dm: optimize use SRCU and RCU

This patch removes "io_lock" and "map_lock" in struct mapped_device and
"holders" in struct dm_table and replaces these mechanisms with
sleepable-rcu.

Previously, the code would call "dm_get_live_table" and "dm_table_put" to
get and release table. Now, the code is changed to call "dm_get_live_table"
and "dm_put_live_table". dm_get_live_table locks sleepable-rcu and
dm_put_live_table unlocks it.

dm_get_live_table_fast/dm_put_live_table_fast can be used instead of
dm_get_live_table/dm_put_live_table. These *_fast functions use
non-sleepable RCU, so the caller must not block between them.

If the code changes active or inactive dm table, it must call
dm_sync_table before destroying the old table.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

3 files changed, 175 insertions, 142 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 12f04868e899..f1b758675ec7 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -36,6 +36,14 @@ struct hash_cell {
         struct dm_table *new_map;
 };
 
+/*
+ * A dummy definition to make RCU happy.
+ * struct dm_table should never be dereferenced in this file.
+ */
+struct dm_table {
+        int undefined__;
+};
+
 struct vers_iter {
     size_t param_size;
     struct dm_target_versions *vers, *old_vers;
@@ -242,9 +250,10 @@ static int dm_hash_insert(const char *name, const char *uuid, struct mapped_devi
         return -EBUSY;
 }
 
-static void __hash_remove(struct hash_cell *hc)
+static struct dm_table *__hash_remove(struct hash_cell *hc)
 {
         struct dm_table *table;
+        int srcu_idx;
 
         /* remove from the dev hash */
         list_del(&hc->uuid_list);
@@ -253,16 +262,18 @@ static void __hash_remove(struct hash_cell *hc)
         dm_set_mdptr(hc->md, NULL);
         mutex_unlock(&dm_hash_cells_mutex);
 
-        table = dm_get_live_table(hc->md);
-        if (table) {
+        table = dm_get_live_table(hc->md, &srcu_idx);
+        if (table)
                 dm_table_event(table);
-                dm_table_put(table);
-        }
+        dm_put_live_table(hc->md, srcu_idx);
 
+        table = NULL;
         if (hc->new_map)
-                dm_table_destroy(hc->new_map);
+                table = hc->new_map;
         dm_put(hc->md);
         free_cell(hc);
+
+        return table;
 }
 
 static void dm_hash_remove_all(int keep_open_devices)
@@ -270,6 +281,7 @@ static void dm_hash_remove_all(int keep_open_devices)
         int i, dev_skipped;
         struct hash_cell *hc;
         struct mapped_device *md;
+        struct dm_table *t;
 
 retry:
         dev_skipped = 0;
@@ -287,10 +299,14 @@ retry:
                                 continue;
                         }
 
-                        __hash_remove(hc);
+                        t = __hash_remove(hc);
 
                         up_write(&_hash_lock);
 
+                        if (t) {
+                                dm_sync_table(md);
+                                dm_table_destroy(t);
+                        }
                         dm_put(md);
                         if (likely(keep_open_devices))
                                 dm_destroy(md);
@@ -356,6 +372,7 @@ static struct mapped_device *dm_hash_rename(struct dm_ioctl *param,
         struct dm_table *table;
         struct mapped_device *md;
         unsigned change_uuid = (param->flags & DM_UUID_FLAG) ? 1 : 0;
+        int srcu_idx;
 
         /*
          * duplicate new.
@@ -418,11 +435,10 @@ static struct mapped_device *dm_hash_rename(struct dm_ioctl *param,
         /*
          * Wake up any dm event waiters.
          */
-        table = dm_get_live_table(hc->md);
-        if (table) {
+        table = dm_get_live_table(hc->md, &srcu_idx);
+        if (table)
                 dm_table_event(table);
-                dm_table_put(table);
-        }
+        dm_put_live_table(hc->md, srcu_idx);
 
         if (!dm_kobject_uevent(hc->md, KOBJ_CHANGE, param->event_nr))
                 param->flags |= DM_UEVENT_GENERATED_FLAG;
@@ -620,11 +636,14 @@ static int check_name(const char *name)
  * _hash_lock without first calling dm_table_put, because dm_table_destroy
  * waits for this dm_table_put and could be called under this lock.
  */
-static struct dm_table *dm_get_inactive_table(struct mapped_device *md)
+static struct dm_table *dm_get_inactive_table(struct mapped_device *md, int *srcu_idx)
 {
         struct hash_cell *hc;
         struct dm_table *table = NULL;
 
