[PATCH] mm: Create the new vm_fault_t type

[PATCH] mm: Create the new vm_fault_t type

[Souptick Joarder]

Page fault handlers are supposed to return VM_FAULT codes,
but some drivers/file systems mistakenly return error
numbers. Now that all drivers/file systems have been converted
to use the vm_fault_t return type, change the type definition
to no longer be compatible with 'int'. By making it an unsigned
int, the function prototype becomes incompatible with a function
which returns int. Sparse will detect any attempts to return a
value which is not a VM_FAULT code.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
---
 include/linux/mm.h       | 46 -----------------------------
 include/linux/mm_types.h | 75 +++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 74 insertions(+), 47 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index fcf9cc9..511a3ce 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1267,52 +1267,6 @@ static inline void clear_page_pfmemalloc(struct page *page)
 }
 
 /*
- * Different kinds of faults, as returned by handle_mm_fault().
- * Used to decide whether a process gets delivered SIGBUS or
- * just gets major/minor fault counters bumped up.
- */
-
-#define VM_FAULT_OOM	0x0001
-#define VM_FAULT_SIGBUS	0x0002
-#define VM_FAULT_MAJOR	0x0004
-#define VM_FAULT_WRITE	0x0008	/* Special case for get_user_pages */
-#define VM_FAULT_HWPOISON 0x0010	/* Hit poisoned small page */
-#define VM_FAULT_HWPOISON_LARGE 0x0020  /* Hit poisoned large page. Index encoded in upper bits */
-#define VM_FAULT_SIGSEGV 0x0040
-
-#define VM_FAULT_NOPAGE	0x0100	/* ->fault installed the pte, not return page */
-#define VM_FAULT_LOCKED	0x0200	/* ->fault locked the returned page */
-#define VM_FAULT_RETRY	0x0400	/* ->fault blocked, must retry */
-#define VM_FAULT_FALLBACK 0x0800	/* huge page fault failed, fall back to small */
-#define VM_FAULT_DONE_COW   0x1000	/* ->fault has fully handled COW */
-#define VM_FAULT_NEEDDSYNC  0x2000	/* ->fault did not modify page tables
-					 * and needs fsync() to complete (for
-					 * synchronous page faults in DAX) */
-
-#define VM_FAULT_ERROR	(VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | \
-			 VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \
-			 VM_FAULT_FALLBACK)
-
-#define VM_FAULT_RESULT_TRACE \
-	{ VM_FAULT_OOM,			"OOM" }, \
-	{ VM_FAULT_SIGBUS,		"SIGBUS" }, \
-	{ VM_FAULT_MAJOR,		"MAJOR" }, \
-	{ VM_FAULT_WRITE,		"WRITE" }, \
-	{ VM_FAULT_HWPOISON,		"HWPOISON" }, \
-	{ VM_FAULT_HWPOISON_LARGE,	"HWPOISON_LARGE" }, \
-	{ VM_FAULT_SIGSEGV,		"SIGSEGV" }, \
-	{ VM_FAULT_NOPAGE,		"NOPAGE" }, \
-	{ VM_FAULT_LOCKED,		"LOCKED" }, \
-	{ VM_FAULT_RETRY,		"RETRY" }, \
-	{ VM_FAULT_FALLBACK,		"FALLBACK" }, \
-	{ VM_FAULT_DONE_COW,		"DONE_COW" }, \
-	{ VM_FAULT_NEEDDSYNC,		"NEEDDSYNC" }
-
-/* Encode hstate index for a hwpoisoned large page */
-#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
-#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
-
-/*
  * Can be called by the pagefault handler when it gets a VM_FAULT_OOM.
  */
 extern void pagefault_out_of_memory(void);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5ed8f62..48c2108 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -22,7 +22,6 @@
 #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;
@@ -609,6 +608,80 @@ static inline bool mm_tlb_flush_nested(struct mm_struct *mm)
 
 struct vm_fault;
 
