Root/drivers/md/multipath.c

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
34
35static int multipath_map (struct mpconf *conf)
36{
37    int i, disks = conf->raid_disks;
38
39    /*
40     * Later we do read balancing on the read side
41     * now we use the first available disk.
42     */
43
44    rcu_read_lock();
45    for (i = 0; i < disks; i++) {
46        struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
47        if (rdev && test_bit(In_sync, &rdev->flags)) {
48            atomic_inc(&rdev->nr_pending);
49            rcu_read_unlock();
50            return i;
51        }
52    }
53    rcu_read_unlock();
54
55    printk(KERN_ERR "multipath_map(): no more operational IO paths?\n");
56    return (-1);
57}
58
59static void multipath_reschedule_retry (struct multipath_bh *mp_bh)
60{
61    unsigned long flags;
62    struct mddev *mddev = mp_bh->mddev;
63    struct mpconf *conf = mddev->private;
64
65    spin_lock_irqsave(&conf->device_lock, flags);
66    list_add(&mp_bh->retry_list, &conf->retry_list);
67    spin_unlock_irqrestore(&conf->device_lock, flags);
68    md_wakeup_thread(mddev->thread);
69}
70
71
72/*
73 * multipath_end_bh_io() is called when we have finished servicing a multipathed
74 * operation and are ready to return a success/failure code to the buffer
75 * cache layer.
76 */
77static void multipath_end_bh_io (struct multipath_bh *mp_bh, int err)
78{
79    struct bio *bio = mp_bh->master_bio;
80    struct mpconf *conf = mp_bh->mddev->private;
81
82    bio_endio(bio, err);
83    mempool_free(mp_bh, conf->pool);
84}
85
86static void multipath_end_request(struct bio *bio, int error)
87{
88    int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
89    struct multipath_bh *mp_bh = bio->bi_private;
90    struct mpconf *conf = mp_bh->mddev->private;
91    struct md_rdev *rdev = conf->multipaths[mp_bh->path].rdev;
92
93    if (uptodate)
94        multipath_end_bh_io(mp_bh, 0);
95    else if (!(bio->bi_rw & REQ_RAHEAD)) {
96        /*
97         * oops, IO error:
98         */
99        char b[BDEVNAME_SIZE];
100        md_error (mp_bh->mddev, rdev);
101        printk(KERN_ERR "multipath: %s: rescheduling sector %llu\n",
102               bdevname(rdev->bdev,b),
103               (unsigned long long)bio->bi_sector);
104        multipath_reschedule_retry(mp_bh);
105    } else
106        multipath_end_bh_io(mp_bh, error);
107    rdev_dec_pending(rdev, conf->mddev);
108}
109
110static void multipath_make_request(struct mddev *mddev, struct bio * bio)
111{
112    struct mpconf *conf = mddev->private;
113    struct multipath_bh * mp_bh;
114    struct multipath_info *multipath;
115
116    if (unlikely(bio->bi_rw & REQ_FLUSH)) {
117        md_flush_request(mddev, bio);
118        return;
119    }
120
121    mp_bh = mempool_alloc(conf->pool, GFP_NOIO);
122
123    mp_bh->master_bio = bio;
124    mp_bh->mddev = mddev;
125
126    mp_bh->path = multipath_map(conf);
127    if (mp_bh->path < 0) {
128        bio_endio(bio, -EIO);
129        mempool_free(mp_bh, conf->pool);
130        return;
131    }
132    multipath = conf->multipaths + mp_bh->path;
133
134    mp_bh->bio = *bio;
135    mp_bh->bio.bi_sector += multipath->rdev->data_offset;
136    mp_bh->bio.bi_bdev = multipath->rdev->bdev;
137    mp_bh->bio.bi_rw |= REQ_FAILFAST_TRANSPORT;
138    mp_bh->bio.bi_end_io = multipath_end_request;
139    mp_bh->bio.bi_private = mp_bh;
140    generic_make_request(&mp_bh->bio);
141    return;
142}
143
144static void multipath_status (struct seq_file *seq, struct mddev *mddev)
145{
146    struct mpconf *conf = mddev->private;
147    int i;
148    
149    seq_printf (seq, " [%d/%d] [", conf->raid_disks,
150            conf->raid_disks - mddev->degraded);
151    for (i = 0; i < conf->raid_disks; i++)
152        seq_printf (seq, "%s",
153                   conf->multipaths[i].rdev &&
154                   test_bit(In_sync, &conf->multipaths[i].rdev->flags) ? "U" : "_");
155    seq_printf (seq, "]");
156}
157
158static int multipath_congested(void *data, int bits)
159{
160    struct mddev *mddev = data;
161    struct mpconf *conf = mddev->private;
162    int i, ret = 0;
163
164    if (mddev_congested(mddev, bits))
165        return 1;
166
167    rcu_read_lock();
168    for (i = 0; i < mddev->raid_disks ; i++) {
169        struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
170        if (rdev && !test_bit(Faulty, &rdev->flags)) {
171            struct request_queue *q = bdev_get_queue(rdev->bdev);
172
173            ret |= bdi_congested(&q->backing_dev_info, bits);
174            /* Just like multipath_map, we just check the
175             * first available device
176             */
177            break;
178        }
179    }
180    rcu_read_unlock();
181    return ret;
182}
183
184/*
185 * Careful, this can execute in IRQ contexts as well!
