Friendpaste

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index b077544b5232..e742965e4bc3 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -777,16 +777,21 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
                goto free_pending;
        }
 
+       /*
+        * Flush dealloc writes before incrementing root->will_be_snapshotted to
+        * avoid as many nocow writes as possible to fallback to COW mode (which
+        * could run into ENOSPC).
+        */
+       ret = btrfs_start_delalloc_inodes(root);
+       if (ret)
+               goto dec_and_free;
+
        atomic_inc(&root->will_be_snapshotted);
        smp_mb__after_atomic();
        /* wait for no snapshot writes */
        wait_event(root->subv_writers->wait,
                   percpu_counter_sum(&root->subv_writers->counter) == 0);
 
-       ret = btrfs_start_delalloc_inodes(root);
-       if (ret)
-               goto dec_and_free;
-
        btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
 
        btrfs_init_block_rsv(&pending_snapshot->block_rsv,