ext4: Fix special handling of journalled data from extent zeroing

The handling of journalled data in ext4_zero_range() is incomplete. We
do not need to commit running transaction but we rather need to
checkpoint pages with journalled data. If we don't, journal tail can be
advanced beyond transaction containing the journalled data and if we
then crash before committing the transaction doing the zeroing we will
have inconsistent (too old) data in the file. Make sure file pages with
journalled data are properly checkpointed before removing them from the
page cache.

Signed-off-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: jankara

fs/ext4/extents.c

@@ -4526,13 +4526,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 
 	trace_ext4_zero_range(inode, offset, len, mode);
 
-	/* Call ext4_force_commit to flush all data in case of data=journal. */
-	if (ext4_should_journal_data(inode)) {
-		ret = ext4_force_commit(inode->i_sb);
-		if (ret)
-			return ret;
-	}
-
 	/*
 	 * Round up offset. This is not fallocate, we need to zero out
 	 * blocks, so convert interior block aligned part of the range to
@@ -4616,6 +4609,20 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 			filemap_invalidate_unlock(mapping);
 			goto out_mutex;
 		}
+
+		/*
+		 * For journalled data we need to write (and checkpoint) pages
+		 * before discarding page cache to avoid inconsitent data on
+		 * disk in case of crash before zeroing trans is committed.
+		 */
+		if (ext4_should_journal_data(inode)) {
+			ret = filemap_write_and_wait_range(mapping, start, end);
+			if (ret) {
+				filemap_invalidate_unlock(mapping);
+				goto out_mutex;
+			}
+		}
+
 		/* Now release the pages and zero block aligned part of pages */
 		truncate_pagecache_range(inode, start, end - 1);
 		inode->i_mtime = inode->i_ctime = current_time(inode);