dm: allow active and inactive tables to share dm_devs

Until this change, when loading a new DM table, DM core would re-open
all of the devices in the DM table.  Now, DM core will avoid redundant
device opens (and closes when destroying the old table) if the old
table already has a device open using the same mode.  This is achieved
by managing reference counts on the table_devices that DM core now
stores in the mapped_device structure (rather than in the dm_table
structure).  So a mapped_device's active and inactive dm_tables' dm_dev
lists now just point to the dm_devs stored in the mapped_device's
table_devices list.

This improvement in DM core's device reference counting has the
side-effect of fixing a long-standing limitation of the multipath
target: a DM multipath table couldn't include any paths that were unusable
(failed).  For example: if all paths have failed and you add a new,
working, path to the table; you can't use it since the table load would
fail due to it still containing failed paths.  Now a re-load of a
multipath table can include failed devices and when those devices become
active again they can be used instantly.

The device list code in dm.c isn't a straight copy/paste from the code in
dm-table.c, but it's very close (aside from some variable renames).  One
subtle difference is that find_table_device for the tables_devices list
will only match devices with the same name and mode.  This is because we
don't want to upgrade a device's mode in the active table when an
inactive table is loaded.

Access to the mapped_device structure's tables_devices list requires a
mutex (tables_devices_lock), so that tables cannot be created and
destroyed concurrently.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

5 files changed, 167 insertions, 72 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 51521429fb59..0be9381365d7 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1418,7 +1418,7 @@ static void retrieve_deps(struct dm_table *table,
         deps->count = count;
         count = 0;
         list_for_each_entry (dd, dm_table_get_devices(table), list)
-                deps->dev[count++] = huge_encode_dev(dd->dm_dev.bdev->bd_dev);
+                deps->dev[count++] = huge_encode_dev(dd->dm_dev->bdev->bd_dev);
 
         param->data_size = param->data_start + needed;
 }
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index f9c6cb8dbcf8..b2bd1ebf4562 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -210,15 +210,16 @@ int dm_table_create(struct dm_table **result, fmode_t mode,
         return 0;
 }
 
-static void free_devices(struct list_head *devices)
+static void free_devices(struct list_head *devices, struct mapped_device *md)
 {
         struct list_head *tmp, *next;
 
         list_for_each_safe(tmp, next, devices) {
                 struct dm_dev_internal *dd =
                     list_entry(tmp, struct dm_dev_internal, list);
-                DMWARN("dm_table_destroy: dm_put_device call missing for %s",
-                       dd->dm_dev.name);
+                DMWARN("%s: dm_table_destroy: dm_put_device call missing for %s",
+                       dm_device_name(md), dd->dm_dev->name);
+                dm_put_table_device(md, dd->dm_dev);
                 kfree(dd);
         }
 }
@@ -247,7 +248,7 @@ void dm_table_destroy(struct dm_table *t)
         vfree(t->highs);
 
         /* free the device list */
-        free_devices(&t->devices);
+        free_devices(&t->devices, t->md);
 
         dm_free_md_mempools(t->mempools);
 
@@ -262,53 +263,13 @@ static struct dm_dev_internal *find_device(struct list_head *l, dev_t dev)
         struct dm_dev_internal *dd;
 
         list_for_each_entry (dd, l, list)
-                if (dd->dm_dev.bdev->bd_dev == dev)
+                if (dd->dm_dev->bdev->bd_dev == dev)
                         return dd;
 
