linux/drivers/md/multipath.c
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   1/*
   2 * multipath.c : Multiple Devices driver for Linux
   3 *
   4 * Copyright (C) 1999, 2000, 2001 Ingo Molnar, Red Hat
   5 *
   6 * Copyright (C) 1996, 1997, 1998 Ingo Molnar, Miguel de Icaza, Gadi Oxman
   7 *
   8 * MULTIPATH management functions.
   9 *
  10 * derived from raid1.c.
  11 *
  12 * This program is free software; you can redistribute it and/or modify
  13 * it under the terms of the GNU General Public License as published by
  14 * the Free Software Foundation; either version 2, or (at your option)
  15 * any later version.
  16 *
  17 * You should have received a copy of the GNU General Public License
  18 * (for example /usr/src/linux/COPYING); if not, write to the Free
  19 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20 */
  21
  22#include <linux/blkdev.h>
  23#include <linux/module.h>
  24#include <linux/raid/md_u.h>
  25#include <linux/seq_file.h>
  26#include <linux/slab.h>
  27#include "md.h"
  28#include "multipath.h"
  29
  30#define MAX_WORK_PER_DISK 128
  31
  32#define NR_RESERVED_BUFS        32
  33
  34static int multipath_map (struct mpconf *conf)
  35{
  36        int i, disks = conf->raid_disks;
  37
  38        /*
  39         * Later we do read balancing on the read side
  40         * now we use the first available disk.
  41         */
  42
  43        rcu_read_lock();
  44        for (i = 0; i < disks; i++) {
  45                struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
  46                if (rdev && test_bit(In_sync, &rdev->flags)) {
  47                        atomic_inc(&rdev->nr_pending);
  48                        rcu_read_unlock();
  49                        return i;
  50                }
  51        }
  52        rcu_read_unlock();
  53
  54        printk(KERN_ERR "multipath_map(): no more operational IO paths?\n");
  55        return (-1);
  56}
  57
  58static void multipath_reschedule_retry (struct multipath_bh *mp_bh)
  59{
  60        unsigned long flags;
  61        struct mddev *mddev = mp_bh->mddev;
  62        struct mpconf *conf = mddev->private;
  63
  64        spin_lock_irqsave(&conf->device_lock, flags);
  65        list_add(&mp_bh->retry_list, &conf->retry_list);
  66        spin_unlock_irqrestore(&conf->device_lock, flags);
  67        md_wakeup_thread(mddev->thread);
  68}
  69
  70/*
  71 * multipath_end_bh_io() is called when we have finished servicing a multipathed
  72 * operation and are ready to return a success/failure code to the buffer
  73 * cache layer.
  74 */
  75static void multipath_end_bh_io (struct multipath_bh *mp_bh, int err)
  76{
  77        struct bio *bio = mp_bh->master_bio;
  78        struct mpconf *conf = mp_bh->mddev->private;
  79
  80        bio_endio(bio, err);
  81        mempool_free(mp_bh, conf->pool);
  82}
  83
  84static void multipath_end_request(struct bio *bio, int error)
  85{
  86        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  87        struct multipath_bh *mp_bh = bio->bi_private;
  88        struct mpconf *conf = mp_bh->mddev->private;
  89        struct md_rdev *rdev = conf->multipaths[mp_bh->path].rdev;
  90
  91        if (uptodate)
  92                multipath_end_bh_io(mp_bh, 0);
  93        else if (!(bio->bi_rw & REQ_RAHEAD)) {
  94                /*
  95                 * oops, IO error:
  96                 */
  97                char b[BDEVNAME_SIZE];
  98                md_error (mp_bh->mddev, rdev);
  99                printk(KERN_ERR "multipath: %s: rescheduling sector %llu\n",
