[PATCH v2] mm: Change return type to vm_fault_t

[PATCH v2] mm: Change return type to vm_fault_t

[Souptick Joarder]

Use new return type vm_fault_t for fault handler
in struct vm_operations_struct. For now, this is
just documenting that the function returns a 
VM_FAULT value rather than an errno.  Once all
instances are converted, vm_fault_t will become
a distinct type.

commit 1c8f422059ae ("mm: change return type to
vm_fault_t")

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
---
v2: Updated the change log

 mm/hugetlb.c | 2 +-
 mm/mmap.c    | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7c204e3..acb432a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3158,7 +3158,7 @@ static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
  * hugegpage VMA.  do_page_fault() is supposed to trap this, so BUG is we get
  * this far.
  */
-static int hugetlb_vm_op_fault(struct vm_fault *vmf)
+static vm_fault_t hugetlb_vm_op_fault(struct vm_fault *vmf)
 {
 	BUG();
 	return 0;
diff --git a/mm/mmap.c b/mm/mmap.c
index 9efdc021..ac41b34 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3208,7 +3208,7 @@ void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
 		mm->data_vm += npages;
 }
 
-static int special_mapping_fault(struct vm_fault *vmf);
+static vm_fault_t special_mapping_fault(struct vm_fault *vmf);
 
 /*
  * Having a close hook prevents vma merging regardless of flags.
@@ -3247,7 +3247,7 @@ static int special_mapping_mremap(struct vm_area_struct *new_vma)
 	.fault = special_mapping_fault,
 };
 
-static int special_mapping_fault(struct vm_fault *vmf)
+static vm_fault_t special_mapping_fault(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	pgoff_t pgoff;
-- 
1.9.1

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

[Matthew Wilcox]

On Fri, May 11, 2018 at 11:36:39PM +0530, Souptick Joarder wrote:
>  mm/hugetlb.c | 2 +-
>  mm/mmap.c    | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)

Don't we also need to convert include/linux/mm_types.h:

@@ -621,7 +621,7 @@ struct vm_special_mapping {
         * If non-NULL, then this is called to resolve page faults
         * on the special mapping.  If used, .pages is not checked.
         */
-       int (*fault)(const struct vm_special_mapping *sm,
+       vm_fault_t (*fault)(const struct vm_special_mapping *sm,
                     struct vm_area_struct *vma,
                     struct vm_fault *vmf);
 
or are you leaving that for a later patch?

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

[Souptick Joarder]

On Fri, May 11, 2018 at 11:45 PM, Matthew Wilcox <willy@infradead.org> wrote:
> On Fri, May 11, 2018 at 11:36:39PM +0530, Souptick Joarder wrote:
>>  mm/hugetlb.c | 2 +-
>>  mm/mmap.c    | 4 ++--
>>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> Don't we also need to convert include/linux/mm_types.h:
>
> @@ -621,7 +621,7 @@ struct vm_special_mapping {
>          * If non-NULL, then this is called to resolve page faults
>          * on the special mapping.  If used, .pages is not checked.
>          */
> -       int (*fault)(const struct vm_special_mapping *sm,
> +       vm_fault_t (*fault)(const struct vm_special_mapping *sm,
>                      struct vm_area_struct *vma,
>                      struct vm_fault *vmf);
>
> or are you leaving that for a later patch?

Ahh, I didn't realise. No I think, we can add it as part of this
patch. Will send v3.

[PATCH v2] mm: Change return type to vm_fault_t

[Souptick Joarder]

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.

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

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

[Michal Hocko]

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