+        /* increment rcu count, we don't care about the table pointer */
+        dm_get_live_table(md, srcu_idx);
+
         down_read(&_hash_lock);
         hc = dm_get_mdptr(md);
         if (!hc || hc->md != md) {
@@ -633,8 +652,6 @@ static struct dm_table *dm_get_inactive_table(struct mapped_device *md)
         }
 
         table = hc->new_map;
-        if (table)
-                dm_table_get(table);
 
 out:
         up_read(&_hash_lock);
@@ -643,10 +660,11 @@ out:
 }
 
 static struct dm_table *dm_get_live_or_inactive_table(struct mapped_device *md,
-                                                      struct dm_ioctl *param)
+                                                      struct dm_ioctl *param,
+                                                      int *srcu_idx)
 {
         return (param->flags & DM_QUERY_INACTIVE_TABLE_FLAG) ?
-                dm_get_inactive_table(md) : dm_get_live_table(md);
+                dm_get_inactive_table(md, srcu_idx) : dm_get_live_table(md, srcu_idx);
 }
 
 /*
@@ -657,6 +675,7 @@ static void __dev_status(struct mapped_device *md, struct dm_ioctl *param)
 {
         struct gendisk *disk = dm_disk(md);
         struct dm_table *table;
+        int srcu_idx;
 
         param->flags &= ~(DM_SUSPEND_FLAG | DM_READONLY_FLAG |
                           DM_ACTIVE_PRESENT_FLAG);
@@ -676,26 +695,27 @@ static void __dev_status(struct mapped_device *md, struct dm_ioctl *param)
         param->event_nr = dm_get_event_nr(md);
         param->target_count = 0;
 
-        table = dm_get_live_table(md);
+        table = dm_get_live_table(md, &srcu_idx);
         if (table) {
                 if (!(param->flags & DM_QUERY_INACTIVE_TABLE_FLAG)) {
                         if (get_disk_ro(disk))
                                 param->flags |= DM_READONLY_FLAG;
                         param->target_count = dm_table_get_num_targets(table);
                 }
-                dm_table_put(table);
 
                 param->flags |= DM_ACTIVE_PRESENT_FLAG;
         }
+        dm_put_live_table(md, srcu_idx);
 
         if (param->flags & DM_QUERY_INACTIVE_TABLE_FLAG) {
-                table = dm_get_inactive_table(md);
+                int srcu_idx;
+                table = dm_get_inactive_table(md, &srcu_idx);
                 if (table) {
                         if (!(dm_table_get_mode(table) & FMODE_WRITE))
                                 param->flags |= DM_READONLY_FLAG;
                         param->target_count = dm_table_get_num_targets(table);
-                        dm_table_put(table);
                 }
+                dm_put_live_table(md, srcu_idx);
         }
 }
 
@@ -796,6 +816,7 @@ static int dev_remove(struct dm_ioctl *param, size_t param_size)
         struct hash_cell *hc;
         struct mapped_device *md;
         int r;
+        struct dm_table *t;
 
         down_write(&_hash_lock);
         hc = __find_device_hash_cell(param);
@@ -819,9 +840,14 @@ static int dev_remove(struct dm_ioctl *param, size_t param_size)
                 return r;
         }
 
-        __hash_remove(hc);
+        t = __hash_remove(hc);
         up_write(&_hash_lock);
 
+        if (t) {
+                dm_sync_table(md);
+                dm_table_destroy(t);
+        }
+
         if (!dm_kobject_uevent(md, KOBJ_REMOVE, param->event_nr))
                 param->flags |= DM_UEVENT_GENERATED_FLAG;
 
