ext4: fix loss of delalloc extent info in ext4_zero_range()

In ext4_zero_range(), removing a file's entire block range from the
extent status tree removes all records of that file's delalloc extents.
The delalloc accounting code uses this information, and its loss can
then lead to accounting errors and kernel warnings at writeback time and
subsequent file system damage.  This is most noticeable on bigalloc
file systems where code in ext4_ext_map_blocks() handles cases where
delalloc extents share clusters with a newly allocated extent.

Because we're not deleting a block range and are correctly updating the
status of its associated extent, there is no need to remove anything
from the extent status tree.

When this patch is combined with an unrelated bug fix for
ext4_zero_range(), kernel warnings and e2fsck errors reported during
xfstests runs on bigalloc filesystems are greatly reduced without
introducing regressions on other xfstests-bld test scenarios.

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/extents.c

@@ -4848,19 +4848,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 					     flags, mode);
 		if (ret)
 			goto out_dio;
-		/*
-		 * Remove entire range from the extent status tree.
-		 *
-		 * ext4_es_remove_extent(inode, lblk, max_blocks) is
-		 * NOT sufficient.  I'm not sure why this is the case,
-		 * but let's be conservative and remove the extent
-		 * status tree for the entire inode.  There should be
-		 * no outstanding delalloc extents thanks to the
-		 * filemap_write_and_wait_range() call above.
-		 */
-		ret = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
-		if (ret)
-			goto out_dio;
 	}
 	if (!partial_begin && !partial_end)
 		goto out_dio;