linux-kernel - [PATCH v3 1/3] kernfs: remove page_mkwrite() from vm_operations

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Message-Id: <20240704163724.2462161-2-martin.oliveira@eideticom.com>
Date: Thu,  4 Jul 2024 10:37:22 -0600
From: Martin Oliveira <martin.oliveira@...eticom.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-rdma@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Artemy Kovalyov <artemyko@...dia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Leon Romanovsky <leon@...nel.org>,
	Logan Gunthorpe <logang@...tatee.com>,
	Martin Oliveira <martin.oliveira@...eticom.com>,
	Michael Guralnik <michaelgur@...dia.com>,
	Mike Marciniszyn <mike.marciniszyn@...el.com>,
	Shiraz Saleem <shiraz.saleem@...el.com>,
	Tejun Heo <tj@...nel.org>,
	John Hubbard <jhubbard@...dia.com>,
	Dan Williams <dan.j.williams@...el.com>,
	David Sloan <david.sloan@...eticom.com>
Subject: [PATCH v3 1/3] kernfs: remove page_mkwrite() from vm_operations_struct

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_ON() if an mmap()
implementation sets .page_mkwrite.

Co-developed-by: Logan Gunthorpe <logang@...tatee.com>
Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
Signed-off-by: Martin Oliveira <martin.oliveira@...eticom.com>
---
 fs/kernfs/file.c | 25 ++-----------------------
 1 file changed, 2 insertions(+), 23 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 8502ef68459b..90603664de7f 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,
 };
 
@@ -482,6 +459,8 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
 	if (vma->vm_ops && vma->vm_ops->close)
 		goto out_put;
 
+	WARN_ON(vma->vm_ops && vma->vm_ops->page_mkwrite);
+
 	rc = 0;
 	if (!of->mmapped) {
 		of->mmapped = true;
-- 
2.34.1