Btrfs: do transaction space reservation before joining the transaction

We have to do weird things when handling enospc in the transaction joining code.
Because we've already joined the transaction we cannot commit the transaction
within the reservation code since it will deadlock, so we have to return EAGAIN
and then make sure we don't retry too many times.  Instead of doing this, just
do the reservation the normal way before we join the transaction, that way we
can do whatever we want to try and reclaim space, and then if it fails we know
for sure we are out of space and we can return ENOSPC.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 17 insertions, 19 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 51dcec86757..654755b1895 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -260,7 +260,7 @@ static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
 {
         struct btrfs_trans_handle *h;
         struct btrfs_transaction *cur_trans;
-        int retries = 0;
+        u64 num_bytes = 0;
         int ret;
 
         if (root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR)
@@ -274,6 +274,19 @@ static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
                 h->block_rsv = NULL;
                 goto got_it;
         }
+
+        /*
+         * Do the reservation before we join the transaction so we can do all
+         * the appropriate flushing if need be.
+         */
+        if (num_items > 0 && root != root->fs_info->chunk_root) {
+                num_bytes = btrfs_calc_trans_metadata_size(root, num_items);
+                ret = btrfs_block_rsv_add(NULL, root,
+                                          &root->fs_info->trans_block_rsv,
+                                          num_bytes);
+                if (ret)
+                        return ERR_PTR(ret);
+        }
 again:
         h = kmem_cache_alloc(btrfs_trans_handle_cachep, GFP_NOFS);
         if (!h)
@@ -310,24 +323,9 @@ again:
                 goto again;
         }
 
-        if (num_items > 0) {
-                ret = btrfs_trans_reserve_metadata(h, root, num_items);
-                if (ret == -EAGAIN && !retries) {
-                        retries++;
-                        btrfs_commit_transaction(h, root);
-                        goto again;
-                } else if (ret == -EAGAIN) {
-                        /*
-                         * We have already retried and got EAGAIN, so really we
-                         * don't have space, so set ret to -ENOSPC.
-                         */
-                        ret = -ENOSPC;
-                }
-
-                if (ret < 0) {
-                        btrfs_end_transaction(h, root);
-                        return ERR_PTR(ret);
-                }
+        if (num_bytes) {
+                h->block_rsv = &root->fs_info->trans_block_rsv;
+                h->bytes_reserved = num_bytes;
         }
 
 got_it: