Re: [PATCH v2 1/4] kernfs: remove page_mkwrite() from vm_operations_struct

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On 6/11/24 11:27 AM, Martin Oliveira wrote:
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 return -EINVAL if an
mmap() implementation sets .page_mkwrite.

Hi Martin and Logan!

First of all, I admire this approach to solving one of the gup+filesystem
interaction problems, by coming in from the other direction. Neat. :)



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 | 26 +++-----------------------
  1 file changed, 3 insertions(+), 23 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 8502ef68459b9..a198cb0718772 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 +459,9 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
  	if (vma->vm_ops && vma->vm_ops->close)
  		goto out_put;
+ if (vma->vm_ops->page_mkwrite)

As the kernel test bot results imply, you probably want to do it like this:

   	if (vma->vm_ops && vma->vm_ops->page_mkwrite)


+		goto out_put;
+
  	rc = 0;
  	if (!of->mmapped) {
  		of->mmapped = true;

thanks,
--
John Hubbard
NVIDIA





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