[PATCH v4 1/3] kernfs: remove page_mkwrite() from vm_operations_struct

[Martin Oliveira <martin.oliveira@xxxxxxxxxxxxx>]

The .page_mkwrite operator of kernfs just calls file_update_time().
This is the same behaviour that the fault code does if .page_mkwrite is
not set.

Furthermore, having the page_mkwrite() operator causes
writable_file_mapping_allowed() to fail due to
vma_needs_dirty_tracking() on the gup flow, which is a pre-requisite for
enabling P2PDMA over RDMA.

There are no users of .page_mkwrite and no known valid use cases, so
just remove the .page_mkwrite from kernfs_ops and WARN if an mmap()
implementation sets .page_mkwrite.

Co-developed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Signed-off-by: Martin Oliveira <martin.oliveira@xxxxxxxxxxxxx>
---
 fs/kernfs/file.c | 40 +++++++++++-----------------------------
 1 file changed, 11 insertions(+), 29 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 8502ef68459b..fb2b77bf0c04 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -386,28 +386,6 @@ static vm_fault_t kernfs_vma_fault(struct vm_fault *vmf)
 	return ret;
 }
 
-static vm_fault_t kernfs_vma_page_mkwrite(struct vm_fault *vmf)
-{
-	struct file *file = vmf->vma->vm_file;
-	struct kernfs_open_file *of = kernfs_of(file);
-	vm_fault_t ret;
-
-	if (!of->vm_ops)
-		return VM_FAULT_SIGBUS;
-
-	if (!kernfs_get_active(of->kn))
-		return VM_FAULT_SIGBUS;
-
-	ret = 0;
-	if (of->vm_ops->page_mkwrite)
-		ret = of->vm_ops->page_mkwrite(vmf);
-	else
-		file_update_time(file);
-
-	kernfs_put_active(of->kn);
-	return ret;
-}
-
 static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr,
 			     void *buf, int len, int write)
 {
@@ -432,7 +410,6 @@ static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr,
 static const struct vm_operations_struct kernfs_vm_ops = {
 	.open		= kernfs_vma_open,
 	.fault		= kernfs_vma_fault,
-	.page_mkwrite	= kernfs_vma_page_mkwrite,
 	.access		= kernfs_vma_access,
 };
 
@@ -475,12 +452,17 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
 	if (of->mmapped && of->vm_ops != vma->vm_ops)
 		goto out_put;
 
-	/*
-	 * It is not possible to successfully wrap close.
-	 * So error if someone is trying to use close.
-	 */
-	if (vma->vm_ops && vma->vm_ops->close)
-		goto out_put;
+	if (vma->vm_ops) {
+		/*
+		 * It is not possible to successfully wrap close.
+		 * So error if someone is trying to use close.
+		 */
+		if (vma->vm_ops->close)
+			goto out_put;
+
+		if (WARN_ON_ONCE(vma->vm_ops->page_mkwrite))
+			goto out_put;
+	}
 
 	rc = 0;
 	if (!of->mmapped) {
-- 
2.34.1