 100                       bdevname(rdev->bdev,b),
 101                       (unsigned long long)bio->bi_iter.bi_sector);
 102                multipath_reschedule_retry(mp_bh);
 103        } else
 104                multipath_end_bh_io(mp_bh, error);
 105        rdev_dec_pending(rdev, conf->mddev);
 106}
 107
 108static void multipath_make_request(struct mddev *mddev, struct bio * bio)
 109{
 110        struct mpconf *conf = mddev->private;
 111        struct multipath_bh * mp_bh;
 112        struct multipath_info *multipath;
 113
 114        if (unlikely(bio->bi_rw & REQ_FLUSH)) {
 115                md_flush_request(mddev, bio);
 116                return;
 117        }
 118
 119        mp_bh = mempool_alloc(conf->pool, GFP_NOIO);
 120
 121        mp_bh->master_bio = bio;
 122        mp_bh->mddev = mddev;
 123
 124        mp_bh->path = multipath_map(conf);
 125        if (mp_bh->path < 0) {
 126                bio_endio(bio, -EIO);
 127                mempool_free(mp_bh, conf->pool);
 128                return;
 129        }
 130        multipath = conf->multipaths + mp_bh->path;
 131
 132        mp_bh->bio = *bio;
 133        mp_bh->bio.bi_iter.bi_sector += multipath->rdev->data_offset;
 134        mp_bh->bio.bi_bdev = multipath->rdev->bdev;
 135        mp_bh->bio.bi_rw |= REQ_FAILFAST_TRANSPORT;
 136        mp_bh->bio.bi_end_io = multipath_end_request;
 137        mp_bh->bio.bi_private = mp_bh;
 138        generic_make_request(&mp_bh->bio);
 139        return;
 140}
 141
 142static void multipath_status (struct seq_file *seq, struct mddev *mddev)
 143{
 144        struct mpconf *conf = mddev->private;
 145        int i;
 146
 147        seq_printf (seq, " [%d/%d] [", conf->raid_disks,
 148                    conf->raid_disks - mddev->degraded);
 149        for (i = 0; i < conf->raid_disks; i++)
 150                seq_printf (seq, "%s",
 151                               conf->multipaths[i].rdev &&
 152                               test_bit(In_sync, &conf->multipaths[i].rdev->flags) ? "U" : "_");
 153        seq_printf (seq, "]");
 154}
 155
 156static int multipath_congested(void *data, int bits)
 157{
 158        struct mddev *mddev = data;
 159        struct mpconf *conf = mddev->private;
 160        int i, ret = 0;
 161
 162        if (mddev_congested(mddev, bits))
 163                return 1;
 164
 165        rcu_read_lock();
 166        for (i = 0; i < mddev->raid_disks ; i++) {
 167                struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
 168                if (rdev && !test_bit(Faulty, &rdev->flags)) {
 169                        struct request_queue *q = bdev_get_queue(rdev->bdev);
 170
 171                        ret |= bdi_congested(&q->backing_dev_info, bits);
 172                        /* Just like multipath_map, we just check the
 173                         * first available device
 174                         */
 175                        break;
 176                }
 177        }
 178        rcu_read_unlock();
 179        return ret;
 180}
 181
 182/*
 183 * Careful, this can execute in IRQ contexts as well!
 184 */
 185static void multipath_error (struct mddev *mddev, struct md_rdev *rdev)
 186{
 187        struct mpconf *conf = mddev->private;
 188        char b[BDEVNAME_SIZE];
 189
 190        if (conf->raid_disks - mddev->degraded <= 1) {
 191                /*
 192                 * Uh oh, we can do nothing if this is our last path, but
 193                 * first check if this is a queued request for a device
 194                 * which has just failed.
