FAILED: patch "[PATCH] iomap: reject delalloc mappings during writeback" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x d320f160aa5ff36cdf83c645cca52b615e866e32
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026031714-renderer-twiddling-44fe@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From d320f160aa5ff36cdf83c645cca52b615e866e32 Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <[email protected]>
Date: Mon, 2 Mar 2026 09:30:02 -0800
Subject: [PATCH] iomap: reject delalloc mappings during writeback

Filesystems should never provide a delayed allocation mapping to writeback; they're supposed to allocate the space before replying. This can lead to weird IO errors and crashes in the block layer if the filesystem is being malicious, or if it hadn't set iomap->dev because it's a delalloc mapping.

Fix this by failing writeback on delalloc mappings. Currently no filesystems actually misbehave in this manner, but we ought to be stricter about things like that.

index 4d1ef8a2cee9..60546fa14dfe 100644
@@ -215,17 +215,18 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
 	WARN_ON_ONCE(!folio->private && map_len < dirty_len);
 
 	switch (wpc->iomap.type) {
-	case IOMAP_INLINE:
-		WARN_ON_ONCE(1);
-		return -EIO;
+	case IOMAP_UNWRITTEN:
+		ioend_flags |= IOMAP_IOEND_UNWRITTEN;
+		break;
+	case IOMAP_MAPPED:
+		break;
 	case IOMAP_HOLE:
 		return map_len;
 	default:
-		break;
+		WARN_ON_ONCE(1);
+		return -EIO;
 	}
 
-	if (wpc->iomap.type == IOMAP_UNWRITTEN)
-		ioend_flags |= IOMAP_IOEND_UNWRITTEN;
 	if (wpc->iomap.flags & IOMAP_F_SHARED)
 		ioend_flags |= IOMAP_IOEND_SHARED;
 	if (folio_test_dropbehind(folio))

From: "Darrick J. Wong" <[email protected]>

[ Upstream commit d320f160aa5ff36cdf83c645cca52b615e866e32 ]

Filesystems should never provide a delayed allocation mapping to writeback; they're supposed to allocate the space before replying. This can lead to weird IO errors and crashes in the block layer if the filesystem is being malicious, or if it hadn't set iomap->dev because it's a delalloc mapping.

Fix this by failing writeback on delalloc mappings. Currently no filesystems actually misbehave in this manner, but we ought to be stricter about things like that.

---
 fs/iomap/buffered-io.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

index 87a4f5a2ded0e..ee22d4ff74a95 100644
@@ -1320,10 +1320,13 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 		error = wpc->ops->map_blocks(wpc, inode, file_offset);
 		if (error)
 			break;
-		if (WARN_ON_ONCE(wpc->iomap.type == IOMAP_INLINE))
-			continue;
 		if (wpc->iomap.type == IOMAP_HOLE)
 			continue;
+		if (WARN_ON_ONCE(wpc->iomap.type != IOMAP_UNWRITTEN &&
+				 wpc->iomap.type != IOMAP_MAPPED)) {
+			error = -EIO;
+			break;
+		}
 		iomap_add_to_ioend(inode, file_offset, page, iop, wpc, wbc,
 				 &submit_list);
 		count++;

2.51.0