         return NULL;
 }
 
 /*
- * Open a device so we can use it as a map destination.
- */
-static int open_dev(struct dm_dev_internal *d, dev_t dev,
-                    struct mapped_device *md)
-{
-        static char *_claim_ptr = "I belong to device-mapper";
-        struct block_device *bdev;
-
-        int r;
-
-        BUG_ON(d->dm_dev.bdev);
-
-        bdev = blkdev_get_by_dev(dev, d->dm_dev.mode | FMODE_EXCL, _claim_ptr);
-        if (IS_ERR(bdev))
-                return PTR_ERR(bdev);
-
-        r = bd_link_disk_holder(bdev, dm_disk(md));
-        if (r) {
-                blkdev_put(bdev, d->dm_dev.mode | FMODE_EXCL);
-                return r;
-        }
-
-        d->dm_dev.bdev = bdev;
-        return 0;
-}
-
-/*
- * Close a device that we've been using.
- */
-static void close_dev(struct dm_dev_internal *d, struct mapped_device *md)
-{
-        if (!d->dm_dev.bdev)
-                return;
-
-        bd_unlink_disk_holder(d->dm_dev.bdev, dm_disk(md));
-        blkdev_put(d->dm_dev.bdev, d->dm_dev.mode | FMODE_EXCL);
-        d->dm_dev.bdev = NULL;
-}
-
-/*
  * If possible, this checks an area of a destination device is invalid.
  */
 static int device_area_is_invalid(struct dm_target *ti, struct dm_dev *dev,
@@ -386,19 +347,17 @@ static int upgrade_mode(struct dm_dev_internal *dd, fmode_t new_mode,
                         struct mapped_device *md)
 {
         int r;
-        struct dm_dev_internal dd_new, dd_old;
+        struct dm_dev *old_dev, *new_dev;
 
-        dd_new = dd_old = *dd;
+        old_dev = dd->dm_dev;
 
-        dd_new.dm_dev.mode |= new_mode;
-        dd_new.dm_dev.bdev = NULL;
-
-        r = open_dev(&dd_new, dd->dm_dev.bdev->bd_dev, md);
+        r = dm_get_table_device(md, dd->dm_dev->bdev->bd_dev,
+                                dd->dm_dev->mode | new_mode, &new_dev);
         if (r)
                 return r;
 
-        dd->dm_dev.mode |= new_mode;
-        close_dev(&dd_old, md);
+        dd->dm_dev = new_dev;
+        dm_put_table_device(md, old_dev);
 
         return 0;
 }
@@ -440,27 +399,22 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
                 if (!dd)
                         return -ENOMEM;
 
-                dd->dm_dev.mode = mode;
-                dd->dm_dev.bdev = NULL;
-
-                if ((r = open_dev(dd, dev, t->md))) {
+                if ((r = dm_get_table_device(t->md, dev, mode, &dd->dm_dev))) {
                         kfree(dd);
                         return r;
                 }
 
-                format_dev_t(dd->dm_dev.name, dev);
-
                 atomic_set(&dd->count, 0);
                 list_add(&dd->list, &t->devices);
 
-        } else if (dd->dm_dev.mode != (mode | dd->dm_dev.mode)) {
+        } else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
                 r = upgrade_mode(dd, mode, t->md);
                 if (r)
                         return r;
         }
         atomic_inc(&dd->count);
 
-        *result = &dd->dm_dev;
+        *result = dd->dm_dev;
         return 0;
 }
 EXPORT_SYMBOL(dm_get_device);
@@ -505,11 +459,23 @@ static int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
  */
 void dm_put_device(struct dm_target *ti, struct dm_dev *d)
 {
-        struct dm_dev_internal *dd = container_of(d, struct dm_dev_internal,
-                                                  dm_dev);
+        int found = 0;
+        struct list_head *devices = &ti->table->devices;
+        struct dm_dev_internal *dd;
 
+        list_for_each_entry(dd, devices, list) {
+                if (dd->dm_dev == d) {
+                        found = 1;
+                        break;
+                }
+        }
+        if (!found) {
+                DMWARN("%s: device %s not in table devices list",
+                       dm_device_name(ti->table->md), d->name);
+                return;
+        }
         if (atomic_dec_and_test(&dd->count)) {
-                close_dev(dd, ti->table->md);
+                dm_put_table_device(ti->table->md, d);
                 list_del(&dd->list);
                 kfree(dd);
         }
@@ -906,7 +872,7 @@ static int dm_table_set_type(struct dm_table *t)
         /* Non-request-stackable devices can't be used for request-based dm */
         devices = dm_table_get_devices(t);
         list_for_each_entry(dd, devices, list) {
-                if (!blk_queue_stackable(bdev_get_queue(dd->dm_dev.bdev))) {
+                if (!blk_queue_stackable(bdev_get_queue(dd->dm_dev->bdev))) {
                         DMWARN("table load rejected: including"
                                " non-request-stackable devices");
                         return -EINVAL;
@@ -1043,7 +1009,7 @@ static struct gendisk * dm_table_get_integrity_disk(struct dm_table *t,
         struct gendisk *prev_disk = NULL, *template_disk = NULL;
 
