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>

1 files changed, 224 insertions, 26 deletions

diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 31123d4a6b9c..4e1e04dbc4ab 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 @@ 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);