[PATCH v4 20/23] ext4: wait for ordered I/O to complete during insert and collapse range

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

Currently, i_disksize is updated after ordered data writeback to prevent
exposing stale data in the post-EOF block, and operations like append
allocate, zero range, and truncate defer the i_disksize update until
ordered I/O completes.

However, insert range and collapse range still directly update
i_disksize. This is safe because they have already called
filemap_write_and_wait_range() to flush data up to LLONG_MAX, ensuring
that ordered I/O has completed if any dirty data was present.

One exception is when the ordered I/O is caused by a previous truncate
up. In this case, there is no dirty data to flush. Therefore, add an
explicit wait for I/O completion to handle this case. This will not have
significant impact on performance.

Finally, also add a WARN_ON_ONCE check before updating i_disksize to
detect any unexpected cases that could still expose stale data.

Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 fs/ext4/extents.c | 18 ++++++++++++++++++
 fs/ext4/inode.c   |  4 +++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 125f628e738a..85c74c37f0ca 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -5565,6 +5565,14 @@ static int ext4_collapse_range(struct file *file, loff_t offset, loff_t len)
 	if (ret)
 		return ret;
 
+	/*
+	 * Wait for ordered I/O to be complete. Updating i_disksize beyond
+	 * the current i_disksize here risks exposuring stale data.
+	 */
+	if (ext4_inode_buffered_iomap(inode))
+		wait_event(EXT4_I(inode)->i_ordered_wq,
+			   READ_ONCE(EXT4_I(inode)->i_ordered_len) == 0);
+
 	truncate_pagecache(inode, start);
 
 	credits = ext4_chunk_trans_extent(inode, 0);
@@ -5597,6 +5605,7 @@ static int ext4_collapse_range(struct file *file, loff_t offset, loff_t len)
 		goto out_handle;
 	}
 
+	WARN_ON_ONCE(READ_ONCE(EXT4_I(inode)->i_ordered_len) != 0);
 	new_size = inode->i_size - len;
 	i_size_write(inode, new_size);
 	EXT4_I(inode)->i_disksize = new_size;
@@ -5661,6 +5670,14 @@ static int ext4_insert_range(struct file *file, loff_t offset, loff_t len)
 	if (ret)
 		return ret;
 
+	/*
+	 * Wait for ordered I/O to be complete. Updating i_disksize beyond
+	 * the current i_disksize here risks exposuring stale data.
+	 */
+	if (ext4_inode_buffered_iomap(inode))
+		wait_event(EXT4_I(inode)->i_ordered_wq,
+			   READ_ONCE(EXT4_I(inode)->i_ordered_len) == 0);
+
 	truncate_pagecache(inode, start);
 
 	credits = ext4_chunk_trans_extent(inode, 0);
@@ -5671,6 +5688,7 @@ static int ext4_insert_range(struct file *file, loff_t offset, loff_t len)
 	ext4_fc_mark_ineligible(sb, EXT4_FC_REASON_FALLOC_RANGE, handle);
 
 	/* Expand file to avoid data loss if there is error while shifting */
+	WARN_ON_ONCE(READ_ONCE(EXT4_I(inode)->i_ordered_len) != 0);
 	inode->i_size += len;
 	EXT4_I(inode)->i_disksize += len;
 	ret = ext4_mark_inode_dirty(handle, inode);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 23efb44f0c27..e47b504e85c9 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4899,7 +4899,9 @@ int ext4_block_zero_eof(struct inode *inode, loff_t from, loff_t end)
 		 *    i_size by the end_io handler once the ongoing I/O
 		 *    completes.
 		 *
-		 *  - TODO: handle insert range and collapse range.
+		 *  - Insert range and collapse range operations:
+		 *    Wait synchronously for the relevant I/O to complete
+		 *    before updating i_disksize.
 		 */
 		} else if (ext4_inode_buffered_iomap(inode)) {
 			err = ext4_iomap_submit_zero_block(inode, from, end);
-- 
2.52.0