+/**
+ * typedef vm_fault_t -  __bitwise unsigned int
+ *
+ * vm_fault_t is the new unsigned int type to return VM_FAULT
+ * code by page fault handlers of drivers/file systems. Now if
+ * any page fault handlers returns non VM_FAULT code instead
+ * of VM_FAULT code, it will be a mismatch with function
+ * prototype and sparse will detect it.
+ */
+typedef __bitwise unsigned int vm_fault_t;
+
+/**
+ * enum - VM_FAULT code
+ *
+ * This enum is used to track the VM_FAULT code return by page
+ * fault handlers.
+ *
+ * @VM_FAULT_OOM:		Out Of Memory
+ * @VM_FAULT_SIGBUS:		Bad access
+ * @VM_FAULT_MAJOR:		Page read from storage
+ * @VM_FAULT_WRITE:		Special case for get_user_pages
+ * @VM_FAULT_HWPOISON:		Hit poisoned small page
+ * @VM_FAULT_HWPOISON_LARGE:	Hit poisoned large page. Index encoded
+ *				in upper bits
+ * @VM_FAULT_SIGSEGV:		segmentation fault
+ * @VM_FAULT_NOPAGE:		->fault installed the pte, not return page
+ * @VM_FAULT_LOCKED:		->fault locked the returned page
+ * @VM_FAULT_RETRY:		->fault blocked, must retry
+ * @VM_FAULT_FALLBACK:		huge page fault failed, fall back to small
+ * @VM_FAULT_DONE_COW:		->fault has fully handled COW
+ * @VM_FAULT_NEEDDSYNC:		->fault did not modify page tables and needs
+ *				fsync() to complete (for synchronous page faults
+ *				in DAX)
+ */
+enum {
+	VM_FAULT_OOM            = (__force vm_fault_t)0x000001,
+	VM_FAULT_SIGBUS         = (__force vm_fault_t)0x000002,
+	VM_FAULT_MAJOR          = (__force vm_fault_t)0x000004,
+	VM_FAULT_WRITE          = (__force vm_fault_t)0x000008,
+	VM_FAULT_HWPOISON       = (__force vm_fault_t)0x000010,
+	VM_FAULT_HWPOISON_LARGE = (__force vm_fault_t)0x000020,
+	VM_FAULT_SIGSEGV        = (__force vm_fault_t)0x000040,
+	VM_FAULT_NOPAGE         = (__force vm_fault_t)0x000100,
+	VM_FAULT_LOCKED         = (__force vm_fault_t)0x000200,
+	VM_FAULT_RETRY          = (__force vm_fault_t)0x000400,
+	VM_FAULT_FALLBACK       = (__force vm_fault_t)0x000800,
+	VM_FAULT_DONE_COW       = (__force vm_fault_t)0x001000,
+	VM_FAULT_NEEDDSYNC      = (__force vm_fault_t)0x002000,
+	VM_FAULT_HINDEX_MASK    = (__force vm_fault_t)0x0f0000,
+};
+
+/* Encode hstate index for a hwpoisoned large page */
+#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
+#define VM_FAULT_GET_HINDEX(x) (((x) >> 16) & 0xf)
+
+#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS |	\
+			VM_FAULT_SIGSEGV | VM_FAULT_HWPOISON |	\
+			VM_FAULT_HWPOISON_LARGE | VM_FAULT_FALLBACK)
+
+#define VM_FAULT_RESULT_TRACE \
+	{ VM_FAULT_OOM,                 "OOM" },	\
+	{ VM_FAULT_SIGBUS,              "SIGBUS" },	\
+	{ VM_FAULT_MAJOR,               "MAJOR" },	\
+	{ VM_FAULT_WRITE,               "WRITE" },	\
+	{ VM_FAULT_HWPOISON,            "HWPOISON" },	\
+	{ VM_FAULT_HWPOISON_LARGE,      "HWPOISON_LARGE" },	\
+	{ VM_FAULT_SIGSEGV,             "SIGSEGV" },	\
+	{ VM_FAULT_NOPAGE,              "NOPAGE" },	\
+	{ VM_FAULT_LOCKED,              "LOCKED" },	\
+	{ VM_FAULT_RETRY,               "RETRY" },	\
+	{ VM_FAULT_FALLBACK,            "FALLBACK" },	\
+	{ VM_FAULT_DONE_COW,            "DONE_COW" },	\
+	{ VM_FAULT_NEEDDSYNC,           "NEEDDSYNC" }
+
 struct vm_special_mapping {
 	const char *name;	/* The name, e.g. "[vdso]". */
 
-- 
1.9.1

Re: [PATCH] mm: Create the new vm_fault_t type

[Souptick Joarder]

