Revert "dm: fix a race condition in retrieve_deps"

This reverts commit f6007dc.

Commit f6007dc ("dm: fix a race condition in retrieve_deps") was
added to fix a race between retrieving the list of dm table devices and
multipath_message() modifying the list of table devices. But Commit
a48f6b8 ("dm mpath: don't call dm_get_device in multipath_message")
removed the call to dm_get_device() from multipath_message(). After that
commit, the only calls to dm_get_device() and dm_put_device() are in
target constructors and destructors, so the race with retrieve_deps() is
no longer possible.

Suggested-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Author: bmarzins

drivers/md/dm-core.h

@@ -215,7 +215,6 @@ struct dm_table {
 
 	/* a list of devices used by this table */
 	struct list_head devices;
-	struct rw_semaphore devices_lock;
 
 	/* events get handed up using this callback */
 	void (*event_fn)(void *data);

drivers/md/dm-ioctl.c

@@ -1648,8 +1648,6 @@ static void retrieve_deps(struct dm_table *table,
 	struct dm_dev_internal *dd;
 	struct dm_target_deps *deps;
 
-	down_read(&table->devices_lock);
-
 	deps = get_result_buffer(param, param_size, &len);
 
 	/*
@@ -1664,7 +1662,7 @@ static void retrieve_deps(struct dm_table *table,
 	needed = struct_size(deps, dev, count);
 	if (len < needed) {
 		param->flags |= DM_BUFFER_FULL_FLAG;
-		goto out;
+		return;
 	}
 
 	/*
@@ -1676,9 +1674,6 @@ static void retrieve_deps(struct dm_table *table,
 		deps->dev[count++] = huge_encode_dev(dd->dm_dev->bdev->bd_dev);
 
 	param->data_size = param->data_start + needed;
-
-out:
-	up_read(&table->devices_lock);
 }
 
 static int table_deps(struct file *filp, struct dm_ioctl *param, size_t param_size)

drivers/md/dm-table.c

@@ -139,7 +139,6 @@ int dm_table_create(struct dm_table **result, blk_mode_t mode,
 		return -ENOMEM;
 
 	INIT_LIST_HEAD(&t->devices);
-	init_rwsem(&t->devices_lock);
 
 	if (!num_targets)
 		num_targets = KEYS_PER_NODE;
@@ -380,20 +379,16 @@ int dm_get_device(struct dm_target *ti, const char *path, blk_mode_t mode,
 	if (dev == disk_devt(t->md->disk))
 		return -EINVAL;
 
-	down_write(&t->devices_lock);
-
 	dd = find_device(&t->devices, dev);
 	if (!dd) {
 		dd = kmalloc(sizeof(*dd), GFP_KERNEL);
-		if (!dd) {
-			r = -ENOMEM;
-			goto unlock_ret_r;
-		}
+		if (!dd)
+			return -ENOMEM;
 
 		r = dm_get_table_device(t->md, dev, mode, &dd->dm_dev);
 		if (r) {
 			kfree(dd);
-			goto unlock_ret_r;
+			return r;
 		}
 
 		refcount_set(&dd->count, 1);
@@ -403,17 +398,12 @@ int dm_get_device(struct dm_target *ti, const char *path, blk_mode_t mode,
 	} else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
 		r = upgrade_mode(dd, mode, t->md);
 		if (r)
-			goto unlock_ret_r;
+			return r;
 	}
 	refcount_inc(&dd->count);
 out:
-	up_write(&t->devices_lock);
 	*result = dd->dm_dev;
 	return 0;
-
-unlock_ret_r:
-	up_write(&t->devices_lock);
-	return r;
 }
 EXPORT_SYMBOL(dm_get_device);
 
@@ -464,12 +454,9 @@ 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)
 {
 	int found = 0;
-	struct dm_table *t = ti->table;
-	struct list_head *devices = &t->devices;
+	struct list_head *devices = &ti->table->devices;
 	struct dm_dev_internal *dd;
 
-	down_write(&t->devices_lock);
-
 	list_for_each_entry(dd, devices, list) {
 		if (dd->dm_dev == d) {
 			found = 1;
@@ -478,17 +465,14 @@ void dm_put_device(struct dm_target *ti, struct dm_dev *d)
 	}
 	if (!found) {
 		DMERR("%s: device %s not in table devices list",
-		      dm_device_name(t->md), d->name);
-		goto unlock_ret;
+		      dm_device_name(ti->table->md), d->name);
+		return;
 	}
 	if (refcount_dec_and_test(&dd->count)) {
-		dm_put_table_device(t->md, d);
+		dm_put_table_device(ti->table->md, d);
 		list_del(&dd->list);
 		kfree(dd);
 	}
-
-unlock_ret:
-	up_write(&t->devices_lock);
 }
 EXPORT_SYMBOL(dm_put_device);