btrfs: Fix a data space underflow warning

Even with quota disabled, generic/127 will trigger a kernel warning by
underflow data space info.

The bug is caused by buffered write, which in case of short copy, the
start parameter for btrfs_delalloc_release_space() is wrong, and
round_up/down() in btrfs_delalloc_release() extents the range to page
aligned, decreasing one more page than expected.

This patch will fix it by passing correct start.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 381be79..e6df6f1 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1604,12 +1604,17 @@ again:
                                BTRFS_I(inode)->outstanding_extents++;
                                spin_unlock(&BTRFS_I(inode)->lock);
                        }
-                       if (only_release_metadata)
+                       if (only_release_metadata) {
                                btrfs_delalloc_release_metadata(inode,
                                                                release_bytes);
-                       else
-                               btrfs_delalloc_release_space(inode, pos,
+                       } else {
+                               u64 __pos;
+
+                               __pos = round_down(pos, root->sectorsize) +
+                                       (dirty_pages << PAGE_CACHE_SHIFT);
+                               btrfs_delalloc_release_space(inode, __pos,
                                                             release_bytes);
+                       }
                }
 
                release_bytes = dirty_pages << PAGE_CACHE_SHIFT;