On Sat, Nov 3, 2018 at 10:31 AM Souptick Joarder <jrdr.linux@gmail.com> wrote:
>
> Page fault handlers are supposed to return VM_FAULT codes,
> but some drivers/file systems mistakenly return error
> numbers. Now that all drivers/file systems have been converted
> to use the vm_fault_t return type, change the type definition
> to no longer be compatible with 'int'. By making it an unsigned
> int, the function prototype becomes incompatible with a function
> which returns int. Sparse will detect any attempts to return a
> value which is not a VM_FAULT code.
>
> Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
> ---
>  include/linux/mm.h       | 46 -----------------------------
>  include/linux/mm_types.h | 75 +++++++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 74 insertions(+), 47 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index fcf9cc9..511a3ce 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1267,52 +1267,6 @@ static inline void clear_page_pfmemalloc(struct page *page)
>  }
>
>  /*
> - * Different kinds of faults, as returned by handle_mm_fault().
> - * Used to decide whether a process gets delivered SIGBUS or
> - * just gets major/minor fault counters bumped up.
> - */
> -
> -#define VM_FAULT_OOM   0x0001
> -#define VM_FAULT_SIGBUS        0x0002
> -#define VM_FAULT_MAJOR 0x0004
> -#define VM_FAULT_WRITE 0x0008  /* Special case for get_user_pages */
> -#define VM_FAULT_HWPOISON 0x0010       /* Hit poisoned small page */
> -#define VM_FAULT_HWPOISON_LARGE 0x0020  /* Hit poisoned large page. Index encoded in upper bits */
> -#define VM_FAULT_SIGSEGV 0x0040
> -
> -#define VM_FAULT_NOPAGE        0x0100  /* ->fault installed the pte, not return page */
> -#define VM_FAULT_LOCKED        0x0200  /* ->fault locked the returned page */
> -#define VM_FAULT_RETRY 0x0400  /* ->fault blocked, must retry */
> -#define VM_FAULT_FALLBACK 0x0800       /* huge page fault failed, fall back to small */
> -#define VM_FAULT_DONE_COW   0x1000     /* ->fault has fully handled COW */
> -#define VM_FAULT_NEEDDSYNC  0x2000     /* ->fault did not modify page tables
> -                                        * and needs fsync() to complete (for
> -                                        * synchronous page faults in DAX) */
> -
> -#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | \
> -                        VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \
> -                        VM_FAULT_FALLBACK)
> -
> -#define VM_FAULT_RESULT_TRACE \
> -       { VM_FAULT_OOM,                 "OOM" }, \
> -       { VM_FAULT_SIGBUS,              "SIGBUS" }, \
> -       { VM_FAULT_MAJOR,               "MAJOR" }, \
> -       { VM_FAULT_WRITE,               "WRITE" }, \
> -       { VM_FAULT_HWPOISON,            "HWPOISON" }, \
> -       { VM_FAULT_HWPOISON_LARGE,      "HWPOISON_LARGE" }, \
> -       { VM_FAULT_SIGSEGV,             "SIGSEGV" }, \
> -       { VM_FAULT_NOPAGE,              "NOPAGE" }, \
> -       { VM_FAULT_LOCKED,              "LOCKED" }, \
> -       { VM_FAULT_RETRY,               "RETRY" }, \
> -       { VM_FAULT_FALLBACK,            "FALLBACK" }, \
> -       { VM_FAULT_DONE_COW,            "DONE_COW" }, \
> -       { VM_FAULT_NEEDDSYNC,           "NEEDDSYNC" }
> -
> -/* Encode hstate index for a hwpoisoned large page */
> -#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
> -#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
> -
> -/*
>   * Can be called by the pagefault handler when it gets a VM_FAULT_OOM.
>   */
>  extern void pagefault_out_of_memory(void);
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 5ed8f62..48c2108 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -22,7 +22,6 @@
>  #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;
> @@ -609,6 +608,80 @@ static inline bool mm_tlb_flush_nested(struct mm_struct *mm)
>
>  struct vm_fault;
>
> +/**
> + * typedef vm_fault_t -  __bitwise unsigned int
> + *
> + * vm_fault_t is the new unsigned int type to return VM_FAULT
> + * code by page fault handlers of drivers/file systems. Now if
> + * any page fault handlers returns non VM_FAULT code instead
> + * of VM_FAULT code, it will be a mismatch with function
> + * prototype and sparse will detect it.
> + */
> +typedef __bitwise unsigned int vm_fault_t;
> +
> +/**
> + * enum - VM_FAULT code
> + *
> + * This enum is used to track the VM_FAULT code return by page
> + * fault handlers.
> + *
> + * @VM_FAULT_OOM:              Out Of Memory
> + * @VM_FAULT_SIGBUS:           Bad access
> + * @VM_FAULT_MAJOR:            Page read from storage
> + * @VM_FAULT_WRITE:            Special case for get_user_pages
> + * @VM_FAULT_HWPOISON:         Hit poisoned small page
> + * @VM_FAULT_HWPOISON_LARGE:   Hit poisoned large page. Index encoded
> + *                             in upper bits
> + * @VM_FAULT_SIGSEGV:          segmentation fault
> + * @VM_FAULT_NOPAGE:           ->fault installed the pte, not return page
> + * @VM_FAULT_LOCKED:           ->fault locked the returned page
> + * @VM_FAULT_RETRY:            ->fault blocked, must retry
> + * @VM_FAULT_FALLBACK:         huge page fault failed, fall back to small
> + * @VM_FAULT_DONE_COW:         ->fault has fully handled COW
> + * @VM_FAULT_NEEDDSYNC:                ->fault did not modify page tables and needs
> + *                             fsync() to complete (for synchronous page faults
> + *                             in DAX)
> + */
> +enum {
> +       VM_FAULT_OOM            = (__force vm_fault_t)0x000001,
> +       VM_FAULT_SIGBUS         = (__force vm_fault_t)0x000002,
> +       VM_FAULT_MAJOR          = (__force vm_fault_t)0x000004,
> +       VM_FAULT_WRITE          = (__force vm_fault_t)0x000008,
> +       VM_FAULT_HWPOISON       = (__force vm_fault_t)0x000010,
> +       VM_FAULT_HWPOISON_LARGE = (__force vm_fault_t)0x000020,
> +       VM_FAULT_SIGSEGV        = (__force vm_fault_t)0x000040,
> +       VM_FAULT_NOPAGE         = (__force vm_fault_t)0x000100,
> +       VM_FAULT_LOCKED         = (__force vm_fault_t)0x000200,
> +       VM_FAULT_RETRY          = (__force vm_fault_t)0x000400,
> +       VM_FAULT_FALLBACK       = (__force vm_fault_t)0x000800,
> +       VM_FAULT_DONE_COW       = (__force vm_fault_t)0x001000,
> +       VM_FAULT_NEEDDSYNC      = (__force vm_fault_t)0x002000,
> +       VM_FAULT_HINDEX_MASK    = (__force vm_fault_t)0x0f0000,
> +};
> +
> +/* Encode hstate index for a hwpoisoned large page */
> +#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
> +#define VM_FAULT_GET_HINDEX(x) (((x) >> 16) & 0xf)
> +
> +#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS |       \
> +                       VM_FAULT_SIGSEGV | VM_FAULT_HWPOISON |  \
> +                       VM_FAULT_HWPOISON_LARGE | VM_FAULT_FALLBACK)
> +
> +#define VM_FAULT_RESULT_TRACE \
> +       { VM_FAULT_OOM,                 "OOM" },        \
> +       { VM_FAULT_SIGBUS,              "SIGBUS" },     \
> +       { VM_FAULT_MAJOR,               "MAJOR" },      \
> +       { VM_FAULT_WRITE,               "WRITE" },      \
> +       { VM_FAULT_HWPOISON,            "HWPOISON" },   \
> +       { VM_FAULT_HWPOISON_LARGE,      "HWPOISON_LARGE" },     \
> +       { VM_FAULT_SIGSEGV,             "SIGSEGV" },    \
> +       { VM_FAULT_NOPAGE,              "NOPAGE" },     \
> +       { VM_FAULT_LOCKED,              "LOCKED" },     \
> +       { VM_FAULT_RETRY,               "RETRY" },      \
> +       { VM_FAULT_FALLBACK,            "FALLBACK" },   \
> +       { VM_FAULT_DONE_COW,            "DONE_COW" },   \
> +       { VM_FAULT_NEEDDSYNC,           "NEEDDSYNC" }
> +

