btrfs: use the correct type to initialize block reserve for delayed refs

When initializing the delayed refs block reserve for a transaction handle
we are passing a type of BTRFS_BLOCK_RSV_DELOPS, which is meant for
delayed items and not for delayed refs. The correct type for delayed refs
is BTRFS_BLOCK_RSV_DELREFS.

On release of any excess space reserved in a local delayed refs reserve,
we also should transfer that excess space to the global block reserve
(it it's full, we return to the space info for general availability).

By initializing a transaction's local delayed refs block reserve with a
type of BTRFS_BLOCK_RSV_DELOPS, we were also causing any excess space
released from the delayed block reserve (fs_info->delayed_block_rsv, used
for delayed inodes and items) to be transferred to the global block
reserve instead of the global delayed refs block reserve. This was an
unintentional change in commit 28270e2 ("btrfs: always reserve space
for delayed refs when starting transaction"), but it's not particularly
serious as things tend to cancel out each other most of the time and it's
relatively rare to be anywhere near exhaustion of the global reserve.

Fix this by initializing a transaction's local delayed refs reserve with
a type of BTRFS_BLOCK_RSV_DELREFS and making btrfs_block_rsv_release()
attempt to transfer unused space from such a reserve into the global block
reserve, just as we did before that commit for when the block reserve is
a delayed refs rsv.

Reported-by: Alex Lyakas <alex.lyakas@zadara.com>
Link: https://lore.kernel.org/linux-btrfs/CAOcd+r0FHG5LWzTSu=LknwSoqxfw+C00gFAW7fuX71+Z5AfEew@mail.gmail.com/
Fixes: 28270e2 ("btrfs: always reserve space for delayed refs when starting transaction")
Reviewed-by: Alex Lyakas <alex.lyakas@zadara.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/block-rsv.c

@@ -276,10 +276,11 @@ u64 btrfs_block_rsv_release(struct btrfs_fs_info *fs_info,
 	struct btrfs_block_rsv *target = NULL;
 
 	/*
-	 * If we are a delayed block reserve then push to the global rsv,
-	 * otherwise dump into the global delayed reserve if it is not full.
+	 * If we are a delayed refs block reserve then push to the global
+	 * reserve, otherwise dump into the global delayed refs reserve if it is
+	 * not full.
 	 */
-	if (block_rsv->type == BTRFS_BLOCK_RSV_DELOPS)
+	if (block_rsv->type == BTRFS_BLOCK_RSV_DELREFS)
 		target = global_rsv;
 	else if (block_rsv != global_rsv && !btrfs_block_rsv_full(delayed_rsv))
 		target = delayed_rsv;

fs/btrfs/transaction.c

@@ -726,7 +726,7 @@ start_transaction(struct btrfs_root *root, unsigned int num_items,
 
 	h->type = type;
 	INIT_LIST_HEAD(&h->new_bgs);
-	btrfs_init_metadata_block_rsv(fs_info, &h->delayed_rsv, BTRFS_BLOCK_RSV_DELOPS);
+	btrfs_init_metadata_block_rsv(fs_info, &h->delayed_rsv, BTRFS_BLOCK_RSV_DELREFS);
 
 	smp_mb();
 	if (cur_trans->state >= TRANS_STATE_COMMIT_START &&