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, 23 insertions, 12 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2bf4d2b97d54..55d68ea1866b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1298,7 +1298,9 @@ static int btrfs_split_extent_hook(struct inode *inode,
         if (!(orig->state & EXTENT_DELALLOC))
                 return 0;
 
-        atomic_inc(&BTRFS_I(inode)->outstanding_extents);
+        spin_lock(&BTRFS_I(inode)->lock);
+        BTRFS_I(inode)->outstanding_extents++;
+        spin_unlock(&BTRFS_I(inode)->lock);
         return 0;
 }
 
@@ -1316,7 +1318,9 @@ static int btrfs_merge_extent_hook(struct inode *inode,
         if (!(other->state & EXTENT_DELALLOC))
                 return 0;
 
-        atomic_dec(&BTRFS_I(inode)->outstanding_extents);
+        spin_lock(&BTRFS_I(inode)->lock);
+        BTRFS_I(inode)->outstanding_extents--;
+        spin_unlock(&BTRFS_I(inode)->lock);
         return 0;
 }
 
@@ -1339,10 +1343,13 @@ static int btrfs_set_bit_hook(struct inode *inode,
                 u64 len = state->end + 1 - state->start;
                 bool do_list = !is_free_space_inode(root, inode);
 
-                if (*bits & EXTENT_FIRST_DELALLOC)
+                if (*bits & EXTENT_FIRST_DELALLOC) {
                         *bits &= ~EXTENT_FIRST_DELALLOC;
-                else
-                        atomic_inc(&BTRFS_I(inode)->outstanding_extents);
+                } else {
+                        spin_lock(&BTRFS_I(inode)->lock);
+                        BTRFS_I(inode)->outstanding_extents++;
+                        spin_unlock(&BTRFS_I(inode)->lock);
+                }
 
                 spin_lock(&root->fs_info->delalloc_lock);
                 BTRFS_I(inode)->delalloc_bytes += len;
@@ -1372,10 +1379,13 @@ static int btrfs_clear_bit_hook(struct inode *inode,
                 u64 len = state->end + 1 - state->start;
                 bool do_list = !is_free_space_inode(root, inode);
 
-                if (*bits & EXTENT_FIRST_DELALLOC)
+                if (*bits & EXTENT_FIRST_DELALLOC) {
                         *bits &= ~EXTENT_FIRST_DELALLOC;
-                else if (!(*bits & EXTENT_DO_ACCOUNTING))
-                        atomic_dec(&BTRFS_I(inode)->outstanding_extents);
+                } else if (!(*bits & EXTENT_DO_ACCOUNTING)) {
+                        spin_lock(&BTRFS_I(inode)->lock);
+                        BTRFS_I(inode)->outstanding_extents--;
+                        spin_unlock(&BTRFS_I(inode)->lock);
+                }
 
                 if (*bits & EXTENT_DO_ACCOUNTING)
                         btrfs_delalloc_release_metadata(inode, len);
@@ -6735,8 +6745,9 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
         ei->index_cnt = (u64)-1;
         ei->last_unlink_trans = 0;
 
-        atomic_set(&ei->outstanding_extents, 0);
-        atomic_set(&ei->reserved_extents, 0);
+        spin_lock_init(&ei->lock);
+        ei->outstanding_extents = 0;
+        ei->reserved_extents = 0;
 
         ei->ordered_data_close = 0;
         ei->orphan_meta_reserved = 0;
@@ -6774,8 +6785,8 @@ void btrfs_destroy_inode(struct inode *inode)
 
         WARN_ON(!list_empty(&inode->i_dentry));
         WARN_ON(inode->i_data.nrpages);
-        WARN_ON(atomic_read(&BTRFS_I(inode)->outstanding_extents));
-        WARN_ON(atomic_read(&BTRFS_I(inode)->reserved_extents));
+        WARN_ON(BTRFS_I(inode)->outstanding_extents);
+        WARN_ON(BTRFS_I(inode)->reserved_extents);
 
         /*
          * This can happen where we create an inode, but somebody else also