FAILED: patch "[PATCH] ext4: don't set EXT4_GET_BLOCKS_CONVERT when splitting before" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x feaf2a80e78f89ee8a3464126077ba8683b62791
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026022422-humorous-scam-a54d@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From feaf2a80e78f89ee8a3464126077ba8683b62791 Mon Sep 17 00:00:00 2001
From: Zhang Yi <[email protected]>
Date: Sat, 29 Nov 2025 18:32:35 +0800
Subject: [PATCH] ext4: don't set EXT4_GET_BLOCKS_CONVERT when splitting before
submitting I/O

When allocating blocks during within-EOF DIO and writeback with dioread_nolock enabled, EXT4_GET_BLOCKS_PRE_IO was set to split an existing large unwritten extent. However, EXT4_GET_BLOCKS_CONVERT was set when calling ext4_split_convert_extents(), which may potentially result in stale data issues.

Assume we have an unwritten extent, and then DIO writes the second half.

[UUUUUUUUUUUUUUUU] on-disk extent U: unwritten extent
[UUUUUUUUUUUUUUUU] extent status tree

            |<-   ->| ----> dio write this range

First, ext4_iomap_alloc() call ext4_map_blocks() with EXT4_GET_BLOCKS_PRE_IO, EXT4_GET_BLOCKS_UNWRIT_EXT and EXT4_GET_BLOCKS_CREATE flags set. ext4_map_blocks() find this extent and call ext4_split_convert_extents() with EXT4_GET_BLOCKS_CONVERT and the above flags set.

Then, ext4_split_convert_extents() calls ext4_split_extent() with EXT4_EXT_MAY_ZEROOUT, EXT4_EXT_MARK_UNWRIT2 and EXT4_EXT_DATA_VALID2 flags set, and it calls ext4_split_extent_at() to split the second half with EXT4_EXT_DATA_VALID2, EXT4_EXT_MARK_UNWRIT1, EXT4_EXT_MAY_ZEROOUT and EXT4_EXT_MARK_UNWRIT2 flags set. However, ext4_split_extent_at() failed to insert extent since a temporary lack -ENOSPC. It zeroes out the first half but convert the entire on-disk extent to written since the EXT4_EXT_DATA_VALID2 flag set, but left the second half as unwritten in the extent status tree.

   [0000000000SSSSSS]  data                S: stale data, 0: zeroed
   [WWWWWWWWWWWWWWWW]  on-disk extent      W: written extent
   [WWWWWWWWWWUUUUUU]  extent status tree

Finally, if the DIO failed to write data to the disk, the stale data in the second half will be exposed once the cached extent entry is gone.

Fix this issue by not passing EXT4_GET_BLOCKS_CONVERT when splitting an unwritten extent before submitting I/O, and make ext4_split_convert_extents() to zero out the entire extent range to zero for this case, and also mark the extent in the extent status tree for consistency.

Message-ID: <[email protected]>

index 1fee84ea20af..91b56de60c90 100644
@@ -3746,15 +3746,19 @@ static struct ext4_ext_path *ext4_split_convert_extents(handle_t *handle,
 	/* Convert to unwritten */
 	if (flags & EXT4_GET_BLOCKS_CONVERT_UNWRITTEN) {
 		split_flag |= EXT4_EXT_DATA_ENTIRE_VALID1;
-	/* Convert to initialized */
-	} else if (flags & EXT4_GET_BLOCKS_CONVERT) {
+	/* Split the existing unwritten extent */
+	} else if (flags & (EXT4_GET_BLOCKS_UNWRIT_EXT |
+			    EXT4_GET_BLOCKS_CONVERT)) {
 		/*
 		 * It is safe to convert extent to initialized via explicit
 		 * zeroout only if extent is fully inside i_size or new_size.
 		 */
 		split_flag |= ee_block + ee_len <= eof_block ?
 			      EXT4_EXT_MAY_ZEROOUT : 0;
-		split_flag |= (EXT4_EXT_MARK_UNWRIT2 | EXT4_EXT_DATA_VALID2);
+		split_flag |= EXT4_EXT_MARK_UNWRIT2;
+		/* Convert to initialized */
+		if (flags & EXT4_GET_BLOCKS_CONVERT)
+			split_flag |= EXT4_EXT_DATA_VALID2;
 	}
 	flags |= EXT4_GET_BLOCKS_SPLIT_NOMERGE;
 	return ext4_split_extent(handle, inode, path, map, split_flag, flags,

