Re: [PATCH v2] mm: Change return type to vm_fault_t

[Michal Hocko <mhocko@kernel.org>]

On Sat 10-03-18 21:53:52, Souptick Joarder wrote:
> The plan for these patches is to introduce the typedef, initially
> just as documentation ("These functions should return a VM_FAULT_ status").
> We'll trickle the patches to individual drivers/filesystems in through
> the maintainers, as far as possible. Then we'll change the typedef
> to an unsigned int and break the compilation of any unconverted
> drivers/filesystems.
> 
> vmf_insert_page(), vmf_insert_mixed() and vmf_insert_pfn() are three
> newly added functions. The various drivers/filesystems where return value
> of fault(), huge_fault(), page_mkwrite() and pfn_mkwrite() get converted,
> will need them. These functions will return correct VM_FAULT_ code based
> on err value.
> 
> We've had bugs before where drivers returned -EFOO.  And we have this
> silly inefficiency where vm_insert_xxx() return an errno which (afaict)
> every driver then converts into a VM_FAULT code. In many cases drivers
> failed to return correct VM_FAULT code value despite of vm_insert_xxx()
> fails. We have indentified and clean up all those existing bugs and silly
> inefficiencies in driver/filesystems by adding these three new inline
> wrappers. As mentioned above, we will trickle those patches to individual
> drivers/filesystems in through maintainers after these three wrapper
> functions are merged.
> 
> Eventually we can convert vm_insert_xxx() into vmf_insert_xxx() and
> remove these inline wrappers, but these are a good intermediate step.

Yes, this makes sense to me. 3 copies of error->vmfault conversion hurt
eyes a bit, though

> Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>

Anyway, feel free to add
Acked-by: Michal Hocko <mhocko@suse.com>

and good luck with conversions.

> ---
>  include/linux/mm.h       | 47 +++++++++++++++++++++++++++++++++++++++++++----
>  include/linux/mm_types.h |  2 ++
>  2 files changed, 45 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ad06d42..a4d8853 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -379,17 +379,18 @@ struct vm_operations_struct {
>  	void (*close)(struct vm_area_struct * area);
>  	int (*split)(struct vm_area_struct * area, unsigned long addr);
>  	int (*mremap)(struct vm_area_struct * area);
> -	int (*fault)(struct vm_fault *vmf);
> -	int (*huge_fault)(struct vm_fault *vmf, enum page_entry_size pe_size);
> +	vm_fault_t (*fault)(struct vm_fault *vmf);
> +	vm_fault_t (*huge_fault)(struct vm_fault *vmf,
> +			enum page_entry_size pe_size);
>  	void (*map_pages)(struct vm_fault *vmf,
>  			pgoff_t start_pgoff, pgoff_t end_pgoff);
> 
>  	/* notification that a previously read-only page is about to become
>  	 * writable, if an error is returned it will cause a SIGBUS */
> -	int (*page_mkwrite)(struct vm_fault *vmf);
> +	vm_fault_t (*page_mkwrite)(struct vm_fault *vmf);
> 
>  	/* same as page_mkwrite when using VM_PFNMAP|VM_MIXEDMAP */
> -	int (*pfn_mkwrite)(struct vm_fault *vmf);
> +	vm_fault_t (*pfn_mkwrite)(struct vm_fault *vmf);
> 
>  	/* called by access_process_vm when get_user_pages() fails, typically
>  	 * for use by special VMAs that can switch between memory and hardware
> @@ -2413,6 +2414,44 @@ int vm_insert_mixed_mkwrite(struct vm_area_struct *vma, unsigned long addr,
>  			pfn_t pfn);
>  int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len);
> 
> +static inline vm_fault_t vmf_insert_page(struct vm_area_struct *vma,
> +				unsigned long addr, struct page *page)
> +{
> +	int err = vm_insert_page(vma, addr, page);
> +
> +	if (err == -ENOMEM)
> +		return VM_FAULT_OOM;
> +	if (err < 0 && err != -EBUSY)
> +		return VM_FAULT_SIGBUS;
> +
> +	return VM_FAULT_NOPAGE;
> +}
> +
> +static inline vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma,
> +				unsigned long addr, pfn_t pfn)
> +{
> +	int err = vm_insert_mixed(vma, addr, pfn);
> +
> +	if (err == -ENOMEM)
> +		return VM_FAULT_OOM;
> +	if (err < 0 && err != -EBUSY)
> +		return VM_FAULT_SIGBUS;
> +
> +	return VM_FAULT_NOPAGE;
> +}
> +
> +static inline vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma,
> +			unsigned long addr, unsigned long pfn)
> +{
> +	int err = vm_insert_pfn(vma, addr, pfn);
> +
> +	if (err == -ENOMEM)
> +		return VM_FAULT_OOM;
> +	if (err < 0 && err != -EBUSY)
> +		return VM_FAULT_SIGBUS;
> +
> +	return VM_FAULT_NOPAGE;
> +}
> 
>  struct page *follow_page_mask(struct vm_area_struct *vma,
>  			      unsigned long address, unsigned int foll_flags,
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index fd1af6b..2161234 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -22,6 +22,8 @@
>  #endif
>  #define AT_VECTOR_SIZE (2*(AT_VECTOR_SIZE_ARCH + AT_VECTOR_SIZE_BASE + 1))
> 
> +typedef int vm_fault_t;
> +
>  struct address_space;
>  struct mem_cgroup;
>  struct hmm;
> --
> 1.9.1

-- 
Michal Hocko
SUSE Labs