checkpatch.pl is throwing an error "ERROR: Macros with complex values
should be enclosed in parentheses". But if I put it under macro it leads to
compile error for * make allyesconfig * ( x86_64 arch).
That the reason I have ignored the error in checkpatch.pl.

>  struct vm_special_mapping {
>         const char *name;       /* The name, e.g. "[vdso]". */
>
> --
> 1.9.1
>

Re: [PATCH] mm: Create the new vm_fault_t type

[Matthew Wilcox]

On Sat, Nov 03, 2018 at 10:35:04AM +0530, Souptick Joarder wrote:
> Page fault handlers are supposed to return VM_FAULT codes,
> but some drivers/file systems mistakenly return error
> numbers. Now that all drivers/file systems have been converted
> to use the vm_fault_t return type, change the type definition
> to no longer be compatible with 'int'. By making it an unsigned
> int, the function prototype becomes incompatible with a function
> which returns int. Sparse will detect any attempts to return a
> value which is not a VM_FAULT code.


> -/* Encode hstate index for a hwpoisoned large page */
> -#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
> -#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
...
> +/* Encode hstate index for a hwpoisoned large page */
> +#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
> +#define VM_FAULT_GET_HINDEX(x) (((x) >> 16) & 0xf)

I think it's important to mention in the changelog that these values
have been changed to avoid conflicts with other VM_FAULT codes.

> +/**
> + * typedef vm_fault_t -  __bitwise unsigned int
> + *
> + * vm_fault_t is the new unsigned int type to return VM_FAULT
> + * code by page fault handlers of drivers/file systems. Now if
> + * any page fault handlers returns non VM_FAULT code instead
> + * of VM_FAULT code, it will be a mismatch with function
> + * prototype and sparse will detect it.
> + */

The first line should be what the typedef *means*, not repeat the
compiler's definition.  The rest of the description should be information
for someone coming to the type for the first time; what you've written
here is changelog material.

