ext4: fix COLLAPSE_RANGE failure with 1KB block size

When formatting with 1KB or 2KB(not aligned with PAGE SIZE) block
size, xfstests generic/075 and 091 are failing. The offset supplied to
function truncate_pagecache_range is block size aligned. In this
function start offset is re-aligned to PAGE_SIZE by rounding_up to the
next page boundary.  Due to this rounding up, old data remains in the
page cache when blocksize is less than page size and start offset is
not aligned with page size.  In case of collapse range, we need to
align start offset to page size boundary by doing a round down
operation instead of round up.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/extents.c

@@ -5395,7 +5395,7 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
 	ext4_lblk_t punch_start, punch_stop;
 	handle_t *handle;
 	unsigned int credits;
-	loff_t new_size;
+	loff_t new_size, ioffset;
 	int ret;
 
 	/* Collapse range works only on fs block size aligned offsets. */
@@ -5418,8 +5418,15 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
 			return ret;
 	}
 
+	/*
+	 * Need to round down offset to be aligned with page size boundary
+	 * for page size > block size.
+	 */
+	ioffset = round_down(offset, PAGE_SIZE);
+
 	/* Write out all dirty pages */
-	ret = filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
+	ret = filemap_write_and_wait_range(inode->i_mapping, ioffset,
+					   LLONG_MAX);
 	if (ret)
 		return ret;
 
@@ -5441,7 +5448,7 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
 		goto out_mutex;
 	}
 
-	truncate_pagecache(inode, offset);
+	truncate_pagecache(inode, ioffset);
 
 	/* Wait for existing dio to complete */
 	ext4_inode_block_unlocked_dio(inode);