs_dbgmsg("MMP error choosing leaf pool '%s' "
479 			    "gethrtime %llu fail_mask %#x", spa_name(spa),
480 			    gethrtime(), error);
481 		}
482 		mutex_exit(&mmp->mmp_io_lock);
483 		spa_config_exit(spa, SCL_STATE, mmp_tag);
484 		return;
485 	}
486 
487 	vd = spa->spa_mmp.mmp_last_leaf;
488 	if (mmp->mmp_skip_error != 0) {
489 		mmp->mmp_skip_error = 0;
490 		zfs_dbgmsg("MMP write after skipping due to unavailable "
491 		    "leaves, pool '%s' gethrtime %llu leaf %#llu",
492 		    spa_name(spa), gethrtime(), vd->vdev_guid);
493 	}
494 
495 	if (mmp->mmp_zio_root == NULL)
496 		mmp->mmp_zio_root = zio_root(spa, NULL, NULL,
497 		    flags | ZIO_FLAG_GODFATHER);
498 
499 	if (mmp->mmp_ub.ub_timestamp != gethrestime_sec()) {
500 		/*
501 		 * Want to reset mmp_seq when timestamp advances because after
502 		 * an mmp_seq wrap new values will not be chosen by
503 		 * uberblock_compare() as the "best".
504 		 */
505 		mmp->mmp_ub.ub_timestamp = gethrestime_sec();
506 		mmp->mmp_seq = 1;
507 	}
508 
509 	ub = &mmp->mmp_ub;
510 	ub->ub_mmp_magic = MMP_MAGIC;
511 	ub->ub_mmp_delay = mmp->mmp_delay;
512 	ub->ub_mmp_config = MMP_SEQ_SET(mmp->mmp_seq) |
513 	    MMP_INTERVAL_SET(MMP_INTERVAL_OK(zfs_multihost_interval)) |
514 	    MMP_FAIL_INT_SET(MMP_FAIL_INTVS_OK(
515 	    zfs_multihost_fail_intervals));
516 	vd->vdev_mmp_pending = gethrtime();
517 	vd->vdev_mmp_kstat_id = mmp->mmp_kstat_id;
518 
519 	zio_t *zio  = zio_null(mmp->mmp_zio_root, spa, NULL, NULL, NULL, flags);
520 	abd_t *ub_abd = abd_alloc_for_io(VDEV_UBERBLOCK_SIZE(vd), B_TRUE);
521 	abd_zero(ub_abd, VDEV_UBERBLOCK_SIZE(vd));
522 	abd_copy_from_buf(ub_abd, ub, sizeof (uberblock_t));
523 
524 	mmp->mmp_seq++;
525 	mmp->mmp_kstat_id++;
526 	mutex_exit(&mmp->mmp_io_lock);
527 
528 	offset = VDEV_UBERBLOCK_OFFSET(vd, VDEV_UBERBLOCK_COUNT(vd) -
529 	    MMP_BLOCKS_PER_LABEL + spa_get_random(MMP_BLOCKS_PER_LABEL));
530 
531 	label = spa_get_random(VDEV_LABELS);
532 	vdev_label_write(zio, vd, label, ub_abd, offset,
533 	    VDEV_UBERBLOCK_SIZE(vd), mmp_write_done, mmp,
534 	    flags | ZIO_FLAG_DONT_PROPAGATE);
535 
536 	/*
537 	 * ZoL porting note: the following is TBD
538 	 * (void) spa_mmp_history_add(spa, ub->ub_txg, ub->ub_timestamp,
539 	 * ub->ub_mmp_delay, vd, label, vd->vdev_mmp_kstat_id, 0);
540 	 */
541 
542 	zio_nowait(zio);
543 }
544 
545 static void
mmp_thread(void * arg)546 mmp_thread(void *arg)
547 {
548 	spa_t *spa = (spa_t *)arg;
549 	mmp_thread_t *mmp = &spa->spa_mmp;
550 	boolean_t suspended = spa_suspended(spa);
551 	boolean_t multihost = spa_multihost(spa);
552 	uint64_t mmp_interval = MSEC2NSEC(MMP_INTERVAL_OK(
553 	    zfs_multihost_interval));
554 	uint32_t mmp_fail_intervals = MMP_FAIL_INTVS_OK(
555 	    zfs_multihost_fail_intervals);
556 	hrtime_t mmp_fail_ns = mmp_fail_intervals * mmp_interval;
557 	boolean_t last_spa_suspended = suspended;
558 	boolean_t last_spa_multihost = multihost;