@@ -986,6 +1012,7 @@ static int do_resume(struct dm_ioctl *param)
 
                 old_map = dm_swap_table(md, new_map);
                 if (IS_ERR(old_map)) {
+                        dm_sync_table(md);
                         dm_table_destroy(new_map);
                         dm_put(md);
                         return PTR_ERR(old_map);
@@ -1003,6 +1030,10 @@ static int do_resume(struct dm_ioctl *param)
                         param->flags |= DM_UEVENT_GENERATED_FLAG;
         }
 
+        /*
+         * Since dm_swap_table synchronizes RCU, nobody should be in
+         * read-side critical section already.
+         */
         if (old_map)
                 dm_table_destroy(old_map);
 
@@ -1125,6 +1156,7 @@ static int dev_wait(struct dm_ioctl *param, size_t param_size)
         int r = 0;
         struct mapped_device *md;
         struct dm_table *table;
+        int srcu_idx;
 
         md = find_device(param);
         if (!md)
@@ -1145,11 +1177,10 @@ static int dev_wait(struct dm_ioctl *param, size_t param_size)
          */
         __dev_status(md, param);
 
-        table = dm_get_live_or_inactive_table(md, param);
-        if (table) {
+        table = dm_get_live_or_inactive_table(md, param, &srcu_idx);
+        if (table)
                 retrieve_status(table, param, param_size);
-                dm_table_put(table);
-        }
+        dm_put_live_table(md, srcu_idx);
 
 out:
         dm_put(md);
@@ -1221,7 +1252,7 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
 {
         int r;
         struct hash_cell *hc;
-        struct dm_table *t;
+        struct dm_table *t, *old_map = NULL;
         struct mapped_device *md;
         struct target_type *immutable_target_type;
 
@@ -1277,14 +1308,14 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
         hc = dm_get_mdptr(md);
         if (!hc || hc->md != md) {
                 DMWARN("device has been removed from the dev hash table.");
-                dm_table_destroy(t);
                 up_write(&_hash_lock);
+                dm_table_destroy(t);
                 r = -ENXIO;
                 goto out;
         }
 
         if (hc->new_map)
-                dm_table_destroy(hc->new_map);
+                old_map = hc->new_map;
         hc->new_map = t;
         up_write(&_hash_lock);
 
@@ -1292,6 +1323,11 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
         __dev_status(md, param);
 
 out:
+        if (old_map) {
+                dm_sync_table(md);
+                dm_table_destroy(old_map);
+        }
+
         dm_put(md);
 
         return r;
@@ -1301,6 +1337,7 @@ static int table_clear(struct dm_ioctl *param, size_t param_size)
 {
         struct hash_cell *hc;
         struct mapped_device *md;
+        struct dm_table *old_map = NULL;
 
         down_write(&_hash_lock);
 
@@ -1312,7 +1349,7 @@ static int table_clear(struct dm_ioctl *param, size_t param_size)
         }
 
         if (hc->new_map) {
-                dm_table_destroy(hc->new_map);
+                old_map = hc->new_map;
                 hc->new_map = NULL;
         }
 
@@ -1321,6 +1358,10 @@ static int table_clear(struct dm_ioctl *param, size_t param_size)
         __dev_status(hc->md, param);
         md = hc->md;
         up_write(&_hash_lock);
+        if (old_map) {
+                dm_sync_table(md);
+                dm_table_destroy(old_map);
+        }
         dm_put(md);
 
         return 0;
@@ -1370,6 +1411,7 @@ static int table_deps(struct dm_ioctl *param, size_t param_size)
 {
         struct mapped_device *md;
         struct dm_table *table;
+        int srcu_idx;
 
         md = find_device(param);
         if (!md)
@@ -1377,11 +1419,10 @@ static int table_deps(struct dm_ioctl *param, size_t param_size)
 
         __dev_status(md, param);
 
-        table = dm_get_live_or_inactive_table(md, param);
-        if (table) {
+        table = dm_get_live_or_inactive_table(md, param, &srcu_idx);
+        if (table)
                 retrieve_deps(table, param, param_size);
-                dm_table_put(table);
-        }
+        dm_put_live_table(md, srcu_idx);
 
         dm_put(md);
 
