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, 12 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 73de042158f1..4fc6acf65220 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3003,6 +3003,16 @@ static int btrfs_relocate_chunk(struct btrfs_fs_info *fs_info, u64 chunk_offset)
 	if (ret)
 		return ret;
 
+	/*
+	 * We add the kobjects here (and after forcing data chunk creation)
+	 * since relocation is the only place we'll create chunks of a new
+	 * type at runtime.  The only place where we'll remove the last
+	 * chunk of a type is the call immediately below this one.  Even
+	 * so, we're protected against races with the cleaner thread since
+	 * we're covered by the delete_unused_bgs_mutex.
+	 */
+	btrfs_add_raid_kobjects(fs_info);
+
 	trans = btrfs_start_trans_remove_block_group(root->fs_info,
 						     chunk_offset);
 	if (IS_ERR(trans)) {
@@ -3130,6 +3140,8 @@ static int btrfs_may_alloc_data_chunk(struct btrfs_fs_info *fs_info,
 			if (ret < 0)
 				return ret;
 
+			btrfs_add_raid_kobjects(fs_info);
+
 			return 1;
 		}
 	}