186 */
187static void multipath_error (struct mddev *mddev, struct md_rdev *rdev)
188{
189    struct mpconf *conf = mddev->private;
190    char b[BDEVNAME_SIZE];
191
192    if (conf->raid_disks - mddev->degraded <= 1) {
193        /*
194         * Uh oh, we can do nothing if this is our last path, but
195         * first check if this is a queued request for a device
196         * which has just failed.
197         */
198        printk(KERN_ALERT
199               "multipath: only one IO path left and IO error.\n");
200        /* leave it active... it's all we have */
201        return;
202    }
203    /*
204     * Mark disk as unusable
205     */
206    if (test_and_clear_bit(In_sync, &rdev->flags)) {
207        unsigned long flags;
208        spin_lock_irqsave(&conf->device_lock, flags);
209        mddev->degraded++;
210        spin_unlock_irqrestore(&conf->device_lock, flags);
211    }
212    set_bit(Faulty, &rdev->flags);
213    set_bit(MD_CHANGE_DEVS, &mddev->flags);
214    printk(KERN_ALERT "multipath: IO failure on %s,"
215           " disabling IO path.\n"
216           "multipath: Operation continuing"
217           " on %d IO paths.\n",
218           bdevname(rdev->bdev, b),
219           conf->raid_disks - mddev->degraded);
220}
221
222static void print_multipath_conf (struct mpconf *conf)
223{
224    int i;
225    struct multipath_info *tmp;
226
227    printk("MULTIPATH conf printout:\n");
228    if (!conf) {
229        printk("(conf==NULL)\n");
230        return;
231    }
232    printk(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
233             conf->raid_disks);
234
235    for (i = 0; i < conf->raid_disks; i++) {
236        char b[BDEVNAME_SIZE];
237        tmp = conf->multipaths + i;
238        if (tmp->rdev)
239            printk(" disk%d, o:%d, dev:%s\n",
240                i,!test_bit(Faulty, &tmp->rdev->flags),
241                   bdevname(tmp->rdev->bdev,b));
242    }
243}
244
245
246static int multipath_add_disk(struct mddev *mddev, struct md_rdev *rdev)
247{
248    struct mpconf *conf = mddev->private;
249    struct request_queue *q;
250    int err = -EEXIST;
251    int path;
252    struct multipath_info *p;
253    int first = 0;
254    int last = mddev->raid_disks - 1;
255
256    if (rdev->raid_disk >= 0)
257        first = last = rdev->raid_disk;
258
259    print_multipath_conf(conf);
260
261    for (path = first; path <= last; path++)
262        if ((p=conf->multipaths+path)->rdev == NULL) {
263            q = rdev->bdev->bd_disk->queue;
264            disk_stack_limits(mddev->gendisk, rdev->bdev,
265                      rdev->data_offset << 9);
266
267        /* as we don't honour merge_bvec_fn, we must never risk
268         * violating it, so limit ->max_segments to one, lying
269         * within a single page.
270         * (Note: it is very unlikely that a device with
271         * merge_bvec_fn will be involved in multipath.)