559 	uint64_t last_mmp_interval = mmp_interval;
560 	uint32_t last_mmp_fail_intervals = mmp_fail_intervals;
561 	hrtime_t last_mmp_fail_ns = mmp_fail_ns;
562 	callb_cpr_t cpr;
563 	int skip_wait = 0;
564 
565 	mmp_thread_enter(mmp, &cpr);
566 
567 	while (!mmp->mmp_thread_exiting) {
568 		hrtime_t next_time = gethrtime() +
569 		    MSEC2NSEC(MMP_DEFAULT_INTERVAL);
570 		int leaves = MAX(vdev_count_leaves(spa), 1);
571 
572 		/* Detect changes in tunables or state */
573 
574 		last_spa_suspended = suspended;
575 		last_spa_multihost = multihost;
576 		suspended = spa_suspended(spa);
577 		multihost = spa_multihost(spa);
578 
579 		last_mmp_interval = mmp_interval;
580 		last_mmp_fail_intervals = mmp_fail_intervals;
581 		last_mmp_fail_ns = mmp_fail_ns;
582 		mmp_interval = MSEC2NSEC(MMP_INTERVAL_OK(
583 		    zfs_multihost_interval));
584 		mmp_fail_intervals = MMP_FAIL_INTVS_OK(
585 		    zfs_multihost_fail_intervals);
586 
587 		/* Smooth so pool is not suspended when reducing tunables */
588 		if (mmp_fail_intervals * mmp_interval < mmp_fail_ns) {
589 			mmp_fail_ns = (mmp_fail_ns * 31 +
590 			    mmp_fail_intervals * mmp_interval) / 32;
591 		} else {
592 			mmp_fail_ns = mmp_fail_intervals *
593 			    mmp_interval;
594 		}
595 
596 		if (mmp_interval != last_mmp_interval ||
597 		    mmp_fail_intervals != last_mmp_fail_intervals) {
598 			/*
599 			 * We want other hosts to see new tunables as quickly as
600 			 * possible.  Write out at higher frequency than usual.
601 			 */
602 			skip_wait += leaves;
603 		}
604 
605 		if (multihost)
606 			next_time = gethrtime() + mmp_interval / leaves;
607 
608 		if (mmp_fail_ns != last_mmp_fail_ns) {
609 			zfs_dbgmsg("MMP interval change pool '%s' "
610 			    "gethrtime %llu last_mmp_interval %llu "
611 			    "mmp_interval %llu last_mmp_fail_intervals %u "
612 			    "mmp_fail_intervals %u mmp_fail_ns %llu "
613 			    "skip_wait %d leaves %d next_time %llu",
614 			    spa_name(spa), gethrtime(), last_mmp_interval,
615 			    mmp_interval, last_mmp_fail_intervals,
616 			    mmp_fail_intervals, mmp_fail_ns, skip_wait, leaves,
617 			    next_time);
618 		}
619 
620 		/*
621 		 * MMP off => on, or suspended => !suspended:
622 		 * No writes occurred recently.  Update mmp_last_write to give
623 		 * us some time to try.
624 		 */
625 		if ((!last_spa_multihost && multihost) ||
626 		    (last_spa_suspended && !suspended)) {
627 			zfs_dbgmsg("MMP state change pool '%s': gethrtime %llu "
628 			    "last_spa_multihost %u multihost %u "
629 			    "last_spa_suspended %u suspended %u",
630 			    spa_name(spa), last_spa_multihost, multihost,
631 			    last_spa_suspended, suspended);
632 			mutex_enter(&mmp->mmp_io_lock);
633 			mmp->mmp_last_write = gethrtime();
634 			mmp->mmp_delay = mmp_interval;
635 			mutex_exit(&mmp->mmp_io_lock);
636 		}
637 
638 		/*
639 		 * MMP on => off:
640 		 * mmp_delay == 0 tells importing node to skip activity check.
