Btrfs: fix reservations in btrfs_page_mkwrite

Josef fixed btrfs_page_mkwrite to properly release reserved
extents if there was an error.  But if we fail to get a reservation
and we fail to dirty the inode (for ENOSPC reasons), we'll end up
trying to release a reservation we never had.

This makes sure we only release if we were able to reserve.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 5977987abdb..7405753ec5d 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6401,18 +6401,23 @@ int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
         unsigned long zero_start;
         loff_t size;
         int ret;
+        int reserved = 0;
         u64 page_start;
         u64 page_end;
 
         ret  = btrfs_delalloc_reserve_space(inode, PAGE_CACHE_SIZE);
-        if (!ret)
+        if (!ret) {
                 ret = btrfs_update_time(vma->vm_file);
+                reserved = 1;
+        }
         if (ret) {
                 if (ret == -ENOMEM)
                         ret = VM_FAULT_OOM;
                 else /* -ENOSPC, -EIO, etc */
                         ret = VM_FAULT_SIGBUS;
-                goto out;
+                if (reserved)
+                        goto out;
+                goto out_noreserve;
         }
 
         ret = VM_FAULT_NOPAGE; /* make the VM retry the fault */
@@ -6495,6 +6500,7 @@ out_unlock:
         unlock_page(page);
 out:
         btrfs_delalloc_release_space(inode, PAGE_CACHE_SIZE);
+out_noreserve:
         return ret;
 }