Btrfs: fix enospc problems with delalloc

So I had this brilliant idea to use atomic counters for outstanding and reserved
extents, but this turned out to be a bad idea.  Consider this where we have 1
outstanding extent and 1 reserved extent

Reserver				Releaser
					atomic_dec(outstanding) now 0
atomic_read(outstanding)+1 get 1
atomic_read(reserved) get 1
don't actually reserve anything because
they are the same
					atomic_cmpxchg(reserved, 1, 0)
atomic_inc(outstanding)
atomic_add(0, reserved)
					free reserved space for 1 extent

Then the reserver now has no actual space reserved for it, and when it goes to
finish the ordered IO it won't have enough space to do it's allocation and you
get those lovely warnings.

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 52d7eca8c7bf..03dce3f40ce0 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -34,6 +34,9 @@ struct btrfs_inode {
          */
         struct btrfs_key location;
 
+        /* Lock for counters */
+        spinlock_t lock;
+
         /* the extent_tree has caches of all the extent mappings to disk */
         struct extent_map_tree extent_tree;
 
@@ -134,8 +137,8 @@ struct btrfs_inode {
          * items we think we'll end up using, and reserved_extents is the number
          * of extent items we've reserved metadata for.
          */
-        atomic_t outstanding_extents;
-        atomic_t reserved_extents;
+        unsigned outstanding_extents;
+        unsigned reserved_extents;
 
         /*
          * ordered_data_close is set by truncate when a file that used