1 files changed, 19 insertions, 2 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index faff98f720de..e035731b3608 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3672,13 +3672,30 @@ static int can_overcommit(struct btrfs_root *root,
                           struct btrfs_space_info *space_info, u64 bytes,
                           enum btrfs_reserve_flush_enum flush)
 {
+        struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
         u64 profile = btrfs_get_alloc_profile(root, 0);
+        u64 rsv_size = 0;
         u64 avail;
         u64 used;
 
         used = space_info->bytes_used + space_info->bytes_reserved +
-                space_info->bytes_pinned + space_info->bytes_readonly +
-                space_info->bytes_may_use;
+                space_info->bytes_pinned + space_info->bytes_readonly;
+
+        spin_lock(&global_rsv->lock);
+        rsv_size = global_rsv->size;
+        spin_unlock(&global_rsv->lock);
+
+        /*
+         * We only want to allow over committing if we have lots of actual space
+         * free, but if we don't have enough space to handle the global reserve
+         * space then we could end up having a real enospc problem when trying
+         * to allocate a chunk or some other such important allocation.
+         */
+        rsv_size <<= 1;
+        if (used + rsv_size >= space_info->total_bytes)
+                return 0;
+
+        used += space_info->bytes_may_use;
 
         spin_lock(&root->fs_info->free_chunk_lock);
         avail = root->fs_info->free_chunk_space;