272         */
273            if (q->merge_bvec_fn) {
274                blk_queue_max_segments(mddev->queue, 1);
275                blk_queue_segment_boundary(mddev->queue,
276                               PAGE_CACHE_SIZE - 1);
277            }
278
279            spin_lock_irq(&conf->device_lock);
280            mddev->degraded--;
281            rdev->raid_disk = path;
282            set_bit(In_sync, &rdev->flags);
283            spin_unlock_irq(&conf->device_lock);
284            rcu_assign_pointer(p->rdev, rdev);
285            err = 0;
286            md_integrity_add_rdev(rdev, mddev);
287            break;
288        }
289
290    print_multipath_conf(conf);
291
292    return err;
293}
294
295static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
296{
297    struct mpconf *conf = mddev->private;
298    int err = 0;
299    int number = rdev->raid_disk;
300    struct multipath_info *p = conf->multipaths + number;
301
302    print_multipath_conf(conf);
303
304    if (rdev == p->rdev) {
305        if (test_bit(In_sync, &rdev->flags) ||
306            atomic_read(&rdev->nr_pending)) {
307            printk(KERN_ERR "hot-remove-disk, slot %d is identified"
308                   " but is still operational!\n", number);
309            err = -EBUSY;
310            goto abort;
311        }
312        p->rdev = NULL;
313        synchronize_rcu();
314        if (atomic_read(&rdev->nr_pending)) {
315            /* lost the race, try later */
316            err = -EBUSY;
317            p->rdev = rdev;
318            goto abort;
319        }
320        err = md_integrity_register(mddev);
321    }
322abort:
323
324    print_multipath_conf(conf);
325    return err;
326}
327
328
329
330/*
331 * This is a kernel thread which:
332 *
333 * 1. Retries failed read operations on working multipaths.
334 * 2. Updates the raid superblock when problems encounter.
335 * 3. Performs writes following reads for array syncronising.
336 */
337
338static void multipathd(struct md_thread *thread)
339{
340    struct mddev *mddev = thread->mddev;
341    struct multipath_bh *mp_bh;
342    struct bio *bio;
343    unsigned long flags;
344    struct mpconf *conf = mddev->private;
345    struct list_head *head = &conf->retry_list;
346
347    md_check_recovery(mddev);
348    for (;;) {
349        char b[BDEVNAME_SIZE];
350        spin_lock_irqsave(&conf->device_lock, flags);
351        if (list_empty(head))
352            break;
353        mp_bh = list_entry(head->prev, struct multipath_bh, retry_list);
354        list_del(head->prev);
355        spin_unlock_irqrestore(&conf->device_lock, flags);
356
357        bio = &mp_bh->bio;
358        bio->bi_sector = mp_bh->master_bio->bi_sector;
359        
360        if ((mp_bh->path = multipath_map (conf))<0) {
361            printk(KERN_ALERT "multipath: %s: unrecoverable IO read"
362                " error for block %llu\n",
363                bdevname(bio->bi_bdev,b),
364                (unsigned long long)bio->bi_sector);
365            multipath_end_bh_io(mp_bh, -EIO);
366        } else {
367            printk(KERN_ERR "multipath: %s: redirecting sector %llu"
368                " to another IO path\n",
369                bdevname(bio->bi_bdev,b),
370                (unsigned long long)bio->bi_sector);
371            *bio = *(mp_bh->master_bio);
372            bio->bi_sector += conf->multipaths[mp_bh->path].rdev->data_offset;
373            bio->bi_bdev = conf->multipaths[mp_bh->path].rdev->bdev;
374            bio->bi_rw |= REQ_FAILFAST_TRANSPORT;
375            bio->bi_end_io = multipath_end_request;
376            bio->bi_private = mp_bh;
377            generic_make_request(bio);
378        }
379    }
380    spin_unlock_irqrestore(&conf->device_lock, flags);
381}
382
383static sector_t multipath_size(struct mddev *mddev, sector_t sectors, int raid_disks)
384{
385    WARN_ONCE(sectors || raid_disks,
386          "%s does not support generic reshape\n", __func__);
387
388    return mddev->dev_sectors;
389}
390
391static int multipath_run (struct mddev *mddev)
392{
393    struct mpconf *conf;
394    int disk_idx;
395    struct multipath_info *disk;
396    struct md_rdev *rdev;
397    int working_disks;
398
399    if (md_check_no_bitmap(mddev))
400        return -EINVAL;
401
402    if (mddev->level != LEVEL_MULTIPATH) {
403        printk("multipath: %s: raid level not set to multipath IO (%d)\n",
404               mdname(mddev), mddev->level);
405        goto out;
406    }
407    /*
408     * copy the already verified devices into our private MULTIPATH
409     * bookkeeping area. [whatever we allocate in multipath_run(),
410     * should be freed in multipath_stop()]
411     */
412