/**
 * typedef vm_fault_t - Return type for page fault handlers.
 *
 * Page fault handlers return a bitmask of %VM_FAULT values.
 */

> +typedef __bitwise unsigned int vm_fault_t;
> +
> +/**
> + * enum - VM_FAULT code

Can you document an anonymous enum?  I've never tried.  Did you run this
through 'make htmldocs'?

> + * This enum is used to track the VM_FAULT code return by page
> + * fault handlers.

 * Page fault handlers return a bitmask of these values to tell the
 * core VM what happened when handling the fault.

Re: [PATCH] mm: Create the new vm_fault_t type

[Mike Rapoport]

On Sat, Nov 03, 2018 at 05:02:36AM -0700, Matthew Wilcox wrote:
> On Sat, Nov 03, 2018 at 10:35:04AM +0530, Souptick Joarder wrote:
> > Page fault handlers are supposed to return VM_FAULT codes,
> > but some drivers/file systems mistakenly return error
> > numbers. Now that all drivers/file systems have been converted
> > to use the vm_fault_t return type, change the type definition
> > to no longer be compatible with 'int'. By making it an unsigned
> > int, the function prototype becomes incompatible with a function
> > which returns int. Sparse will detect any attempts to return a
> > value which is not a VM_FAULT code.
> 
> 
> > -/* Encode hstate index for a hwpoisoned large page */
> > -#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
> > -#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
> ...
> > +/* Encode hstate index for a hwpoisoned large page */
> > +#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
> > +#define VM_FAULT_GET_HINDEX(x) (((x) >> 16) & 0xf)
> 
> I think it's important to mention in the changelog that these values
> have been changed to avoid conflicts with other VM_FAULT codes.
> 
> > +/**
> > + * typedef vm_fault_t -  __bitwise unsigned int
> > + *
> > + * vm_fault_t is the new unsigned int type to return VM_FAULT
> > + * code by page fault handlers of drivers/file systems. Now if
> > + * any page fault handlers returns non VM_FAULT code instead
> > + * of VM_FAULT code, it will be a mismatch with function
> > + * prototype and sparse will detect it.
> > + */
> 
> The first line should be what the typedef *means*, not repeat the
> compiler's definition.  The rest of the description should be information
> for someone coming to the type for the first time; what you've written
> here is changelog material.
> 
> /**
>  * typedef vm_fault_t - Return type for page fault handlers.
>  *
>  * Page fault handlers return a bitmask of %VM_FAULT values.
>  */
> 
> > +typedef __bitwise unsigned int vm_fault_t;
> > +
> > +/**
> > + * enum - VM_FAULT code
> 
> Can you document an anonymous enum?  I've never tried.  Did you run this
> through 'make htmldocs'?

You cannot document an anonymous enum.
 
> > + * This enum is used to track the VM_FAULT code return by page
> > + * fault handlers.
> 
>  * Page fault handlers return a bitmask of these values to tell the
>  * core VM what happened when handling the fault.
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH] mm: Create the new vm_fault_t type

[Souptick Joarder]

Hi Matthew,

On Sun, Nov 4, 2018 at 2:06 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Sat, Nov 03, 2018 at 05:02:36AM -0700, Matthew Wilcox wrote:
> > On Sat, Nov 03, 2018 at 10:35:04AM +0530, Souptick Joarder wrote:
> > > Page fault handlers are supposed to return VM_FAULT codes,
> > > but some drivers/file systems mistakenly return error
> > > numbers. Now that all drivers/file systems have been converted
> > > to use the vm_fault_t return type, change the type definition
> > > to no longer be compatible with 'int'. By making it an unsigned
> > > int, the function prototype becomes incompatible with a function
> > > which returns int. Sparse will detect any attempts to return a
> > > value which is not a VM_FAULT code.
> >
> >
> > > -/* Encode hstate index for a hwpoisoned large page */
> > > -#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
> > > -#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
> > ...
> > > +/* Encode hstate index for a hwpoisoned large page */
> > > +#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
> > > +#define VM_FAULT_GET_HINDEX(x) (((x) >> 16) & 0xf)
> >
> > I think it's important to mention in the changelog that these values
> > have been changed to avoid conflicts with other VM_FAULT codes.
> >
> > > +/**
> > > + * typedef vm_fault_t -  __bitwise unsigned int
> > > + *
> > > + * vm_fault_t is the new unsigned int type to return VM_FAULT
> > > + * code by page fault handlers of drivers/file systems. Now if
> > > + * any page fault handlers returns non VM_FAULT code instead
> > > + * of VM_FAULT code, it will be a mismatch with function
> > > + * prototype and sparse will detect it.
> > > + */
> >
> > The first line should be what the typedef *means*, not repeat the
> > compiler's definition.  The rest of the description should be information
> > for someone coming to the type for the first time; what you've written
> > here is changelog material.
> >
> > /**
> >  * typedef vm_fault_t - Return type for page fault handlers.
> >  *
> >  * Page fault handlers return a bitmask of %VM_FAULT values.
> >  */
> >
> > > +typedef __bitwise unsigned int vm_fault_t;
> > > +
> > > +/**
> > > + * enum - VM_FAULT code
> >
> > Can you document an anonymous enum?  I've never tried.  Did you run this
> > through 'make htmldocs'?
>
> You cannot document an anonymous enum.


