Commit 72f4b314 authored by Jonathan Brassow's avatar Jonathan Brassow Committed by Alasdair G Kergon
Browse files

dm raid1: handle write failures 



This patch gives mirror the ability to handle device failures
during normal write operations.

The 'write_callback' function is called when a write completes.
If all the writes failed or succeeded, we report failure or
success respectively.  If some of the writes failed, we call
fail_mirror; which increments the error count for the device, notes
the type of error encountered (DM_RAID1_WRITE_ERROR),  and
selects a new primary (if necessary).  Note that the primary
device can never change while the mirror is not in-sync (IOW,
while recovery is happening.)  This means that the scenario
where a failed write changes the primary and gives
recovery_complete a chance to misread the primary never happens.
The fact that the primary can change has necessitated the change
to the default_mirror field.  We need to protect against reading
garbage while the primary changes.  We then add the bio to a new
list in the mirror set, 'failures'.  For every bio in the 'failures'
list, we call a new function, '__bio_mark_nosync', where we mark
the region 'not-in-sync' in the log and properly set the region
state as, RH_NOSYNC.  Userspace must also be notified of the
failure.  This is done by 'raising an event' (dm_table_event()).
If fail_mirror is called in process context the event can be raised
right away.  If in interrupt context, the event is deferred to the
kmirrord thread - which raises the event if 'event_waiting' is set.

Backwards compatibility is maintained by ignoring errors if
the DM_FEATURES_HANDLE_ERRORS flag is not present.

Signed-off-by: default avatarJonathan Brassow <jbrassow@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent d74f81f8

drivers/md/dm-raid1.c

+224 −26
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
#include <linux/vmalloc.h>

#include <linux/workqueue.h>

#include <linux/log2.h>

#include <linux/hardirq.h>



#define DM_MSG_PREFIX "raid1"

#define DM_IO_PAGES 64
@@ -113,9 +114,16 @@ struct region { 
/*-----------------------------------------------------------------

 * Mirror set structures.

 *---------------------------------------------------------------*/

enum dm_raid1_error {

	DM_RAID1_WRITE_ERROR,

	DM_RAID1_SYNC_ERROR,

	DM_RAID1_READ_ERROR

};



struct mirror {

	struct mirror_set *ms;

	atomic_t error_count;

	uint32_t error_type;

	struct dm_dev *dev;

	sector_t offset;

};
@@ -127,9 +135,10 @@ struct mirror_set { 
	struct kcopyd_client *kcopyd_client;

	uint64_t features;



	spinlock_t lock;	/* protects the next two lists */

	spinlock_t lock;	/* protects the lists */

	struct bio_list reads;

	struct bio_list writes;

	struct bio_list failures;



	struct dm_io_client *io_client;
@@ -138,10 +147,11 @@ struct mirror_set { 
	int in_sync;

	int log_failure;



	struct mirror *default_mirror;	/* Default mirror */

	atomic_t default_mirror;	/* Default mirror */



	struct workqueue_struct *kmirrord_wq;

	struct work_struct kmirrord_work;

	struct work_struct trigger_event;



	unsigned int nr_mirrors;

	struct mirror mirror[0];
@@ -646,6 +656,77 @@ static void bio_set_ms(struct bio *bio, struct mirror_set *ms) 
	bio->bi_next = (struct bio *) ms;

}



static struct mirror *get_default_mirror(struct mirror_set *ms)

{

	return &ms->mirror[atomic_read(&ms->default_mirror)];

}



static void set_default_mirror(struct mirror *m)

{

	struct mirror_set *ms = m->ms;

	struct mirror *m0 = &(ms->mirror[0]);



	atomic_set(&ms->default_mirror, m - m0);

}



/* fail_mirror

 * @m: mirror device to fail

 * @error_type: one of the enum's, DM_RAID1_*_ERROR

 *

 * If errors are being handled, record the type of

 * error encountered for this device.  If this type

 * of error has already been recorded, we can return;

 * otherwise, we must signal userspace by triggering

 * an event.  Additionally, if the device is the

 * primary device, we must choose a new primary, but

 * only if the mirror is in-sync.

 *

 * This function must not block.

 */

static void fail_mirror(struct mirror *m, enum dm_raid1_error error_type)

{

	struct mirror_set *ms = m->ms;

	struct mirror *new;



	if (!errors_handled(ms))

		return;



	/*

	 * error_count is used for nothing more than a

	 * simple way to tell if a device has encountered

	 * errors.

	 */

	atomic_inc(&m->error_count);



	if (test_and_set_bit(error_type, &m->error_type))

		return;



	if (m != get_default_mirror(ms))

		goto out;



	if (!ms->in_sync) {

		/*

		 * Better to issue requests to same failing device

		 * than to risk returning corrupt data.