@@ -1396,6 +1437,7 @@ static int table_status(struct dm_ioctl *param, size_t param_size)
 {
         struct mapped_device *md;
         struct dm_table *table;
+        int srcu_idx;
 
         md = find_device(param);
         if (!md)
@@ -1403,11 +1445,10 @@ static int table_status(struct dm_ioctl *param, size_t param_size)
 
         __dev_status(md, param);
 
-        table = dm_get_live_or_inactive_table(md, param);
-        if (table) {
+        table = dm_get_live_or_inactive_table(md, param, &srcu_idx);
+        if (table)
                 retrieve_status(table, param, param_size);
-                dm_table_put(table);
-        }
+        dm_put_live_table(md, srcu_idx);
 
         dm_put(md);
 
@@ -1443,6 +1484,7 @@ static int target_message(struct dm_ioctl *param, size_t param_size)
         struct dm_target_msg *tmsg = (void *) param + param->data_start;
         size_t maxlen;
         char *result = get_result_buffer(param, param_size, &maxlen);
+        int srcu_idx;
 
         md = find_device(param);
         if (!md)
@@ -1470,9 +1512,9 @@ static int target_message(struct dm_ioctl *param, size_t param_size)
         if (r <= 1)
                 goto out_argv;
 
-        table = dm_get_live_table(md);
+        table = dm_get_live_table(md, &srcu_idx);
         if (!table)
-                goto out_argv;
+                goto out_table;
 
         if (dm_deleting_md(md)) {
                 r = -ENXIO;
@@ -1491,7 +1533,7 @@ static int target_message(struct dm_ioctl *param, size_t param_size)
         }
 
  out_table:
-        dm_table_put(table);
+        dm_put_live_table(md, srcu_idx);
  out_argv:
         kfree(argv);
  out:
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 1ff252ab7d46..f221812b7dbc 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -26,22 +26,8 @@
 #define KEYS_PER_NODE (NODE_SIZE / sizeof(sector_t))
 #define CHILDREN_PER_NODE (KEYS_PER_NODE + 1)
 
-/*
- * The table has always exactly one reference from either mapped_device->map
- * or hash_cell->new_map. This reference is not counted in table->holders.
- * A pair of dm_create_table/dm_destroy_table functions is used for table
- * creation/destruction.
- *
- * Temporary references from the other code increase table->holders. A pair
- * of dm_table_get/dm_table_put functions is used to manipulate it.
- *
- * When the table is about to be destroyed, we wait for table->holders to
- * drop to zero.
- */
-
 struct dm_table {
         struct mapped_device *md;
-        atomic_t holders;
         unsigned type;
 
         /* btree table */
@@ -208,7 +194,6 @@ int dm_table_create(struct dm_table **result, fmode_t mode,
 
         INIT_LIST_HEAD(&t->devices);
         INIT_LIST_HEAD(&t->target_callbacks);
-        atomic_set(&t->holders, 0);
 
         if (!num_targets)
                 num_targets = KEYS_PER_NODE;
@@ -246,10 +231,6 @@ void dm_table_destroy(struct dm_table *t)
         if (!t)
                 return;
 
-        while (atomic_read(&t->holders))
-                msleep(1);
-        smp_mb();
-
         /* free the indexes */
         if (t->depth >= 2)
                 vfree(t->index[t->depth - 2]);
@@ -274,22 +255,6 @@ void dm_table_destroy(struct dm_table *t)
         kfree(t);
 }
 
-void dm_table_get(struct dm_table *t)
-{
-        atomic_inc(&t->holders);
-}
-EXPORT_SYMBOL(dm_table_get);
-
-void dm_table_put(struct dm_table *t)
-{
-        if (!t)
-                return;
-
-        smp_mb__before_atomic_dec();
-        atomic_dec(&t->holders);
-}
-EXPORT_SYMBOL(dm_table_put);
-
 /*
  * Checks to see if we need to extend highs or targets.
  */
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 33f20103d8d5..ecff83f5b53a 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -117,12 +117,19 @@ EXPORT_SYMBOL_GPL(dm_get_rq_mapinfo);
 #define DMF_MERGE_IS_OPTIONAL 6
 
