Re: [PATCH v2] mm: Create the new vm_fault_t type

[Souptick Joarder]

On Tue, Nov 6, 2018 at 1:56 PM Mike Rapoport <rppt@xxxxxxxxxxxxx> wrote:
>
> On Tue, Nov 06, 2018 at 01:19:34PM +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.
> >
> > VM_FAULT_SET_HINDEX and VM_FAULT_GET_HINDEX values are changed
> > to avoid conflict with other VM_FAULT codes.
> >
> > Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> > ---
> > v2: Updated the change log and corrected the document part.
> >     name added to the enum that kernel-doc able to parse it.
> >
> >  include/linux/mm.h       | 46 ------------------------------
> >  include/linux/mm_types.h | 73 +++++++++++++++++++++++++++++++++++++++++++++++-
> >  2 files changed, 72 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..beee607 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 +608,78 @@ static inline bool mm_tlb_flush_nested(struct mm_struct *mm)
> >
> >  struct vm_fault;
> >
> > +/**
> > + * 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
>
> It should be 'enum vm_fault_reason' here.

Sorry, missed it.

> A more elaborate brief description would also be nice.

This much description is not sufficient to explain the enum ?
>
> > + *
> > + * Page fault handlers return a bitmask of these values to tell
> > + * the core VM what happened when handling the fault. Used to decide
> > + * whether a process gets delivered SIGBUS or just gets major/minor
> > + * fault counters bumped up.
> > + *
> > + * @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_reason {
> > +     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
> >
>
> --
> Sincerely yours,
> Mike.
>