		 */

		DMERR("Primary mirror (%s) failed while out-of-sync: "

		      "Reads may fail.", m->dev->name);

		goto out;

	}



	for (new = ms->mirror; new < ms->mirror + ms->nr_mirrors; new++)

		if (!atomic_read(&new->error_count)) {

			set_default_mirror(new);

			break;

		}



	if (unlikely(new == ms->mirror + ms->nr_mirrors))

		DMWARN("All sides of mirror have failed.");



out:

	schedule_work(&ms->trigger_event);

}



/*-----------------------------------------------------------------

 * Recovery.

 *
@@ -678,7 +759,7 @@ static int recover(struct mirror_set *ms, struct region *reg) 
	unsigned long flags = 0;



	/* fill in the source */

	m = ms->default_mirror;

	m = get_default_mirror(ms);

	from.bdev = m->dev->bdev;

	from.sector = m->offset + region_to_sector(reg->rh, reg->key);

	if (reg->key == (ms->nr_regions - 1)) {
@@ -694,7 +775,7 @@ static int recover(struct mirror_set *ms, struct region *reg) 


	/* fill in the destinations */

	for (i = 0, dest = to; i < ms->nr_mirrors; i++) {

		if (&ms->mirror[i] == ms->default_mirror)

		if (&ms->mirror[i] == get_default_mirror(ms))

			continue;



		m = ms->mirror + i;
@@ -749,7 +830,7 @@ static void do_recovery(struct mirror_set *ms) 
static struct mirror *choose_mirror(struct mirror_set *ms, sector_t sector)

{

	/* FIXME: add read balancing */

	return ms->default_mirror;

	return get_default_mirror(ms);

}



/*
@@ -776,7 +857,7 @@ static void do_reads(struct mirror_set *ms, struct bio_list *reads) 
		if (rh_in_sync(&ms->rh, region, 1))

			m = choose_mirror(ms, bio->bi_sector);

		else

			m = ms->default_mirror;

			m = get_default_mirror(ms);



		map_bio(ms, m, bio);

		generic_make_request(bio);
@@ -793,12 +874,67 @@ static void do_reads(struct mirror_set *ms, struct bio_list *reads) 
 * RECOVERING:	delay the io until recovery completes

 * NOSYNC:	increment pending, just write to the default mirror

 *---------------------------------------------------------------*/



/* __bio_mark_nosync

 * @ms

 * @bio

 * @done

 * @error

 *

 * The bio was written on some mirror(s) but failed on other mirror(s).

 * We can successfully endio the bio but should avoid the region being

 * marked clean by setting the state RH_NOSYNC.

 *

 * This function is _not_ safe in interrupt context!

 */

static void __bio_mark_nosync(struct mirror_set *ms,

			      struct bio *bio, unsigned done, int error)

{

	unsigned long flags;

	struct region_hash *rh = &ms->rh;

	struct dirty_log *log = ms->rh.log;

	struct region *reg;

	region_t region = bio_to_region(rh, bio);

	int recovering = 0;



	/* We must inform the log that the sync count has changed. */

	log->type->set_region_sync(log, region, 0);

	ms->in_sync = 0;



	read_lock(&rh->hash_lock);

	reg = __rh_find(rh, region);

	read_unlock(&rh->hash_lock);



	/* region hash entry should exist because write was in-flight */

	BUG_ON(!reg);

	BUG_ON(!list_empty(&reg->list));



	spin_lock_irqsave(&rh->region_lock, flags);

	/*

	 * Possible cases:

	 *   1) RH_DIRTY

	 *   2) RH_NOSYNC: was dirty, other preceeding writes failed

	 *   3) RH_RECOVERING: flushing pending writes

	 * Either case, the region should have not been connected to list.

	 */

	recovering = (reg->state == RH_RECOVERING);

	reg->state = RH_NOSYNC;

	BUG_ON(!list_empty(&reg->list));

	spin_unlock_irqrestore(&rh->region_lock, flags);



	bio_endio(bio, error);

	if (recovering)

		complete_resync_work(reg, 0);

}



static void write_callback(unsigned long error, void *context)

{

	unsigned int i;

	int uptodate = 1;

	unsigned i, ret = 0;

	struct bio *bio = (struct bio *) context;

	struct mirror_set *ms;

	int uptodate = 0;

	int should_wake = 0;

	unsigned long flags;



	ms = bio_get_ms(bio);

	bio_set_ms(bio, NULL);
@@ -809,20 +945,36 @@ static void write_callback(unsigned long error, void *context) 
	 * This way we handle both writes to SYNC and NOSYNC

	 * regions with the same code.

	 */

	if (likely(!error))

		goto out;



	if (error) {

		/*

		 * only error the io if all mirrors failed.

		 * FIXME: bogus

		 */

		uptodate = 0;

	for (i = 0; i < ms->nr_mirrors; i++)

			if (!test_bit(i, &error)) {

		if (test_bit(i, &error))

			fail_mirror(ms->mirror + i, DM_RAID1_WRITE_ERROR);

		else

			uptodate = 1;

				break;

			}



	if (unlikely(!uptodate)) {

		DMERR("All replicated volumes dead, failing I/O");

		/* None of the writes succeeded, fail the I/O. */

		ret = -EIO;

	} else if (errors_handled(ms)) {

		/*

		 * Need to raise event.  Since raising

		 * events can block, we need to do it in

		 * the main thread.