 195                 */
 196                printk(KERN_ALERT
 197                       "multipath: only one IO path left and IO error.\n");
 198                /* leave it active... it's all we have */
 199                return;
 200        }
 201        /*
 202         * Mark disk as unusable
 203         */
 204        if (test_and_clear_bit(In_sync, &rdev->flags)) {
 205                unsigned long flags;
 206                spin_lock_irqsave(&conf->device_lock, flags);
 207                mddev->degraded++;
 208                spin_unlock_irqrestore(&conf->device_lock, flags);
 209        }
 210        set_bit(Faulty, &rdev->flags);
 211        set_bit(MD_CHANGE_DEVS, &mddev->flags);
 212        printk(KERN_ALERT "multipath: IO failure on %s,"
 213               " disabling IO path.\n"
 214               "multipath: Operation continuing"
 215               " on %d IO paths.\n",
 216               bdevname(rdev->bdev, b),
 217               conf->raid_disks - mddev->degraded);
 218}
 219
 220static void print_multipath_conf (struct mpconf *conf)
 221{
 222        int i;
 223        struct multipath_info *tmp;
 224
 225        printk("MULTIPATH conf printout:\n");
 226        if (!conf) {
 227                printk("(conf==NULL)\n");
 228                return;
 229        }
 230        printk(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
 231                         conf->raid_disks);
 232
 233        for (i = 0; i < conf->raid_disks; i++) {
 234                char b[BDEVNAME_SIZE];
 235                tmp = conf->multipaths + i;
 236                if (tmp->rdev)
 237                        printk(" disk%d, o:%d, dev:%s\n",
 238                                i,!test_bit(Faulty, &tmp->rdev->flags),
 239                               bdevname(tmp->rdev->bdev,b));
 240        }
 241}
 242
 243static int multipath_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 244{
 245        struct mpconf *conf = mddev->private;
 246        struct request_queue *q;
 247        int err = -EEXIST;
 248        int path;
 249        struct multipath_info *p;
 250        int first = 0;
 251        int last = mddev->raid_disks - 1;
 252
 253        if (rdev->raid_disk >= 0)
 254                first = last = rdev->raid_disk;
 255
 256        print_multipath_conf(conf);
 257
 258        for (path = first; path <= last; path++)
 259                if ((p=conf->multipaths+path)->rdev == NULL) {
 260                        q = rdev->bdev->bd_disk->queue;
 261                        disk_stack_limits(mddev->gendisk, rdev->bdev,
 262                                          rdev->data_offset << 9);
 263
 264                /* as we don't honour merge_bvec_fn, we must never risk
 265                 * violating it, so limit ->max_segments to one, lying
 266                 * within a single page.
 267                 * (Note: it is very unlikely that a device with
 268                 * merge_bvec_fn will be involved in multipath.)
 269                 */
 270                        if (q->merge_bvec_fn) {
 271                                blk_queue_max_segments(mddev->queue, 1);
 272                                blk_queue_segment_boundary(mddev->queue,
 273                                                           PAGE_CACHE_SIZE - 1);
 274                        }
 275
 276                        spin_lock_irq(&conf->device_lock);
 277                        mddev->degraded--;
 278                        rdev->raid_disk = path;
 279                        set_bit(In_sync, &rdev->flags);
 280                        spin_unlock_irq(&conf->device_lock);
 281                        rcu_assign_pointer(p->rdev, rdev);
 282                        err = 0;
 283                        md_integrity_add_rdev(rdev, mddev);
 284                        break;
 285                }
 286
 287        print_multipath_conf(conf);
 288
 289        return err;
 290}
 291
 292static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 293{
 294        struct mpconf *conf = mddev->private;
 295        int err = 0;
 296        int number = rdev->raid_disk;
 297        struct multipath_info *p = conf->multipaths + number;
 298
 299        print_multipath_conf(conf);
 300
 301        if (rdev == p->rdev) {
 302                if (test_bit(In_sync, &rdev->flags) ||
 303                    atomic_read(&rdev->nr_pending)) {
 304                        printk(KERN_ERR "hot-remove-disk, slot %d is identified"
 305                               " but is still operational!\n", number);
 306                        err = -EBUSY;
 307                        goto abort;
 308                }
 309                p->rdev = NULL;
 310                synchronize_rcu();
 311                if (atomic_read(&rdev->nr_pending)) {
 312                        /* lost the race, try later */
 313                        err = -EBUSY;
 314                        p->rdev = rdev;
 315                        goto abort;
 316                }
 317                err = md_integrity_register(mddev);
 318        }
 319abort:
 320
 321        print_multipath_conf(conf);
 322        return err;
 323}
 324
 325/*
 326 * This is a kernel thread which:
 327 *
 328 *      1.      Retries failed read operations on working multipaths.
 329 *      2.      Updates the raid superblock when problems encounter.
 330 *      3.      Performs writes following reads for array syncronising.