         list_for_each_entry(dd, devices, list) {
-                template_disk = dd->dm_dev.bdev->bd_disk;
+                template_disk = dd->dm_dev->bdev->bd_disk;
                 if (!blk_get_integrity(template_disk))
                         goto no_integrity;
                 if (!match_all && !blk_integrity_is_initialized(template_disk))
@@ -1629,7 +1595,7 @@ int dm_table_any_congested(struct dm_table *t, int bdi_bits)
         int r = 0;
 
         list_for_each_entry(dd, devices, list) {
-                struct request_queue *q = bdev_get_queue(dd->dm_dev.bdev);
+                struct request_queue *q = bdev_get_queue(dd->dm_dev->bdev);
                 char b[BDEVNAME_SIZE];
 
                 if (likely(q))
@@ -1637,7 +1603,7 @@ int dm_table_any_congested(struct dm_table *t, int bdi_bits)
                 else
                         DMWARN_LIMIT("%s: any_congested: nonexistent device %s",
                                      dm_device_name(t->md),
-                                     bdevname(dd->dm_dev.bdev, b));
+                                     bdevname(dd->dm_dev->bdev, b));
         }
 
         list_for_each_entry(cb, &t->target_callbacks, list)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 56a2c74c9a3f..58f3927fd7cc 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -142,6 +142,9 @@ struct mapped_device {
          */
         struct dm_table *map;
 
+        struct list_head table_devices;
+        struct mutex table_devices_lock;
+
         unsigned long flags;
 
         struct request_queue *queue;
@@ -212,6 +215,12 @@ struct dm_md_mempools {
         struct bio_set *bs;
 };
 
+struct table_device {
+        struct list_head list;
+        atomic_t count;
+        struct dm_dev dm_dev;
+};
+
 #define RESERVED_BIO_BASED_IOS          16
 #define RESERVED_REQUEST_BASED_IOS      256
 #define RESERVED_MAX_IOS                1024
@@ -670,6 +679,120 @@ static void dm_put_live_table_fast(struct mapped_device *md) __releases(RCU)
 }
 
