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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: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Jonathan Brassow 2008-02-08 02:11:29 +00:00 committed by Alasdair G Kergon
parent d74f81f8ad
commit 72f4b31410
1 changed files with 224 additions and 26 deletions
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250
drivers/md/dm-raid1.c
View File

@ -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) {
for (i = 0; i < ms->nr_mirrors; i++)
if (test_bit(i, &error))
fail_mirror(ms->mirror + i, DM_RAID1_WRITE_ERROR);
else
uptodate = 1;
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)) {
/*
* only error the io if all mirrors failed.
* FIXME: bogus
* Need to raise event. Since raising
* events can block, we need to do it in
* the main thread.
*/
uptodate = 0;
for (i = 0; i < ms->nr_mirrors; i++)
if (!test_bit(i, &error)) {
uptodate = 1;
break;
}
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);