 /*
+ * A dummy definition to make RCU happy.
+ * struct dm_table should never be dereferenced in this file.
+ */
+struct dm_table {
+        int undefined__;
+};
+
+/*
  * Work processed by per-device workqueue.
  */
 struct mapped_device {
-        struct rw_semaphore io_lock;
+        struct srcu_struct io_barrier;
         struct mutex suspend_lock;
-        rwlock_t map_lock;
         atomic_t holders;
         atomic_t open_count;
 
@@ -156,6 +163,8 @@ struct mapped_device {
 
         /*
          * The current mapping.
+         * Use dm_get_live_table{_fast} or take suspend_lock for
+         * dereference.
          */
         struct dm_table *map;
 
@@ -386,12 +395,14 @@ static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode,
                         unsigned int cmd, unsigned long arg)
 {
         struct mapped_device *md = bdev->bd_disk->private_data;
+        int srcu_idx;
         struct dm_table *map;
         struct dm_target *tgt;
         int r = -ENOTTY;
 
 retry:
-        map = dm_get_live_table(md);
+        map = dm_get_live_table(md, &srcu_idx);
+
         if (!map || !dm_table_get_size(map))
                 goto out;
 
@@ -410,7 +421,7 @@ retry:
                 r = tgt->type->ioctl(tgt, cmd, arg);
 
 out:
-        dm_table_put(map);
+        dm_put_live_table(md, srcu_idx);
 
         if (r == -ENOTCONN) {
                 msleep(10);
@@ -509,20 +520,39 @@ static void queue_io(struct mapped_device *md, struct bio *bio)
 /*
  * Everyone (including functions in this file), should use this
  * function to access the md->map field, and make sure they call
- * dm_table_put() when finished.
+ * dm_put_live_table() when finished.
  */
-struct dm_table *dm_get_live_table(struct mapped_device *md)
+struct dm_table *dm_get_live_table(struct mapped_device *md, int *srcu_idx) __acquires(md->io_barrier)
 {
-        struct dm_table *t;
-        unsigned long flags;
+        *srcu_idx = srcu_read_lock(&md->io_barrier);
+
+        return srcu_dereference(md->map, &md->io_barrier);
+}
 
-        read_lock_irqsave(&md->map_lock, flags);
-        t = md->map;
-        if (t)
-                dm_table_get(t);
-        read_unlock_irqrestore(&md->map_lock, flags);
+void dm_put_live_table(struct mapped_device *md, int srcu_idx) __releases(md->io_barrier)
+{
+        srcu_read_unlock(&md->io_barrier, srcu_idx);
+}
+
+void dm_sync_table(struct mapped_device *md)
+{
+        synchronize_srcu(&md->io_barrier);
+        synchronize_rcu_expedited();
+}
+
+/*
+ * A fast alternative to dm_get_live_table/dm_put_live_table.
+ * The caller must not block between these two functions.
+ */
+static struct dm_table *dm_get_live_table_fast(struct mapped_device *md) __acquires(RCU)
+{
+        rcu_read_lock();
+        return rcu_dereference(md->map);
+}
 
-        return t;
+static void dm_put_live_table_fast(struct mapped_device *md) __releases(RCU)
+{
+        rcu_read_unlock();
 }
 
 /*
@@ -1356,17 +1386,18 @@ static int __split_and_process_non_flush(struct clone_info *ci)
 /*
  * Entry point to split a bio into clones and submit them to the targets.
  */
-static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
+static void __split_and_process_bio(struct mapped_device *md,
+                                    struct dm_table *map, struct bio *bio)
 {
         struct clone_info ci;
         int error = 0;
 
-        ci.map = dm_get_live_table(md);
-        if (unlikely(!ci.map)) {
+        if (unlikely(!map)) {
                 bio_io_error(bio);
                 return;
         }
 