I assume, you are pointing to Document folder and I don't know if this
enum need to be documented or not.

I didn't run 'make htmldocs' as there is no document related changes.

>
> > > + * This enum is used to track the VM_FAULT code return by page
> > > + * fault handlers.
> >
> >  * Page fault handlers return a bitmask of these values to tell the
> >  * core VM what happened when handling the fault.
> >
>
> --
> Sincerely yours,
> Mike.
>

Re: [PATCH] mm: Create the new vm_fault_t type

[Mike Rapoport]

On Mon, Nov 05, 2018 at 11:14:17AM +0530, Souptick Joarder wrote:
> Hi Matthew,
> 
> On Sun, Nov 4, 2018 at 2:06 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
> >
> > On Sat, Nov 03, 2018 at 05:02:36AM -0700, Matthew Wilcox wrote:
> > > On Sat, Nov 03, 2018 at 10:35:04AM +0530, Souptick Joarder wrote:
> > > > Page fault handlers are supposed to return VM_FAULT codes,
> > > > but some drivers/file systems mistakenly return error
> > > > numbers. Now that all drivers/file systems have been converted
> > > > to use the vm_fault_t return type, change the type definition
> > > > to no longer be compatible with 'int'. By making it an unsigned
> > > > int, the function prototype becomes incompatible with a function
> > > > which returns int. Sparse will detect any attempts to return a
> > > > value which is not a VM_FAULT code.
> > >
> > >
> > > > -/* Encode hstate index for a hwpoisoned large page */
> > > > -#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
> > > > -#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
> > > ...
> > > > +/* Encode hstate index for a hwpoisoned large page */
> > > > +#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
> > > > +#define VM_FAULT_GET_HINDEX(x) (((x) >> 16) & 0xf)
> > >
> > > I think it's important to mention in the changelog that these values
> > > have been changed to avoid conflicts with other VM_FAULT codes.
> > >
> > > > +/**
> > > > + * typedef vm_fault_t -  __bitwise unsigned int
> > > > + *
> > > > + * vm_fault_t is the new unsigned int type to return VM_FAULT
> > > > + * code by page fault handlers of drivers/file systems. Now if
> > > > + * any page fault handlers returns non VM_FAULT code instead
> > > > + * of VM_FAULT code, it will be a mismatch with function
> > > > + * prototype and sparse will detect it.
> > > > + */
> > >
> > > The first line should be what the typedef *means*, not repeat the
> > > compiler's definition.  The rest of the description should be information
> > > for someone coming to the type for the first time; what you've written
> > > here is changelog material.
> > >
> > > /**
> > >  * typedef vm_fault_t - Return type for page fault handlers.
> > >  *
> > >  * Page fault handlers return a bitmask of %VM_FAULT values.
> > >  */
> > >
> > > > +typedef __bitwise unsigned int vm_fault_t;
> > > > +
> > > > +/**
> > > > + * enum - VM_FAULT code
> > >
> > > Can you document an anonymous enum?  I've never tried.  Did you run this
> > > through 'make htmldocs'?
> >
> > You cannot document an anonymous enum.
> 
> 
> I assume, you are pointing to Document folder and I don't know if this
> enum need to be documented or not.

The enum should be documented, even if it's documentation is (yet) not
linked anywhere in the Documentation/
 
> I didn't run 'make htmldocs' as there is no document related changes.