641 		 */
642 		if (last_spa_multihost && !multihost) {
643 			mutex_enter(&mmp->mmp_io_lock);
644 			mmp->mmp_delay = 0;
645 			mutex_exit(&mmp->mmp_io_lock);
646 		}
647 
648 		/*
649 		 * Suspend the pool if no MMP write has succeeded in over
650 		 * mmp_interval * mmp_fail_intervals nanoseconds.
651 		 */
652 		if (multihost && !suspended && mmp_fail_intervals &&
653 		    (gethrtime() - mmp->mmp_last_write) > mmp_fail_ns) {
654 			zfs_dbgmsg("MMP suspending pool '%s': gethrtime %llu "
655 			    "mmp_last_write %llu mmp_interval %llu "
656 			    "mmp_fail_intervals %llu mmp_fail_ns %llu",
657 			    spa_name(spa), (u_longlong_t)gethrtime(),
658 			    (u_longlong_t)mmp->mmp_last_write,
659 			    (u_longlong_t)mmp_interval,
660 			    (u_longlong_t)mmp_fail_intervals,
661 			    (u_longlong_t)mmp_fail_ns);
662 			cmn_err(CE_WARN, "MMP writes to pool '%s' have not "
663 			    "succeeded in over %llu ms; suspending pool. "
664 			    "Hrtime %llu",
665 			    spa_name(spa),
666 			    NSEC2MSEC(gethrtime() - mmp->mmp_last_write),
667 			    gethrtime());
668 			zio_suspend(spa, NULL, ZIO_SUSPEND_MMP);
669 		}
670 
671 		if (multihost && !suspended)
672 			mmp_write_uberblock(spa);
673 
674 		if (skip_wait > 0) {
675 			next_time = gethrtime() + MSEC2NSEC(MMP_MIN_INTERVAL) /
676 			    leaves;
677 			skip_wait--;
678 		}
679 
680 		CALLB_CPR_SAFE_BEGIN(&cpr);
681 		(void) cv_timedwait_sig_hrtime(&mmp->mmp_thread_cv,
682 		    &mmp->mmp_thread_lock, next_time);
683 		CALLB_CPR_SAFE_END(&cpr, &mmp->mmp_thread_lock);
684 	}
685 
686 	/* Outstanding writes are allowed to complete. */
687 	if (mmp->mmp_zio_root)
688 		zio_wait(mmp->mmp_zio_root);
689 
690 	mmp->mmp_zio_root = NULL;
691 	mmp_thread_exit(mmp, &mmp->mmp_thread, &cpr);
692 }
693 
694 /*
695  * Signal the MMP thread to wake it, when it is sleeping on
696  * its cv.  Used when some module parameter has changed and
697  * we want the thread to know about it.
698  * Only signal if the pool is active and mmp thread is
699  * running, otherwise there is no thread to wake.
700  */
701 static void
mmp_signal_thread(spa_t * spa)702 mmp_signal_thread(spa_t *spa)
703 {
704 	mmp_thread_t *mmp = &spa->spa_mmp;
705 
706 	mutex_enter(&mmp->mmp_thread_lock);
707 	if (mmp->mmp_thread)
708 		cv_broadcast(&mmp->mmp_thread_cv);
709 	mutex_exit(&mmp->mmp_thread_lock);
710 }
711 
712 void
mmp_signal_all_threads(void)713 mmp_signal_all_threads(void)
714 {
715 	spa_t *spa = NULL;
716 
717 	mutex_enter(&spa_namespace_lock);
718 	while ((spa = spa_next(spa))) {
719 		if (spa->spa_state == POOL_STATE_ACTIVE)
720 			mmp_signal_thread(spa);
721 	}
722 	mutex_exit(&spa_namespace_lock);
723 }
724