+        ci.map = map;
         ci.md = md;
         ci.io = alloc_io(md);
         ci.io->error = 0;
@@ -1393,7 +1424,6 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
 
         /* drop the extra reference count */
         dec_pending(ci.io, error);
-        dm_table_put(ci.map);
 }
 /*-----------------------------------------------------------------
  * CRUD END
@@ -1404,7 +1434,7 @@ static int dm_merge_bvec(struct request_queue *q,
                          struct bio_vec *biovec)
 {
         struct mapped_device *md = q->queuedata;
-        struct dm_table *map = dm_get_live_table(md);
+        struct dm_table *map = dm_get_live_table_fast(md);
         struct dm_target *ti;
         sector_t max_sectors;
         int max_size = 0;
@@ -1414,7 +1444,7 @@ static int dm_merge_bvec(struct request_queue *q,
 
         ti = dm_table_find_target(map, bvm->bi_sector);
         if (!dm_target_is_valid(ti))
-                goto out_table;
+                goto out;
 
         /*
          * Find maximum amount of I/O that won't need splitting
@@ -1443,10 +1473,8 @@ static int dm_merge_bvec(struct request_queue *q,
 
                 max_size = 0;
 
-out_table:
-        dm_table_put(map);
-
 out:
+        dm_put_live_table_fast(md);
         /*
          * Always allow an entire first page
          */
@@ -1465,8 +1493,10 @@ static void _dm_request(struct request_queue *q, struct bio *bio)
         int rw = bio_data_dir(bio);
         struct mapped_device *md = q->queuedata;
         int cpu;
+        int srcu_idx;
+        struct dm_table *map;
 
-        down_read(&md->io_lock);
+        map = dm_get_live_table(md, &srcu_idx);
 
         cpu = part_stat_lock();
         part_stat_inc(cpu, &dm_disk(md)->part0, ios[rw]);
@@ -1475,7 +1505,7 @@ static void _dm_request(struct request_queue *q, struct bio *bio)
 
         /* if we're suspended, we have to queue this io for later */
         if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
-                up_read(&md->io_lock);
+                dm_put_live_table(md, srcu_idx);
 
                 if (bio_rw(bio) != READA)
                         queue_io(md, bio);
@@ -1484,8 +1514,8 @@ static void _dm_request(struct request_queue *q, struct bio *bio)
                 return;
         }
 
-        __split_and_process_bio(md, bio);
-        up_read(&md->io_lock);
+        __split_and_process_bio(md, map, bio);
+        dm_put_live_table(md, srcu_idx);
         return;
 }
 
@@ -1671,7 +1701,8 @@ static struct request *dm_start_request(struct mapped_device *md, struct request
 static void dm_request_fn(struct request_queue *q)
 {
         struct mapped_device *md = q->queuedata;
-        struct dm_table *map = dm_get_live_table(md);
+        int srcu_idx;
+        struct dm_table *map = dm_get_live_table(md, &srcu_idx);
         struct dm_target *ti;
         struct request *rq, *clone;
         sector_t pos;
@@ -1726,7 +1757,7 @@ requeued:
 delay_and_out:
         blk_delay_queue(q, HZ / 10);
 out:
-        dm_table_put(map);
+        dm_put_live_table(md, srcu_idx);
 }
 
 int dm_underlying_device_busy(struct request_queue *q)
@@ -1739,14 +1770,14 @@ static int dm_lld_busy(struct request_queue *q)
 {
         int r;
         struct mapped_device *md = q->queuedata;
-        struct dm_table *map = dm_get_live_table(md);
+        struct dm_table *map = dm_get_live_table_fast(md);
 
         if (!map || test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))
                 r = 1;
         else
                 r = dm_table_any_busy_target(map);
 