@@ -3930,7 +3934,7 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
 	/* get_block() before submitting IO, split the extent */
 	if (flags & EXT4_GET_BLOCKS_SPLIT_NOMERGE) {
 		path = ext4_split_convert_extents(handle, inode, map, path,
-				flags | EXT4_GET_BLOCKS_CONVERT, allocated);
+						  flags, allocated);
 		if (IS_ERR(path))
 			return path;
 		/*

From: Zhang Yi <[email protected]>

[ Upstream commit feaf2a80e78f89ee8a3464126077ba8683b62791 ]

When allocating blocks during within-EOF DIO and writeback with dioread_nolock enabled, EXT4_GET_BLOCKS_PRE_IO was set to split an existing large unwritten extent. However, EXT4_GET_BLOCKS_CONVERT was set when calling ext4_split_convert_extents(), which may potentially result in stale data issues.

Assume we have an unwritten extent, and then DIO writes the second half.

[UUUUUUUUUUUUUUUU] on-disk extent U: unwritten extent
[UUUUUUUUUUUUUUUU] extent status tree

            |<-   ->| ----> dio write this range

First, ext4_iomap_alloc() call ext4_map_blocks() with EXT4_GET_BLOCKS_PRE_IO, EXT4_GET_BLOCKS_UNWRIT_EXT and EXT4_GET_BLOCKS_CREATE flags set. ext4_map_blocks() find this extent and call ext4_split_convert_extents() with EXT4_GET_BLOCKS_CONVERT and the above flags set.

Then, ext4_split_convert_extents() calls ext4_split_extent() with EXT4_EXT_MAY_ZEROOUT, EXT4_EXT_MARK_UNWRIT2 and EXT4_EXT_DATA_VALID2 flags set, and it calls ext4_split_extent_at() to split the second half with EXT4_EXT_DATA_VALID2, EXT4_EXT_MARK_UNWRIT1, EXT4_EXT_MAY_ZEROOUT and EXT4_EXT_MARK_UNWRIT2 flags set. However, ext4_split_extent_at() failed to insert extent since a temporary lack -ENOSPC. It zeroes out the first half but convert the entire on-disk extent to written since the EXT4_EXT_DATA_VALID2 flag set, but left the second half as unwritten in the extent status tree.

   [0000000000SSSSSS]  data                S: stale data, 0: zeroed
   [WWWWWWWWWWWWWWWW]  on-disk extent      W: written extent
   [WWWWWWWWWWUUUUUU]  extent status tree

Finally, if the DIO failed to write data to the disk, the stale data in the second half will be exposed once the cached extent entry is gone.

Fix this issue by not passing EXT4_GET_BLOCKS_CONVERT when splitting an unwritten extent before submitting I/O, and make ext4_split_convert_extents() to zero out the entire extent range to zero for this case, and also mark the extent in the extent status tree for consistency.

Message-ID: <[email protected]>

---
 fs/ext4/extents.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

index 1aad4ae0e7ae4..dfc365b021094 100644
@@ -3705,11 +3705,15 @@ static int ext4_split_convert_extents(handle_t *handle,
 	/* Convert to unwritten */
 	if (flags & EXT4_GET_BLOCKS_CONVERT_UNWRITTEN) {
 		split_flag |= EXT4_EXT_DATA_VALID1;
-	/* Convert to initialized */
-	} else if (flags & EXT4_GET_BLOCKS_CONVERT) {
+	/* Split the existing unwritten extent */
+	} else if (flags & (EXT4_GET_BLOCKS_UNWRIT_EXT |
+			    EXT4_GET_BLOCKS_CONVERT)) {
 		split_flag |= ee_block + ee_len <= eof_block ?
 			      EXT4_EXT_MAY_ZEROOUT : 0;
-		split_flag |= (EXT4_EXT_MARK_UNWRIT2 | EXT4_EXT_DATA_VALID2);
+		split_flag |= EXT4_EXT_MARK_UNWRIT2;
+		/* Convert to initialized */
+		if (flags & EXT4_GET_BLOCKS_CONVERT)
+			split_flag |= EXT4_EXT_DATA_VALID2;
 	}
 	flags |= EXT4_GET_BLOCKS_PRE_IO;
 	return ext4_split_extent(handle, inode, ppath, map, split_flag, flags);

@@ -3874,7 +3878,7 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
 	/* get_block() before submitting IO, split the extent */
 	if (flags & EXT4_GET_BLOCKS_PRE_IO) {
 		ret = ext4_split_convert_extents(handle, inode, map, ppath,
-					 flags | EXT4_GET_BLOCKS_CONVERT);
+					 flags);
 		if (ret < 0) {
 			err = ret;
 			goto out2;

2.51.0

Does not apply :(