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

From: Martin Oliveira
Date: Mon Jul 08 2024 - 12:58:01 EST


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