-        dm_table_put(map);
+        dm_put_live_table_fast(md);
 
         return r;
 }
@@ -1758,7 +1789,7 @@ static int dm_any_congested(void *congested_data, int bdi_bits)
         struct dm_table *map;
 
         if (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) {
-                map = dm_get_live_table(md);
+                map = dm_get_live_table_fast(md);
                 if (map) {
                         /*
                          * Request-based dm cares about only own queue for
@@ -1769,9 +1800,8 @@ static int dm_any_congested(void *congested_data, int bdi_bits)
                                     bdi_bits;
                         else
                                 r = dm_table_any_congested(map, bdi_bits);
-
-                        dm_table_put(map);
                 }
+                dm_put_live_table_fast(md);
         }
 
         return r;
@@ -1876,12 +1906,14 @@ static struct mapped_device *alloc_dev(int minor)
         if (r < 0)
                 goto bad_minor;
 
+        r = init_srcu_struct(&md->io_barrier);
+        if (r < 0)
+                goto bad_io_barrier;
+
         md->type = DM_TYPE_NONE;
-        init_rwsem(&md->io_lock);
         mutex_init(&md->suspend_lock);
         mutex_init(&md->type_lock);
         spin_lock_init(&md->deferred_lock);
-        rwlock_init(&md->map_lock);
         atomic_set(&md->holders, 1);
         atomic_set(&md->open_count, 0);
         atomic_set(&md->event_nr, 0);
@@ -1944,6 +1976,8 @@ bad_thread:
 bad_disk:
         blk_cleanup_queue(md->queue);
 bad_queue:
+        cleanup_srcu_struct(&md->io_barrier);
+bad_io_barrier:
         free_minor(minor);
 bad_minor:
         module_put(THIS_MODULE);
@@ -1967,6 +2001,7 @@ static void free_dev(struct mapped_device *md)
                 bioset_free(md->bs);
         blk_integrity_unregister(md->disk);
         del_gendisk(md->disk);
+        cleanup_srcu_struct(&md->io_barrier);
         free_minor(minor);
 
         spin_lock(&_minor_lock);
@@ -2109,7 +2144,6 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
         struct dm_table *old_map;
         struct request_queue *q = md->queue;
         sector_t size;
-        unsigned long flags;
         int merge_is_optional;
 
         size = dm_table_get_size(t);
@@ -2138,9 +2172,8 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
 
         merge_is_optional = dm_table_merge_is_optional(t);
 
-        write_lock_irqsave(&md->map_lock, flags);
         old_map = md->map;
-        md->map = t;
+        rcu_assign_pointer(md->map, t);
         md->immutable_target_type = dm_table_get_immutable_target_type(t);
 
         dm_table_set_restrictions(t, q, limits);
@@ -2148,7 +2181,7 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
                 set_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
         else
                 clear_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
-        write_unlock_irqrestore(&md->map_lock, flags);
+        dm_sync_table(md);
 
         return old_map;
 }
@@ -2159,15 +2192,13 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
 static struct dm_table *__unbind(struct mapped_device *md)
 {
         struct dm_table *map = md->map;
-        unsigned long flags;
 
         if (!map)
                 return NULL;
 
         dm_table_event_callback(map, NULL, NULL);
-        write_lock_irqsave(&md->map_lock, flags);
-        md->map = NULL;
-        write_unlock_irqrestore(&md->map_lock, flags);
+        rcu_assign_pointer(md->map, NULL);
+        dm_sync_table(md);
 
         return map;
 }
@@ -2319,11 +2350,12 @@ EXPORT_SYMBOL_GPL(dm_device_name);
 static void __dm_destroy(struct mapped_device *md, bool wait)
 {
         struct dm_table *map;
+        int srcu_idx;
 
         might_sleep();
 
         spin_lock(&_minor_lock);
-        map = dm_get_live_table(md);
+        map = dm_get_live_table(md, &srcu_idx);
         idr_replace(&_minor_idr, MINOR_ALLOCED, MINOR(disk_devt(dm_disk(md))));
         set_bit(DMF_FREEING, &md->flags);
         spin_unlock(&_minor_lock);
@@ -2333,6 +2365,9 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
                 dm_table_postsuspend_targets(map);
         }
 
