btrfs: defer adding raid type kobject until after chunk relocation

Any time the first block group of a new type is created, we add a new
kobject to sysfs to hold the attributes for that type.  Kobject-internal
allocations always use GFP_KERNEL, making them prone to fs-reclaim races.
While it appears as if this can occur any time a block group is created,
the only times the first block group of a new type can be created in
memory is at mount and when we create the first new block group during
raid conversion.

This patch adds a new list to track pending kobject additions and then
handles them after we do chunk relocation.  Between relocating the
target chunk (or forcing allocation of a new chunk in the case of data)
and removing the old chunk, we're in a safe place for fs-reclaim to
occur.  We're holding the volume mutex, which is already held across
page faults, and the delete_unused_bgs_mutex, which will only stall
the cleaner thread.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index ffa72ca5755d..8d3aa56b928b 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -385,8 +385,9 @@ struct btrfs_dev_replace {
 
 /* For raid type sysfs entries */
 struct raid_kobject {
-	int raid_type;
+	u64 flags;
 	struct kobject kobj;
+	struct list_head list;
 };
 
 struct btrfs_space_info {
@@ -940,6 +941,8 @@ struct btrfs_fs_info {
 	u32 thread_pool_size;
 
 	struct kobject *space_info_kobj;
+	struct list_head pending_raid_kobjs;
+	spinlock_t pending_raid_kobjs_lock; /* uncontended */
 
 	u64 total_pinned;
 
@@ -2700,6 +2703,7 @@ int btrfs_can_relocate(struct btrfs_fs_info *fs_info, u64 bytenr);
 int btrfs_make_block_group(struct btrfs_trans_handle *trans,
 			   struct btrfs_fs_info *fs_info, u64 bytes_used,
 			   u64 type, u64 chunk_offset, u64 size);
+void btrfs_add_raid_kobjects(struct btrfs_fs_info *fs_info);
 struct btrfs_trans_handle *btrfs_start_trans_remove_block_group(
 				struct btrfs_fs_info *fs_info,
 				const u64 chunk_offset);