You can verify that kernel-doc can parse your documentation by running

scripts/kernel-doc -none -v <filename>

> >
> > > > + * This enum is used to track the VM_FAULT code return by page
> > > > + * fault handlers.
> > >
> > >  * Page fault handlers return a bitmask of these values to tell the
> > >  * core VM what happened when handling the fault.
> > >
> >
> > --
> > Sincerely yours,
> > Mike.
> >
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH] mm: Create the new vm_fault_t type

[Souptick Joarder]

On Mon, Nov 5, 2018 at 2:43 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Mon, Nov 05, 2018 at 11:14:17AM +0530, Souptick Joarder wrote:
> > Hi Matthew,
> >
> > On Sun, Nov 4, 2018 at 2:06 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
> > >
> > > On Sat, Nov 03, 2018 at 05:02:36AM -0700, Matthew Wilcox wrote:
> > > > On Sat, Nov 03, 2018 at 10:35:04AM +0530, Souptick Joarder wrote:
> > > > > Page fault handlers are supposed to return VM_FAULT codes,
> > > > > but some drivers/file systems mistakenly return error
> > > > > numbers. Now that all drivers/file systems have been converted
> > > > > to use the vm_fault_t return type, change the type definition
> > > > > to no longer be compatible with 'int'. By making it an unsigned
> > > > > int, the function prototype becomes incompatible with a function
> > > > > which returns int. Sparse will detect any attempts to return a
> > > > > value which is not a VM_FAULT code.
> > > >
> > > >
> > > > > -/* Encode hstate index for a hwpoisoned large page */
> > > > > -#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
> > > > > -#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
> > > > ...
> > > > > +/* Encode hstate index for a hwpoisoned large page */
> > > > > +#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
> > > > > +#define VM_FAULT_GET_HINDEX(x) (((x) >> 16) & 0xf)
> > > >
> > > > I think it's important to mention in the changelog that these values
> > > > have been changed to avoid conflicts with other VM_FAULT codes.
> > > >
> > > > > +/**
> > > > > + * typedef vm_fault_t -  __bitwise unsigned int
> > > > > + *
> > > > > + * vm_fault_t is the new unsigned int type to return VM_FAULT
> > > > > + * code by page fault handlers of drivers/file systems. Now if
> > > > > + * any page fault handlers returns non VM_FAULT code instead
> > > > > + * of VM_FAULT code, it will be a mismatch with function
> > > > > + * prototype and sparse will detect it.
> > > > > + */
> > > >
> > > > The first line should be what the typedef *means*, not repeat the
> > > > compiler's definition.  The rest of the description should be information
> > > > for someone coming to the type for the first time; what you've written
> > > > here is changelog material.
> > > >
> > > > /**
> > > >  * typedef vm_fault_t - Return type for page fault handlers.
> > > >  *
> > > >  * Page fault handlers return a bitmask of %VM_FAULT values.
> > > >  */
> > > >
> > > > > +typedef __bitwise unsigned int vm_fault_t;
> > > > > +
> > > > > +/**
> > > > > + * enum - VM_FAULT code
> > > >
> > > > Can you document an anonymous enum?  I've never tried.  Did you run this
> > > > through 'make htmldocs'?
> > >
> > > You cannot document an anonymous enum.
> >
> >
> > I assume, you are pointing to Document folder and I don't know if this
> > enum need to be documented or not.
>
> The enum should be documented, even if it's documentation is (yet) not
> linked anywhere in the Documentation/
>
> > I didn't run 'make htmldocs' as there is no document related changes.
>
> You can verify that kernel-doc can parse your documentation by running
>
> scripts/kernel-doc -none -v <filename>

I run "scripts/kernel-doc -none -v include/linux/mm_types.h" and it is showing
below error and warning which is linked to enum in discussion.

include/linux/mm_types.h:612: info: Scanning doc for typedef vm_fault_t
include/linux/mm_types.h:623: info: Scanning doc for enum
include/linux/mm_types.h:628: warning: contents before sections
include/linux/mm_types.h:660: error: Cannot parse enum!
1 errors
1 warnings

Shall I keep the documentation for enum or remove it from this patch ?

>
> > >
> > > > > + * This enum is used to track the VM_FAULT code return by page
> > > > > + * fault handlers.
> > > >
> > > >  * Page fault handlers return a bitmask of these values to tell the
> > > >  * core VM what happened when handling the fault.
> > > >
> > >
> > > --
> > > Sincerely yours,
> > > Mike.
> > >
> >
>
> --
> Sincerely yours,
> Mike.
>

Re: [PATCH] mm: Create the new vm_fault_t type

[Mike Rapoport]

On Mon, Nov 05, 2018 at 07:23:55PM +0530, Souptick Joarder wrote:
> On Mon, Nov 5, 2018 at 2:43 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
> >
> > On Mon, Nov 05, 2018 at 11:14:17AM +0530, Souptick Joarder wrote:
> > > Hi Matthew,
> > >
> > > On Sun, Nov 4, 2018 at 2:06 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
> > > >
> > > > On Sat, Nov 03, 2018 at 05:02:36AM -0700, Matthew Wilcox wrote:
> > > > > On Sat, Nov 03, 2018 at 10:35:04AM +0530, Souptick Joarder wrote:

> > > > > > +typedef __bitwise unsigned int vm_fault_t;
> > > > > > +
> > > > > > +/**
> > > > > > + * enum - VM_FAULT code
> > > > >
> > > > > Can you document an anonymous enum?  I've never tried.  Did you run this
> > > > > through 'make htmldocs'?
> > > >
> > > > You cannot document an anonymous enum.
> > >
> > > I assume, you are pointing to Document folder and I don't know if this
> > > enum need to be documented or not.
> >
> > The enum should be documented, even if it's documentation is (yet) not
> > linked anywhere in the Documentation/
> >
> > > I didn't run 'make htmldocs' as there is no document related changes.
> >
> > You can verify that kernel-doc can parse your documentation by running
> >
> > scripts/kernel-doc -none -v <filename>
> 
> I run "scripts/kernel-doc -none -v include/linux/mm_types.h" and it is showing
> below error and warning which is linked to enum in discussion.
> 
> include/linux/mm_types.h:612: info: Scanning doc for typedef vm_fault_t
> include/linux/mm_types.h:623: info: Scanning doc for enum
> include/linux/mm_types.h:628: warning: contents before sections
> include/linux/mm_types.h:660: error: Cannot parse enum!
> 1 errors
> 1 warnings
> 
> Shall I keep the documentation for enum or remove it from this patch ?

The documentation should be there, you just need to add a name for the
enum. Then kernel-doc will be able to parse it.
 
> > > >
> > > > > > + * This enum is used to track the VM_FAULT code return by page
> > > > > > + * fault handlers.
> > > > >

I think that the enum description should also include the text from the
comment that described VM_FAULT_* defines:

/*
 * Different kinds of faults, as returned by handle_mm_fault().
 * Used to decide whether a process gets delivered SIGBUS or
 * just gets major/minor fault counters bumped up.
 */



-- 
Sincerely yours,
Mike.

Re: [PATCH] mm: Create the new vm_fault_t type

[Souptick Joarder]

On Tue, Nov 6, 2018 at 11:51 AM Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Mon, Nov 05, 2018 at 07:23:55PM +0530, Souptick Joarder wrote:
> > On Mon, Nov 5, 2018 at 2:43 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
> > >
> > > On Mon, Nov 05, 2018 at 11:14:17AM +0530, Souptick Joarder wrote:
> > > > Hi Matthew,
> > > >
> > > > On Sun, Nov 4, 2018 at 2:06 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
> > > > >
> > > > > On Sat, Nov 03, 2018 at 05:02:36AM -0700, Matthew Wilcox wrote:
> > > > > > On Sat, Nov 03, 2018 at 10:35:04AM +0530, Souptick Joarder wrote:
>
> > > > > > > +typedef __bitwise unsigned int vm_fault_t;
> > > > > > > +
> > > > > > > +/**
> > > > > > > + * enum - VM_FAULT code
> > > > > >
> > > > > > Can you document an anonymous enum?  I've never tried.  Did you run this
> > > > > > through 'make htmldocs'?
> > > > >
> > > > > You cannot document an anonymous enum.
> > > >
> > > > I assume, you are pointing to Document folder and I don't know if this
> > > > enum need to be documented or not.
> > >
> > > The enum should be documented, even if it's documentation is (yet) not
> > > linked anywhere in the Documentation/
> > >
> > > > I didn't run 'make htmldocs' as there is no document related changes.
> > >
> > > You can verify that kernel-doc can parse your documentation by running
> > >
> > > scripts/kernel-doc -none -v <filename>
> >
> > I run "scripts/kernel-doc -none -v include/linux/mm_types.h" and it is showing
> > below error and warning which is linked to enum in discussion.
> >
> > include/linux/mm_types.h:612: info: Scanning doc for typedef vm_fault_t
> > include/linux/mm_types.h:623: info: Scanning doc for enum
> > include/linux/mm_types.h:628: warning: contents before sections
> > include/linux/mm_types.h:660: error: Cannot parse enum!
> > 1 errors
> > 1 warnings
> >
> > Shall I keep the documentation for enum or remove it from this patch ?
>
> The documentation should be there, you just need to add a name for the
> enum. Then kernel-doc will be able to parse it.
>
> > > > >
> > > > > > > + * This enum is used to track the VM_FAULT code return by page
> > > > > > > + * fault handlers.
> > > > > >
>
> I think that the enum description should also include the text from the
> comment that described VM_FAULT_* defines:
>
> /*
>  * Different kinds of faults, as returned by handle_mm_fault().
>  * Used to decide whether a process gets delivered SIGBUS or
>  * just gets major/minor fault counters bumped up.
>  */
>

Ok, will add  both in v2. Thanks.