+        /* dm_put_live_table must be before msleep, otherwise deadlock is possible */
+        dm_put_live_table(md, srcu_idx);
+
         /*
          * Rare, but there may be I/O requests still going to complete,
          * for example.  Wait for all references to disappear.
@@ -2347,7 +2382,6 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
                        dm_device_name(md), atomic_read(&md->holders));
 
         dm_sysfs_exit(md);
-        dm_table_put(map);
         dm_table_destroy(__unbind(md));
         free_dev(md);
 }
@@ -2404,8 +2438,10 @@ static void dm_wq_work(struct work_struct *work)
         struct mapped_device *md = container_of(work, struct mapped_device,
                                                 work);
         struct bio *c;
+        int srcu_idx;
+        struct dm_table *map;
 
-        down_read(&md->io_lock);
+        map = dm_get_live_table(md, &srcu_idx);
 
         while (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) {
                 spin_lock_irq(&md->deferred_lock);
@@ -2415,17 +2451,13 @@ static void dm_wq_work(struct work_struct *work)
                 if (!c)
                         break;
 
-                up_read(&md->io_lock);
-
                 if (dm_request_based(md))
                         generic_make_request(c);
                 else
-                        __split_and_process_bio(md, c);
-
-                down_read(&md->io_lock);
+                        __split_and_process_bio(md, map, c);
         }
 
-        up_read(&md->io_lock);
+        dm_put_live_table(md, srcu_idx);
 }
 
 static void dm_queue_flush(struct mapped_device *md)
@@ -2457,10 +2489,10 @@ struct dm_table *dm_swap_table(struct mapped_device *md, struct dm_table *table)
          * reappear.
          */
         if (dm_table_has_no_data_devices(table)) {
-                live_map = dm_get_live_table(md);
+                live_map = dm_get_live_table_fast(md);
                 if (live_map)
                         limits = md->queue->limits;
-                dm_table_put(live_map);
+                dm_put_live_table_fast(md);
         }
 
         if (!live_map) {
@@ -2540,7 +2572,7 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
                 goto out_unlock;
         }
 
-        map = dm_get_live_table(md);
+        map = md->map;
 
         /*
          * DMF_NOFLUSH_SUSPENDING must be set before presuspend.
@@ -2561,7 +2593,7 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
         if (!noflush && do_lockfs) {
                 r = lock_fs(md);
                 if (r)
-                        goto out;
+                        goto out_unlock;
         }
 
         /*
@@ -2576,9 +2608,8 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
          * (dm_wq_work), we set BMF_BLOCK_IO_FOR_SUSPEND and call
          * flush_workqueue(md->wq).
          */
-        down_write(&md->io_lock);
         set_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
-        up_write(&md->io_lock);
+        synchronize_srcu(&md->io_barrier);
 
         /*
          * Stop md->queue before flushing md->wq in case request-based
@@ -2596,10 +2627,9 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
          */
         r = dm_wait_for_completion(md, TASK_INTERRUPTIBLE);
 
-        down_write(&md->io_lock);
         if (noflush)
                 clear_bit(DMF_NOFLUSH_SUSPENDING, &md->flags);
-        up_write(&md->io_lock);
+        synchronize_srcu(&md->io_barrier);
 
         /* were we interrupted ? */
         if (r < 0) {
@@ -2609,7 +2639,7 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
                         start_queue(md->queue);
 
                 unlock_fs(md);
-                goto out; /* pushback list is already flushed, so skip flush */
+                goto out_unlock; /* pushback list is already flushed, so skip flush */
         }
 
         /*
@@ -2622,9 +2652,6 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
 
         dm_table_postsuspend_targets(map);
 
-out:
-        dm_table_put(map);
-
 out_unlock:
         mutex_unlock(&md->suspend_lock);
         return r;
@@ -2639,7 +2666,7 @@ int dm_resume(struct mapped_device *md)
         if (!dm_suspended_md(md))
                 goto out;
 
-        map = dm_get_live_table(md);
+        map = md->map;
         if (!map || !dm_table_get_size(map))
                 goto out;
 
@@ -2663,7 +2690,6 @@ int dm_resume(struct mapped_device *md)
 
         r = 0;
 out:
-        dm_table_put(map);
         mutex_unlock(&md->suspend_lock);
 
         return r;