Re: [PATCH v4 10/21] fs: afs: restore mmap_prepare implementation

Vlastimil Babka (SUSE)
2026-03-25T09:47:35Z

On 3/20/26 23:39, Lorenzo Stoakes (Oracle) wrote:
> Commit 9d5403b1036c ("fs: convert most other generic_file_*mmap() users to
> .mmap_prepare()") updated AFS to use the mmap_prepare callback in favour
> of the deprecated mmap callback.
>
> However, it did not account for the fact that mmap_prepare is called
> pre-merge, and may then be merged, nor that mmap_prepare can fail to map
> due to an out of memory error.
>
> This change was therefore since reverted.
>
> Both of those are cases in which we should not be incrementing a reference
> count.
>
> With the newly added vm_ops->mapped callback available, we can simply
> defer this operation to that callback which is only invoked once the
> mapping is successfully in place (but not yet visible to userspace as the
> mmap and VMA write locks are held).
>
> This allows us to once again reimplement the .mmap_prepare implementation
> for this file system.
>
> Therefore add afs_mapped() to implement this callback for AFS, and remove
> the code doing so in afs_mmap_prepare().
>
> Also update afs_vm_open(), afs_vm_close() and afs_vm_map_pages() to be
> consistent in how the vnode is accessed.
>
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Yep that should take care of that reference count problem.

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

> ---
> fs/afs/file.c | 42 +++++++++++++++++++++++++++++-------------
> 1 file changed, 29 insertions(+), 13 deletions(-)
>
> diff --git a/fs/afs/file.c b/fs/afs/file.c
> index 74d04af51ff4..85696ac984cc 100644
> --- a/fs/afs/file.c
> +++ b/fs/afs/file.c
> @@ -19,7 +19,7 @@
> #include <trace/events/netfs.h>
> #include "internal.h"
>
> -static int afs_file_mmap(struct file *file, struct vm_area_struct *vma);
> +static int afs_file_mmap_prepare(struct vm_area_desc *desc);
>
> static ssize_t afs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter);
> static ssize_t afs_file_splice_read(struct file *in, loff_t *ppos,
> @@ -28,6 +28,8 @@ static ssize_t afs_file_splice_read(struct file *in, loff_t *ppos,
> static void afs_vm_open(struct vm_area_struct *area);
> static void afs_vm_close(struct vm_area_struct *area);
> static vm_fault_t afs_vm_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff);
> +static int afs_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
> + const struct file *file, void **vm_private_data);
>
> const struct file_operations afs_file_operations = {
> .open = afs_open,
> @@ -35,7 +37,7 @@ const struct file_operations afs_file_operations = {
> .llseek = generic_file_llseek,
> .read_iter = afs_file_read_iter,
> .write_iter = netfs_file_write_iter,
> - .mmap = afs_file_mmap,
> + .mmap_prepare = afs_file_mmap_prepare,
> .splice_read = afs_file_splice_read,
> .splice_write = iter_file_splice_write,
> .fsync = afs_fsync,
> @@ -61,6 +63,7 @@ const struct address_space_operations afs_file_aops = {
> };
>
> static const struct vm_operations_struct afs_vm_ops = {
> + .mapped = afs_mapped,
> .open = afs_vm_open,
> .close = afs_vm_close,
> .fault = filemap_fault,
> @@ -492,34 +495,47 @@ static void afs_drop_open_mmap(struct afs_vnode *vnode)
> /*
> * Handle setting up a memory mapping on an AFS file.
> */
> -static int afs_file_mmap(struct file *file, struct vm_area_struct *vma)
> +static int afs_file_mmap_prepare(struct vm_area_desc *desc)
> {
> - struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
> int ret;
>
> - afs_add_open_mmap(vnode);
> + ret = generic_file_mmap_prepare(desc);
> + if (ret)
> + return ret;
>
> - ret = generic_file_mmap(file, vma);
> - if (ret == 0)
> - vma->vm_ops = &afs_vm_ops;
> - else
> - afs_drop_open_mmap(vnode);
> + desc->vm_ops = &afs_vm_ops;
> return ret;
> }
>
> +static int afs_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
> + const struct file *file, void **vm_private_data)
> +{
> + struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
> +
> + afs_add_open_mmap(vnode);
> + return 0;
> +}
> +
> static void afs_vm_open(struct vm_area_struct *vma)
> {
> - afs_add_open_mmap(AFS_FS_I(file_inode(vma->vm_file)));
> + struct file *file = vma->vm_file;
> + struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
> +
> + afs_add_open_mmap(vnode);
> }
>
> static void afs_vm_close(struct vm_area_struct *vma)
> {
> - afs_drop_open_mmap(AFS_FS_I(file_inode(vma->vm_file)));
> + struct file *file = vma->vm_file;
> + struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
> +
> + afs_drop_open_mmap(vnode);
> }
>
> static vm_fault_t afs_vm_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff)
> {
> - struct afs_vnode *vnode = AFS_FS_I(file_inode(vmf->vma->vm_file));
> + struct file *file = vmf->vma->vm_file;
> + struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
>
> if (afs_check_validity(vnode))
> return filemap_map_pages(vmf, start_pgoff, end_pgoff);
> --
> 2.53.0