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SubjectRe: [RFC PATCH V2 09/12] fs: Prevent mode change if file is mmap'ed
On Fri, Jan 10, 2020 at 11:29:39AM -0800, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> Page faults need to ensure the inode mode is correct and consistent with
> the vmf information at the time of the fault. There is no easy way to
> ensure the vmf information is correct if a mode change is in progress.
> Furthermore, there is no good use case to require a mode change while
> the file is mmap'ed.
>
> Track mmap's of the file and fail the mode change if the file is
> mmap'ed.
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> ---
> fs/inode.c | 2 ++
> fs/xfs/xfs_ioctl.c | 8 ++++++++
> include/linux/fs.h | 1 +
> mm/mmap.c | 19 +++++++++++++++++--
> 4 files changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/fs/inode.c b/fs/inode.c
> index 2b0f51161918..944711aed6f8 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -245,6 +245,8 @@ static struct inode *alloc_inode(struct super_block *sb)
> return NULL;
> }
>
> + atomic64_set(&inode->i_mapped, 0);
> +
> return inode;
> }
>
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index bc3654fe3b5d..1ab0906c6c7f 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1200,6 +1200,14 @@ xfs_ioctl_setattr_dax_invalidate(
> goto out_unlock;
> }
>
> + /*
> + * If there is a mapping in place we must remain in our current mode.
> + */
> + if (atomic64_read(&inode->i_mapped)) {

Urk, should we really be messing around with the address space
internals?

> + error = -EBUSY;
> + goto out_unlock;
> + }
> +
> error = filemap_write_and_wait(inode->i_mapping);
> if (error)
> goto out_unlock;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 631f11d6246e..6e7dc626b657 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -740,6 +740,7 @@ struct inode {
> #endif
>
> void *i_private; /* fs or device private pointer */
> + atomic64_t i_mapped;

I would have expected to find this in struct address_space since the
mapping count is a function of the address space, right?

--D

> } __randomize_layout;
>
> struct timespec64 timestamp_truncate(struct timespec64 t, struct inode *inode);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index dfaf1130e706..e6b68924b7ca 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -171,12 +171,17 @@ void unlink_file_vma(struct vm_area_struct *vma)
> static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
> {
> struct vm_area_struct *next = vma->vm_next;
> + struct file *f = vma->vm_file;
>
> might_sleep();
> if (vma->vm_ops && vma->vm_ops->close)
> vma->vm_ops->close(vma);
> - if (vma->vm_file)
> - fput(vma->vm_file);
> + if (f) {
> + struct inode *inode = file_inode(f);
> + if (inode)
> + atomic64_dec(&inode->i_mapped);
> + fput(f);
> + }
> mpol_put(vma_policy(vma));
> vm_area_free(vma);
> return next;
> @@ -1837,6 +1842,16 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>
> vma_set_page_prot(vma);
>
> + /*
> + * Track if there is mapping in place such that a mode change
> + * does not occur on a file which is mapped
> + */
> + if (file) {
> + struct inode *inode = file_inode(file);
> +
> + atomic64_inc(&inode->i_mapped);
> + }
> +
> return addr;
>
> unmap_and_free_vma:
> --
> 2.21.0
>

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