ext4: ensure zeroed partial blocks are persisted in SYNC mode

In ext4_zero_range() and ext4_punch_hole(), when operating in SYNC mode
and zeroing a partial block, only data=journal modes guarantee that the
zeroed data is synchronously persisted after the operation completes.
For data=ordered/writeback mode and non-journal modes, this guarantee is
missing.

Introduce a partial_zero parameter to explicitly trigger writeback for
all scenarios where a partial block is zeroed, ensuring the zeroed data
is durably persisted.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20260327102939.1095257-10-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: zhangyi089

fs/ext4/ext4.h

@@ -3099,7 +3099,7 @@ extern int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
 				  int pextents);
 extern int ext4_block_zero_eof(struct inode *inode, loff_t from, loff_t end);
 extern int ext4_zero_partial_blocks(struct inode *inode, loff_t lstart,
-				    loff_t length);
+				    loff_t length, bool *did_zero);
 extern vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf);
 extern qsize_t *ext4_get_reserved_space(struct inode *inode);
 extern int ext4_get_projid(struct inode *inode, kprojid_t *projid);

fs/ext4/extents.c

@@ -4702,6 +4702,7 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 	loff_t align_start, align_end, new_size = 0;
 	loff_t end = offset + len;
 	unsigned int blocksize = i_blocksize(inode);
+	bool partial_zeroed = false;
 	int ret, flags;
 
 	trace_ext4_zero_range(inode, offset, len, mode);
@@ -4757,9 +4758,15 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 		return ret;
 
 	/* Zero out partial block at the edges of the range */
-	ret = ext4_zero_partial_blocks(inode, offset, len);
+	ret = ext4_zero_partial_blocks(inode, offset, len, &partial_zeroed);
 	if (ret)
 		return ret;
+	if (((file->f_flags & O_SYNC) || IS_SYNC(inode)) && partial_zeroed) {
+		ret = filemap_write_and_wait_range(inode->i_mapping, offset,
+						   end - 1);
+		if (ret)
+			return ret;
+	}
 
 	handle = ext4_journal_start(inode, EXT4_HT_MISC, 1);
 	if (IS_ERR(handle)) {

fs/ext4/inode.c

@@ -4257,7 +4257,8 @@ int ext4_block_zero_eof(struct inode *inode, loff_t from, loff_t end)
 	return 0;
 }
 
-int ext4_zero_partial_blocks(struct inode *inode, loff_t lstart, loff_t length)
+int ext4_zero_partial_blocks(struct inode *inode, loff_t lstart, loff_t length,
+			     bool *did_zero)
 {
 	struct super_block *sb = inode->i_sb;
 	unsigned partial_start, partial_end;
@@ -4274,20 +4275,21 @@ int ext4_zero_partial_blocks(struct inode *inode, loff_t lstart, loff_t length)
 	/* Handle partial zero within the single block */
 	if (start == end &&
 	    (partial_start || (partial_end != sb->s_blocksize - 1))) {
-		err = ext4_block_zero_range(inode, lstart, length, NULL, NULL);
+		err = ext4_block_zero_range(inode, lstart, length, did_zero,
+					    NULL);
 		return err;
 	}
 	/* Handle partial zero out on the start of the range */
 	if (partial_start) {
 		err = ext4_block_zero_range(inode, lstart, sb->s_blocksize,
-					    NULL, NULL);
+					    did_zero, NULL);
 		if (err)
 			return err;
 	}
 	/* Handle partial zero out on the end of the range */
 	if (partial_end != sb->s_blocksize - 1)
 		err = ext4_block_zero_range(inode, byte_end - partial_end,
-					    partial_end + 1, NULL, NULL);
+					    partial_end + 1, did_zero, NULL);
 	return err;
 }
 
@@ -4436,6 +4438,7 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
 	loff_t end = offset + length;
 	handle_t *handle;
 	unsigned int credits;
+	bool partial_zeroed = false;
 	int ret;
 
 	trace_ext4_punch_hole(inode, offset, length, 0);
@@ -4471,9 +4474,15 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
 	if (ret)
 		return ret;
 
-	ret = ext4_zero_partial_blocks(inode, offset, length);
+	ret = ext4_zero_partial_blocks(inode, offset, length, &partial_zeroed);
 	if (ret)
 		return ret;
+	if (((file->f_flags & O_SYNC) || IS_SYNC(inode)) && partial_zeroed) {
+		ret = filemap_write_and_wait_range(inode->i_mapping, offset,
+						   end - 1);
+		if (ret)
+			return ret;
+	}
 
 	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
 		credits = ext4_chunk_trans_extent(inode, 0);