 331 */
 332
 333static void multipathd(struct md_thread *thread)
 334{
 335        struct mddev *mddev = thread->mddev;
 336        struct multipath_bh *mp_bh;
 337        struct bio *bio;
 338        unsigned long flags;
 339        struct mpconf *conf = mddev->private;
 340        struct list_head *head = &conf->retry_list;
 341
 342        md_check_recovery(mddev);
 343        for (;;) {
 344                char b[BDEVNAME_SIZE];
 345                spin_lock_irqsave(&conf->device_lock, flags);
 346                if (list_empty(head))
 347                        break;
 348                mp_bh = list_entry(head->prev, struct multipath_bh, retry_list);
 349                list_del(head->prev);
 350                spin_unlock_irqrestore(&conf->device_lock, flags);
 351
 352                bio = &mp_bh->bio;
 353                bio->bi_iter.bi_sector = mp_bh->master_bio->bi_iter.bi_sector;
 354
 355                if ((mp_bh->path = multipath_map (conf))<0) {
 356                        printk(KERN_ALERT "multipath: %s: unrecoverable IO read"
 357                                " error for block %llu\n",
 358                                bdevname(bio->bi_bdev,b),
 359                                (unsigned long long)bio->bi_iter.bi_sector);
 360                        multipath_end_bh_io(mp_bh, -EIO);
 361                } else {
 362                        printk(KERN_ERR "multipath: %s: redirecting sector %llu"
 363                                " to another IO path\n",
 364                                bdevname(bio->bi_bdev,b),
 365                                (unsigned long long)bio->bi_iter.bi_sector);
 366                        *bio = *(mp_bh->master_bio);
 367                        bio->bi_iter.bi_sector +=
 368                                conf->multipaths[mp_bh->path].rdev->data_offset;
 369                        bio->bi_bdev = conf->multipaths[mp_bh->path].rdev->bdev;
 370                        bio->bi_rw |= REQ_FAILFAST_TRANSPORT;
 371                        bio->bi_end_io = multipath_end_request;
 372                        bio->bi_private = mp_bh;
 373                        generic_make_request(bio);
 374                }
 375        }
 376        spin_unlock_irqrestore(&conf->device_lock, flags);
 377}
 378
 379static sector_t multipath_size(struct mddev *mddev, sector_t sectors, int raid_disks)
 380{
 381        WARN_ONCE(sectors || raid_disks,
 382                  "%s does not support generic reshape\n", __func__);
 383
 384        return mddev->dev_sectors;
 385}
 386
 387static int multipath_run (struct mddev *mddev)
 388{
 389        struct mpconf *conf;
 390        int disk_idx;
 391        struct multipath_info *disk;
 392        struct md_rdev *rdev;
 393        int working_disks;
 394
 395        if (md_check_no_bitmap(mddev))
 396                return -EINVAL;
 397
 398        if (mddev->level != LEVEL_MULTIPATH) {
 399                printk("multipath: %s: raid level not set to multipath IO (%d)\n",
 400                       mdname(mddev), mddev->level);
 401                goto out;
 402        }
 403        /*
 404         * copy the already verified devices into our private MULTIPATH
 405         * bookkeeping area. [whatever we allocate in multipath_run(),
 406         * should be freed in multipath_stop()]
 407         */
 408
 409        conf = kzalloc(sizeof(struct mpconf), GFP_KERNEL);
 410        mddev->private = conf;
 411        if (!conf) {
 412                printk(KERN_ERR
 413                        "multipath: couldn't allocate memory for %s\n",
 414                        mdname(mddev));
 415                goto out;
 416        }
 417
 418        conf->multipaths = kzalloc(sizeof(struct multipath_info)*mddev->raid_disks,
 419                                   GFP_KERNEL);
 420        if (!conf->multipaths) {
 421                printk(KERN_ERR
 422                        "multipath: couldn't allocate memory for %s\n",
 423                        mdname(mddev));
 424                goto out_free_conf;
 425        }
 426
 427        working_disks = 0;
 428        rdev_for_each(rdev, mddev) {
 429                disk_idx = rdev->raid_disk;
 430                if (disk_idx < 0 ||
 431                    disk_idx >= mddev->raid_disks)
 432                        continue;
 433
 434                disk = conf->multipaths + disk_idx;
 435                disk->rdev = rdev;
 436                disk_stack_limits(mddev->gendisk, rdev->bdev,
