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>
diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 31123d4a..4e1e04d 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -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 @@
/*-----------------------------------------------------------------
* 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 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 @@
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 @@
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 @@
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 @@
/* 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 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 @@
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 @@
* 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(®->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(®->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 @@
* 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 @@
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 @@
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 @@
}
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 @@
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 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);