		 */

		spin_lock_irqsave(&ms->lock, flags);

		if (!ms->failures.head)

			should_wake = 1;

		bio_list_add(&ms->failures, bio);

		spin_unlock_irqrestore(&ms->lock, flags);

		if (should_wake)

			wake(ms);

		return;

	}

	bio_endio(bio, 0);

out:

	bio_endio(bio, ret);

}



static void do_write(struct mirror_set *ms, struct bio *bio)
@@ -910,33 +1062,75 @@ static void do_writes(struct mirror_set *ms, struct bio_list *writes) 
		rh_delay(&ms->rh, bio);



	while ((bio = bio_list_pop(&nosync))) {

		map_bio(ms, ms->default_mirror, bio);

		map_bio(ms, get_default_mirror(ms), bio);

		generic_make_request(bio);

	}

}



static void do_failures(struct mirror_set *ms, struct bio_list *failures)

{

	struct bio *bio;



	if (!failures->head)

		return;



	while ((bio = bio_list_pop(failures)))

		__bio_mark_nosync(ms, bio, bio->bi_size, 0);

}



static void trigger_event(struct work_struct *work)

{

	struct mirror_set *ms =

		container_of(work, struct mirror_set, trigger_event);



	dm_table_event(ms->ti->table);

}



/*-----------------------------------------------------------------

 * kmirrord

 *---------------------------------------------------------------*/

static void do_mirror(struct work_struct *work)

static int _do_mirror(struct work_struct *work)

{

	struct mirror_set *ms =container_of(work, struct mirror_set,

					    kmirrord_work);

	struct bio_list reads, writes;

	struct bio_list reads, writes, failures;

	unsigned long flags;



	spin_lock(&ms->lock);

	spin_lock_irqsave(&ms->lock, flags);

	reads = ms->reads;

	writes = ms->writes;

	failures = ms->failures;

	bio_list_init(&ms->reads);

	bio_list_init(&ms->writes);

	spin_unlock(&ms->lock);

	bio_list_init(&ms->failures);

	spin_unlock_irqrestore(&ms->lock, flags);



	rh_update_states(&ms->rh);

	do_recovery(ms);

	do_reads(ms, &reads);

	do_writes(ms, &writes);

	do_failures(ms, &failures);



	return (ms->failures.head) ? 1 : 0;

}



static void do_mirror(struct work_struct *work)

{

	/*

	 * If _do_mirror returns 1, we give it

	 * another shot.  This helps for cases like

	 * 'suspend' where we call flush_workqueue

	 * and expect all work to be finished.  If

	 * a failure happens during a suspend, we

	 * couldn't issue a 'wake' because it would

	 * not be honored.  Therefore, we return '1'

	 * from _do_mirror, and retry here.

	 */

	while (_do_mirror(work))

		schedule();

}





/*-----------------------------------------------------------------

 * Target functions

 *---------------------------------------------------------------*/
@@ -965,7 +1159,7 @@ static struct mirror_set *alloc_context(unsigned int nr_mirrors, 
	ms->nr_mirrors = nr_mirrors;

	ms->nr_regions = dm_sector_div_up(ti->len, region_size);

	ms->in_sync = 0;

	ms->default_mirror = &ms->mirror[DEFAULT_MIRROR];

	atomic_set(&ms->default_mirror, DEFAULT_MIRROR);



	ms->io_client = dm_io_client_create(DM_IO_PAGES);

	if (IS_ERR(ms->io_client)) {
@@ -1019,6 +1213,8 @@ static int get_mirror(struct mirror_set *ms, struct dm_target *ti, 
	}



	ms->mirror[mirror].ms = ms;

	atomic_set(&(ms->mirror[mirror].error_count), 0);

	ms->mirror[mirror].error_type = 0;

	ms->mirror[mirror].offset = offset;



	return 0;
@@ -1171,6 +1367,7 @@ static int mirror_ctr(struct dm_target *ti, unsigned int argc, char **argv) 
		goto err_free_context;

	}

	INIT_WORK(&ms->kmirrord_work, do_mirror);

	INIT_WORK(&ms->trigger_event, trigger_event);



	r = parse_features(ms, argc, argv, &args_used);

	if (r)
@@ -1220,14 +1417,15 @@ static void mirror_dtr(struct dm_target *ti) 


static void queue_bio(struct mirror_set *ms, struct bio *bio, int rw)

{

	unsigned long flags;

	int should_wake = 0;

	struct bio_list *bl;



	bl = (rw == WRITE) ? &ms->writes : &ms->reads;

	spin_lock(&ms->lock);

	spin_lock_irqsave(&ms->lock, flags);

	should_wake = !(bl->head);

	bio_list_add(bl, bio);

	spin_unlock(&ms->lock);

	spin_unlock_irqrestore(&ms->lock, flags);



	if (should_wake)

		wake(ms);

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