[PATCH v2 4.19 1/4] ext4: check and update i_disksize properly

[WangYuli <wangyuli@uniontech.com>]

From: Zhang Yi <yi.zhang@huawei.com>

commit 4df031ff5876d94b48dd9ee486ba5522382a06b2 upstream

After commit 3da40c7b0898 ("ext4: only call ext4_truncate when size <=
isize"), i_disksize could always be updated to i_size in ext4_setattr(),
and we could sure that i_disksize <= i_size since holding inode lock and
if i_disksize < i_size there are delalloc writes pending in the range
upto i_size. If the end of the current write is <= i_size, there's no
need to touch i_disksize since writeback will push i_disksize upto
i_size eventually. So we can switch to check i_size instead of
i_disksize in ext4_da_write_end() when write to the end of the file.
we also could remove ext4_mark_inode_dirty() together because we defer
inode dirtying to generic_write_end() or ext4_da_write_inline_data_end().

Cc: stable@vger.kernel.org
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20210716122024.1105856-2-yi.zhang@huawei.com
Reviewed-by: Cheng Nie <niecheng1@uniontech.com>
Signed-off-by: Dandan Zhang <zhangdandan@uniontech.com>
Signed-off-by: WangYuli <wangyuli@uniontech.com>
---
 fs/ext4/inode.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 646285fbc9fc..d8a8e4ee5ff8 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3207,35 +3207,37 @@ static int ext4_da_write_end(struct file *file,
 	end = start + copied - 1;
 
 	/*
-	 * generic_write_end() will run mark_inode_dirty() if i_size
-	 * changes.  So let's piggyback the i_disksize mark_inode_dirty
-	 * into that.
+	 * Since we are holding inode lock, we are sure i_disksize <=
+	 * i_size. We also know that if i_disksize < i_size, there are
+	 * delalloc writes pending in the range upto i_size. If the end of
+	 * the current write is <= i_size, there's no need to touch
+	 * i_disksize since writeback will push i_disksize upto i_size
+	 * eventually. If the end of the current write is > i_size and
+	 * inside an allocated block (ext4_da_should_update_i_disksize()
+	 * check), we need to update i_disksize here as neither
+	 * ext4_writepage() nor certain ext4_writepages() paths not
+	 * allocating blocks update i_disksize.
+	 *
+	 * Note that we defer inode dirtying to generic_write_end() /
+	 * ext4_da_write_inline_data_end().
 	 */
 	new_i_size = pos + copied;
-	if (copied && new_i_size > EXT4_I(inode)->i_disksize) {
+	if (copied && new_i_size > inode->i_size) {
 		if (ext4_has_inline_data(inode) ||
-		    ext4_da_should_update_i_disksize(page, end)) {
+		    ext4_da_should_update_i_disksize(page, end))
 			ext4_update_i_disksize(inode, new_i_size);
-			/* We need to mark inode dirty even if
-			 * new_i_size is less that inode->i_size
-			 * bu greater than i_disksize.(hint delalloc)
-			 */
-			ext4_mark_inode_dirty(handle, inode);
-		}
 	}
 
 	if (write_mode != CONVERT_INLINE_DATA &&
 	    ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) &&
 	    ext4_has_inline_data(inode))
-		ret2 = ext4_da_write_inline_data_end(inode, pos, len, copied,
+		ret = ext4_da_write_inline_data_end(inode, pos, len, copied,
 						     page);
 	else
-		ret2 = generic_write_end(file, mapping, pos, len, copied,
+		ret = generic_write_end(file, mapping, pos, len, copied,
 							page, fsdata);
 
-	copied = ret2;
-	if (ret2 < 0)
-		ret = ret2;
+	copied = ret;
 	ret2 = ext4_journal_stop(handle);
 	if (!ret)
 		ret = ret2;
-- 
2.43.4