[PATCH] btrfs: allocate raid type kobjects dynamically

[Jeff Mahoney <jeffm@suse.com>]

We are currently allocating space_info objects in an array when we
allocate space_info. When a user does something like:

# btrfs balance start -mconvert=raid1 -dconvert=raid1 /mnt
# btrfs balance start -mconvert=single -dconvert=single /mnt -f
# btrfs balance start -mconvert=raid1 -dconvert=raid1 /

We can end up with memory corruption since the kobject hasn't
been reinitialized properly and the name pointer was left set.

The rationale behind allocating them statically was to avoid
creating a separate kobject container that just contained the
raid type. It used the index in the array to determine the index.

Ultimately, though, this wastes more memory than it saves in all
but the most complex scenarios and introduces kobject lifetime
questions.

This patch allocates the kobjects dynamically instead. Note that
we also remove the kobject_get/put of the parent kobject since
kobject_add and kobject_del do that internally.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---
 fs/btrfs/ctree.h       |    8 +++++++-
 fs/btrfs/extent-tree.c |   33 +++++++++++++++++++++------------
 fs/btrfs/sysfs.c       |    5 +++--
 3 files changed, 31 insertions(+), 15 deletions(-)

--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1113,6 +1113,12 @@ struct btrfs_qgroup_limit_item {
 	__le64 rsv_excl;
 } __attribute__ ((__packed__));
 
+/* For raid type sysfs entries */
+struct raid_kobject {
+	int raid_type;
+	struct kobject kobj;
+};
+
 struct btrfs_space_info {
 	spinlock_t lock;
 
@@ -1163,7 +1169,7 @@ struct btrfs_space_info {
 	wait_queue_head_t wait;
 
 	struct kobject kobj;
-	struct kobject block_group_kobjs[BTRFS_NR_RAID_TYPES];
+	struct kobject *block_group_kobjs[BTRFS_NR_RAID_TYPES];
 };
 
 #define	BTRFS_BLOCK_RSV_GLOBAL		1
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3401,10 +3401,8 @@ static int update_space_info(struct btrf
 		return ret;
 	}
 
-	for (i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
+	for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
 		INIT_LIST_HEAD(&found->block_groups[i]);
-		kobject_init(&found->block_group_kobjs[i], &btrfs_raid_ktype);
-	}
 	init_rwsem(&found->groups_sem);
 	spin_lock_init(&found->lock);
 	found->flags = flags & BTRFS_BLOCK_GROUP_TYPE_MASK;
@@ -8327,7 +8325,8 @@ int btrfs_free_block_groups(struct btrfs
 		list_del(&space_info->list);
 		for (i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
 			struct kobject *kobj;
-			kobj = &space_info->block_group_kobjs[i];
+			kobj = space_info->block_group_kobjs[i];
+			space_info->block_group_kobjs[i] = NULL;
 			if (kobj->parent) {
 				kobject_del(kobj);
 				kobject_put(kobj);
@@ -8352,17 +8351,26 @@ static void __link_block_group(struct bt
 	up_write(&space_info->groups_sem);
 
 	if (first) {
-		struct kobject *kobj = &space_info->block_group_kobjs[index];
+		struct raid_kobject *rkobj;
 		int ret;
 
-		kobject_get(&space_info->kobj); /* put in release */
-		ret = kobject_add(kobj, &space_info->kobj, "%s",
-				  get_raid_name(index));
+		rkobj = kzalloc(sizeof(*rkobj), GFP_KERNEL);
+		if (!rkobj)
+			goto out_err;
+		rkobj->raid_type = index;
+		kobject_init(&rkobj->kobj, &btrfs_raid_ktype);
+		ret = kobject_add(&rkobj->kobj, &space_info->kobj,
+				  "%s", get_raid_name(index));
 		if (ret) {
-			pr_warn("BTRFS: failed to add kobject for block cache. ignoring.\n");
-			kobject_put(&space_info->kobj);
+			kobject_put(&rkobj->kobj);
+			goto out_err;
 		}
+		space_info->block_group_kobjs[index] = &rkobj->kobj;
 	}
+
+	return;
+out_err:
+	pr_warn("BTRFS: failed to add kobject for block cache. ignoring.\n");
 }
 
 static struct btrfs_block_group_cache *
@@ -8796,8 +8804,9 @@ int btrfs_remove_block_group(struct btrf
 	 */
 	list_del_init(&block_group->list);
 	if (list_empty(&block_group->space_info->block_groups[index])) {
-		kobject_del(&block_group->space_info->block_group_kobjs[index]);
-		kobject_put(&block_group->space_info->block_group_kobjs[index]);
+		kobject_del(block_group->space_info->block_group_kobjs[index]);
+		kobject_put(block_group->space_info->block_group_kobjs[index]);
+		block_group->space_info->block_group_kobjs[index] = NULL;
 		clear_avail_alloc_bits(root->fs_info, block_group->flags);
 	}
 	up_write(&block_group->space_info->groups_sem);
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -254,6 +254,7 @@ static ssize_t global_rsv_reserved_show(
 BTRFS_ATTR(global_rsv_reserved, 0444, global_rsv_reserved_show);
 
 #define to_space_info(_kobj) container_of(_kobj, struct btrfs_space_info, kobj)
+#define to_raid_kobj(_kobj) container_of(_kobj, struct raid_kobject, kobj)
 
 static ssize_t raid_bytes_show(struct kobject *kobj,
 			       struct kobj_attribute *attr, char *buf);
@@ -266,7 +267,7 @@ static ssize_t raid_bytes_show(struct ko
 {
 	struct btrfs_space_info *sinfo = to_space_info(kobj->parent);
 	struct btrfs_block_group_cache *block_group;
-	int index = kobj - sinfo->block_group_kobjs;
+	int index = to_raid_kobj(kobj)->raid_type;
 	u64 val = 0;
 
 	down_read(&sinfo->groups_sem);
@@ -288,7 +289,7 @@ static struct attribute *raid_attributes
 
 static void release_raid_kobj(struct kobject *kobj)
 {
-	kobject_put(kobj->parent);
+	kfree(to_raid_kobj(kobj));
 }
 
 struct kobj_type btrfs_raid_ktype = {


-- 
Jeff Mahoney
SUSE Labs