413    conf = kzalloc(sizeof(struct mpconf), GFP_KERNEL);
414    mddev->private = conf;
415    if (!conf) {
416        printk(KERN_ERR
417            "multipath: couldn't allocate memory for %s\n",
418            mdname(mddev));
419        goto out;
420    }
421
422    conf->multipaths = kzalloc(sizeof(struct multipath_info)*mddev->raid_disks,
423                   GFP_KERNEL);
424    if (!conf->multipaths) {
425        printk(KERN_ERR
426            "multipath: couldn't allocate memory for %s\n",
427            mdname(mddev));
428        goto out_free_conf;
429    }
430
431    working_disks = 0;
432    rdev_for_each(rdev, mddev) {
433        disk_idx = rdev->raid_disk;
434        if (disk_idx < 0 ||
435            disk_idx >= mddev->raid_disks)
436            continue;
437
438        disk = conf->multipaths + disk_idx;
439        disk->rdev = rdev;
440        disk_stack_limits(mddev->gendisk, rdev->bdev,
441                  rdev->data_offset << 9);
442
443        /* as we don't honour merge_bvec_fn, we must never risk
444         * violating it, not that we ever expect a device with
445         * a merge_bvec_fn to be involved in multipath */
446        if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
447            blk_queue_max_segments(mddev->queue, 1);
448            blk_queue_segment_boundary(mddev->queue,
449                           PAGE_CACHE_SIZE - 1);
450        }
451
452        if (!test_bit(Faulty, &rdev->flags))
453            working_disks++;
454    }
455
456    conf->raid_disks = mddev->raid_disks;
457    conf->mddev = mddev;
458    spin_lock_init(&conf->device_lock);
459    INIT_LIST_HEAD(&conf->retry_list);
460
461    if (!working_disks) {
462        printk(KERN_ERR "multipath: no operational IO paths for %s\n",
463            mdname(mddev));
464        goto out_free_conf;
465    }
466    mddev->degraded = conf->raid_disks - working_disks;
467
468    conf->pool = mempool_create_kmalloc_pool(NR_RESERVED_BUFS,
469                         sizeof(struct multipath_bh));
470    if (conf->pool == NULL) {
471        printk(KERN_ERR
472            "multipath: couldn't allocate memory for %s\n",
473            mdname(mddev));
474        goto out_free_conf;
475    }
476
477    {
478        mddev->thread = md_register_thread(multipathd, mddev,
479                           "multipath");
480        if (!mddev->thread) {
481            printk(KERN_ERR "multipath: couldn't allocate thread"
482                " for %s\n", mdname(mddev));
483            goto out_free_conf;
484        }
485    }
486
487    printk(KERN_INFO
488        "multipath: array %s active with %d out of %d IO paths\n",
489        mdname(mddev), conf->raid_disks - mddev->degraded,
490           mddev->raid_disks);
491    /*
492     * Ok, everything is just fine now
493     */
494    md_set_array_sectors(mddev, multipath_size(mddev, 0, 0));
495
496    mddev->queue->backing_dev_info.congested_fn = multipath_congested;
497    mddev->queue->backing_dev_info.congested_data = mddev;
498
499    if (md_integrity_register(mddev))
500        goto out_free_conf;
501
502    return 0;
503
504out_free_conf:
505    if (conf->pool)
506        mempool_destroy(conf->pool);
507    kfree(conf->multipaths);
508    kfree(conf);
509    mddev->private = NULL;
510out:
511    return -EIO;
512}
513
514
515static int multipath_stop (struct mddev *mddev)
516{
517    struct mpconf *conf = mddev->private;
518
519    md_unregister_thread(&mddev->thread);
520    blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
521    mempool_destroy(conf->pool);
522    kfree(conf->multipaths);
523    kfree(conf);
524    mddev->private = NULL;
525    return 0;
526}
527
528static struct md_personality multipath_personality =
529{
530    .name = "multipath",
531    .level = LEVEL_MULTIPATH,
532    .owner = THIS_MODULE,
533    .make_request = multipath_make_request,
534    .run = multipath_run,
535    .stop = multipath_stop,
536    .status = multipath_status,
537    .error_handler = multipath_error,
538    .hot_add_disk = multipath_add_disk,
539    .hot_remove_disk= multipath_remove_disk,
540    .size = multipath_size,
541};
542
543static int __init multipath_init (void)
544{
545    return register_md_personality (&multipath_personality);
546}
547
548static void __exit multipath_exit (void)
549{
550    unregister_md_personality (&multipath_personality);
551}
552
553module_init(multipath_init);
554module_exit(multipath_exit);
555MODULE_LICENSE("GPL");
556MODULE_DESCRIPTION("simple multi-path personality for MD");
557MODULE_ALIAS("md-personality-7"); /* MULTIPATH */
558MODULE_ALIAS("md-multipath");
559MODULE_ALIAS("md-level--4");
560

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