 437                                  rdev->data_offset << 9);
 438
 439                /* as we don't honour merge_bvec_fn, we must never risk
 440                 * violating it, not that we ever expect a device with
 441                 * a merge_bvec_fn to be involved in multipath */
 442                if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
 443                        blk_queue_max_segments(mddev->queue, 1);
 444                        blk_queue_segment_boundary(mddev->queue,
 445                                                   PAGE_CACHE_SIZE - 1);
 446                }
 447
 448                if (!test_bit(Faulty, &rdev->flags))
 449                        working_disks++;
 450        }
 451
 452        conf->raid_disks = mddev->raid_disks;
 453        conf->mddev = mddev;
 454        spin_lock_init(&conf->device_lock);
 455        INIT_LIST_HEAD(&conf->retry_list);
 456
 457        if (!working_disks) {
 458                printk(KERN_ERR "multipath: no operational IO paths for %s\n",
 459                        mdname(mddev));
 460                goto out_free_conf;
 461        }
 462        mddev->degraded = conf->raid_disks - working_disks;
 463
 464        conf->pool = mempool_create_kmalloc_pool(NR_RESERVED_BUFS,
 465                                                 sizeof(struct multipath_bh));
 466        if (conf->pool == NULL) {
 467                printk(KERN_ERR
 468                        "multipath: couldn't allocate memory for %s\n",
 469                        mdname(mddev));
 470                goto out_free_conf;
 471        }
 472
 473        {
 474                mddev->thread = md_register_thread(multipathd, mddev,
 475                                                   "multipath");
 476                if (!mddev->thread) {
 477                        printk(KERN_ERR "multipath: couldn't allocate thread"
 478                                " for %s\n", mdname(mddev));
 479                        goto out_free_conf;
 480                }
 481        }
 482
 483        printk(KERN_INFO
 484                "multipath: array %s active with %d out of %d IO paths\n",
 485                mdname(mddev), conf->raid_disks - mddev->degraded,
 486               mddev->raid_disks);
 487        /*
 488         * Ok, everything is just fine now
 489         */
 490        md_set_array_sectors(mddev, multipath_size(mddev, 0, 0));
 491
 492        mddev->queue->backing_dev_info.congested_fn = multipath_congested;
 493        mddev->queue->backing_dev_info.congested_data = mddev;
 494
 495        if (md_integrity_register(mddev))
 496                goto out_free_conf;
 497
 498        return 0;
 499
 500out_free_conf:
 501        if (conf->pool)
 502                mempool_destroy(conf->pool);
 503        kfree(conf->multipaths);
 504        kfree(conf);
 505        mddev->private = NULL;
 506out:
 507        return -EIO;
 508}
 509
 510static int multipath_stop (struct mddev *mddev)
 511{
 512        struct mpconf *conf = mddev->private;
 513
 514        md_unregister_thread(&mddev->thread);
 515        blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
 516        mempool_destroy(conf->pool);
 517        kfree(conf->multipaths);
 518        kfree(conf);
 519        mddev->private = NULL;
 520        return 0;
 521}
 522
 523static struct md_personality multipath_personality =
 524{
 525        .name           = "multipath",
 526        .level          = LEVEL_MULTIPATH,
 527        .owner          = THIS_MODULE,
 528        .make_request   = multipath_make_request,
 529        .run            = multipath_run,
 530        .stop           = multipath_stop,
 531        .status         = multipath_status,
 532        .error_handler  = multipath_error,
 533        .hot_add_disk   = multipath_add_disk,
 534        .hot_remove_disk= multipath_remove_disk,
 535        .size           = multipath_size,
 536};
 537
 538static int __init multipath_init (void)
 539{
 540        return register_md_personality (&multipath_personality);
 541}
 542
 543static void __exit multipath_exit (void)
 544{
 545        unregister_md_personality (&multipath_personality);
 546}
 547
 548module_init(multipath_init);
 549module_exit(multipath_exit);
 550MODULE_LICENSE("GPL");
 551MODULE_DESCRIPTION("simple multi-path personality for MD");
 552MODULE_ALIAS("md-personality-7"); /* MULTIPATH */
 553MODULE_ALIAS("md-multipath");
 554MODULE_ALIAS("md-level--4");
 555