patches/old/fs-ext4-transition-from-deprecated-mmap-hook-to-mmap_prepare.patch

From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Subject: fs/ext4: transition from deprecated .mmap hook to .mmap_prepare
Date: Mon, 16 Jun 2025 20:33:24 +0100

Since commit c84bf6dd2b83 ("mm: introduce new .mmap_prepare() file
callback"), the f_op->mmap() hook has been deprecated in favour of
f_op->mmap_prepare().

This callback is invoked in the mmap() logic far earlier, so error
handling can be performed more safely without complicated and bug-prone
state unwinding required should an error arise.

This hook also avoids passing a pointer to a not-yet-correctly-established
VMA avoiding any issues with referencing this data structure.

It rather provides a pointer to the new struct vm_area_desc descriptor
type which contains all required state and allows easy setting of required
parameters without any consideration needing to be paid to locking or
reference counts.

Note that nested filesystems like overlayfs are compatible with an
.mmap_prepare() callback since commit bb666b7c2707 ("mm: add
mmap_prepare() compatibility layer for nested file systems").

Link: https://lkml.kernel.org/r/5abfe526032a6698fd1bcd074a74165cda7ea57c.1750099179.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/ext4/file.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

--- a/fs/ext4/file.c~fs-ext4-transition-from-deprecated-mmap-hook-to-mmap_prepare
+++ a/fs/ext4/file.c
@@ -804,9 +804,10 @@ static const struct vm_operations_struct
 	.page_mkwrite   = ext4_page_mkwrite,
 };
 
-static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
+static int ext4_file_mmap_prepare(struct vm_area_desc *desc)
 {
 	int ret;
+	struct file *file = desc->file;
 	struct inode *inode = file->f_mapping->host;
 	struct dax_device *dax_dev = EXT4_SB(inode->i_sb)->s_daxdev;
 
@@ -821,15 +822,15 @@ static int ext4_file_mmap(struct file *f
 	 * We don't support synchronous mappings for non-DAX files and
 	 * for DAX files if underneath dax_device is not synchronous.
 	 */
-	if (!daxdev_mapping_supported(vma->vm_flags, vma->vm_file, dax_dev))
+	if (!daxdev_mapping_supported(desc->vm_flags, file, dax_dev))
 		return -EOPNOTSUPP;
 
 	file_accessed(file);
 	if (IS_DAX(file_inode(file))) {
-		vma->vm_ops = &ext4_dax_vm_ops;
-		vm_flags_set(vma, VM_HUGEPAGE);
+		desc->vm_ops = &ext4_dax_vm_ops;
+		desc->vm_flags |= VM_HUGEPAGE;
 	} else {
-		vma->vm_ops = &ext4_file_vm_ops;
+		desc->vm_ops = &ext4_file_vm_ops;
 	}
 	return 0;
 }
@@ -968,7 +969,7 @@ const struct file_operations ext4_file_o
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= ext4_compat_ioctl,
 #endif
-	.mmap		= ext4_file_mmap,
+	.mmap_prepare	= ext4_file_mmap_prepare,
 	.open		= ext4_file_open,
 	.release	= ext4_release_file,
 	.fsync		= ext4_sync_file,
_