 /*
+ * Open a table device so we can use it as a map destination.
+ */
+static int open_table_device(struct table_device *td, dev_t dev,
+                             struct mapped_device *md)
+{
+        static char *_claim_ptr = "I belong to device-mapper";
+        struct block_device *bdev;
+
+        int r;
+
+        BUG_ON(td->dm_dev.bdev);
+
+        bdev = blkdev_get_by_dev(dev, td->dm_dev.mode | FMODE_EXCL, _claim_ptr);
+        if (IS_ERR(bdev))
+                return PTR_ERR(bdev);
+
+        r = bd_link_disk_holder(bdev, dm_disk(md));
+        if (r) {
+                blkdev_put(bdev, td->dm_dev.mode | FMODE_EXCL);
+                return r;
+        }
+
+        td->dm_dev.bdev = bdev;
+        return 0;
+}
+
+/*
+ * Close a table device that we've been using.
+ */
+static void close_table_device(struct table_device *td, struct mapped_device *md)
+{
+        if (!td->dm_dev.bdev)
+                return;
+
+        bd_unlink_disk_holder(td->dm_dev.bdev, dm_disk(md));
+        blkdev_put(td->dm_dev.bdev, td->dm_dev.mode | FMODE_EXCL);
+        td->dm_dev.bdev = NULL;
+}
+
+static struct table_device *find_table_device(struct list_head *l, dev_t dev,
+                                              fmode_t mode) {
+        struct table_device *td;
+
+        list_for_each_entry(td, l, list)
+                if (td->dm_dev.bdev->bd_dev == dev && td->dm_dev.mode == mode)
+                        return td;
+
+        return NULL;
+}
+
+int dm_get_table_device(struct mapped_device *md, dev_t dev, fmode_t mode,
+                        struct dm_dev **result) {
+        int r;
+        struct table_device *td;
+
+        mutex_lock(&md->table_devices_lock);
+        td = find_table_device(&md->table_devices, dev, mode);
+        if (!td) {
+                td = kmalloc(sizeof(*td), GFP_KERNEL);
+                if (!td) {
+                        mutex_unlock(&md->table_devices_lock);
+                        return -ENOMEM;
+                }
+
+                td->dm_dev.mode = mode;
+                td->dm_dev.bdev = NULL;
+
+                if ((r = open_table_device(td, dev, md))) {
+                        mutex_unlock(&md->table_devices_lock);
+                        kfree(td);
+                        return r;
+                }
+
+                format_dev_t(td->dm_dev.name, dev);
+
+                atomic_set(&td->count, 0);
+                list_add(&td->list, &md->table_devices);
+        }
+        atomic_inc(&td->count);
+        mutex_unlock(&md->table_devices_lock);
+
+        *result = &td->dm_dev;
+        return 0;
+}
+EXPORT_SYMBOL_GPL(dm_get_table_device);
+
+void dm_put_table_device(struct mapped_device *md, struct dm_dev *d)
+{
+        struct table_device *td = container_of(d, struct table_device, dm_dev);
+
+        mutex_lock(&md->table_devices_lock);
+        if (atomic_dec_and_test(&td->count)) {
+                close_table_device(td, md);
+                list_del(&td->list);
+                kfree(td);
+        }
+        mutex_unlock(&md->table_devices_lock);
+}
+EXPORT_SYMBOL(dm_put_table_device);
+
+static void free_table_devices(struct list_head *devices)
+{
+        struct list_head *tmp, *next;
+
+        list_for_each_safe(tmp, next, devices) {
+                struct table_device *td = list_entry(tmp, struct table_device, list);
+
+                DMWARN("dm_destroy: %s still exists with %d references",
+                       td->dm_dev.name, atomic_read(&td->count));
+                kfree(td);
+        }
+}
+
+/*
  * Get the geometry associated with a dm device
  */
 int dm_get_geometry(struct mapped_device *md, struct hd_geometry *geo)
@@ -1944,12 +2067,14 @@ static struct mapped_device *alloc_dev(int minor)
         md->type = DM_TYPE_NONE;
         mutex_init(&md->suspend_lock);
         mutex_init(&md->type_lock);
+        mutex_init(&md->table_devices_lock);
         spin_lock_init(&md->deferred_lock);
         atomic_set(&md->holders, 1);
         atomic_set(&md->open_count, 0);
         atomic_set(&md->event_nr, 0);
         atomic_set(&md->uevent_seq, 0);
         INIT_LIST_HEAD(&md->uevent_list);
+        INIT_LIST_HEAD(&md->table_devices);
         spin_lock_init(&md->uevent_lock);
 
         md->queue = blk_alloc_queue(GFP_KERNEL);
@@ -2035,6 +2160,7 @@ static void free_dev(struct mapped_device *md)
         blk_integrity_unregister(md->disk);
         del_gendisk(md->disk);
         cleanup_srcu_struct(&md->io_barrier);
+        free_table_devices(&md->table_devices);
         free_minor(minor);
 
         spin_lock(&_minor_lock);
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index e81d2152fa68..988c7fb7b145 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -44,7 +44,7 @@
 struct dm_dev_internal {
         struct list_head list;
         atomic_t count;
-        struct dm_dev dm_dev;
+        struct dm_dev *dm_dev;
 };
 
 struct dm_table;
@@ -188,6 +188,9 @@ int dm_cancel_deferred_remove(struct mapped_device *md);
 int dm_request_based(struct mapped_device *md);
 sector_t dm_get_size(struct mapped_device *md);
 struct request_queue *dm_get_md_queue(struct mapped_device *md);
+int dm_get_table_device(struct mapped_device *md, dev_t dev, fmode_t mode,
+                        struct dm_dev **result);
+void dm_put_table_device(struct mapped_device *md, struct dm_dev *d);
 struct dm_stats *dm_get_stats(struct mapped_device *md);
 
 int dm_kobject_uevent(struct mapped_device *md, enum kobject_action action,
diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index c8a4302093a3..3315ab21f728 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -267,9 +267,9 @@ enum {
 #define DM_DEV_SET_GEOMETRY     _IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)
 
 #define DM_VERSION_MAJOR        4
-#define DM_VERSION_MINOR        27
+#define DM_VERSION_MINOR        28
 #define DM_VERSION_PATCHLEVEL   0
-#define DM_VERSION_EXTRA        "-ioctl (2013-10-30)"
+#define DM_VERSION_EXTRA        "-ioctl (2014-09-17)"
 
 /* Status bits */
 #define DM_READONLY_FLAG        (1 << 0) /* In/Out */