Re: [PATCH v3 1/2] sysfs: Invoke iomem_get_mapping() from the sysfs open callback

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Jul 29, 2021 at 11:32:34PM +0000, Krzysztof Wilczyński wrote:
> Defer invocation of the iomem_get_mapping() to the sysfs open callback
> so that it can be executed as needed when the binary sysfs object has
> been accessed.
> 
> To do that, convert the "mapping" member of the struct bin_attribute
> from a pointer to the struct address_space into a function pointer with
> a signature that requires the same return type, and then updates the
> sysfs_kf_bin_open() to invoke provided function should the function
> pointer be valid.
> 
> Also, convert every invocation of iomem_get_mapping() into a function
> pointer assignment, therefore allowing for the iomem_get_mapping()
> invocation to be deferred to when the sysfs open callback runs.
> 
> Thus, this change removes the need for the fs_initcalls to complete
> before any other sub-system that uses the iomem_get_mapping() would be
> able to invoke it safely without leading to a failure and an Oops
> related to an invalid iomem_get_mapping() access.
> 
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/pci/pci-sysfs.c | 6 +++---
>  fs/sysfs/file.c         | 2 +-
>  include/linux/sysfs.h   | 2 +-
>  3 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 5d63df7c1820..76e5545d0e73 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -965,7 +965,7 @@ void pci_create_legacy_files(struct pci_bus *b)
>  	b->legacy_io->read = pci_read_legacy_io;
>  	b->legacy_io->write = pci_write_legacy_io;
>  	b->legacy_io->mmap = pci_mmap_legacy_io;
> -	b->legacy_io->mapping = iomem_get_mapping();
> +	b->legacy_io->mapping = iomem_get_mapping;
>  	pci_adjust_legacy_attr(b, pci_mmap_io);
>  	error = device_create_bin_file(&b->dev, b->legacy_io);
>  	if (error)
> @@ -978,7 +978,7 @@ void pci_create_legacy_files(struct pci_bus *b)
>  	b->legacy_mem->size = 1024*1024;
>  	b->legacy_mem->attr.mode = 0600;
>  	b->legacy_mem->mmap = pci_mmap_legacy_mem;
> -	b->legacy_io->mapping = iomem_get_mapping();
> +	b->legacy_io->mapping = iomem_get_mapping;
>  	pci_adjust_legacy_attr(b, pci_mmap_mem);
>  	error = device_create_bin_file(&b->dev, b->legacy_mem);
>  	if (error)
> @@ -1195,7 +1195,7 @@ static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine)
>  		}
>  	}
>  	if (res_attr->mmap)
> -		res_attr->mapping = iomem_get_mapping();
> +		res_attr->mapping = iomem_get_mapping;
>  	res_attr->attr.name = res_attr_name;
>  	res_attr->attr.mode = 0600;
>  	res_attr->size = pci_resource_len(pdev, num);
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index 9aefa7779b29..a3ee4c32a264 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -175,7 +175,7 @@ static int sysfs_kf_bin_open(struct kernfs_open_file *of)
>  	struct bin_attribute *battr = of->kn->priv;
>  
>  	if (battr->mapping)
> -		of->file->f_mapping = battr->mapping;
> +		of->file->f_mapping = battr->mapping();
>  
>  	return 0;
>  }
> diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> index a12556a4b93a..d5bcc897583c 100644
> --- a/include/linux/sysfs.h
> +++ b/include/linux/sysfs.h
> @@ -176,7 +176,7 @@ struct bin_attribute {
>  	struct attribute	attr;
>  	size_t			size;
>  	void			*private;
> -	struct address_space	*mapping;
> +	struct address_space *(*mapping)(void);
>  	ssize_t (*read)(struct file *, struct kobject *, struct bin_attribute *,
>  			char *, loff_t, size_t);
>  	ssize_t (*write)(struct file *, struct kobject *, struct bin_attribute *,
> -- 
> 2.32.0
>