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

From: Mike Rapoport
Date: Tue Nov 06 2018 - 04:01:08 EST

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On Tue, Nov 06, 2018 at 02:04:54PM +0530, Souptick Joarder wrote:
> 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 ?
> >

The description below is fine, but kernel-doc will use "VM_FAULT code" as
the "short description" and the explanation will be used as "long
description".

So either replace "VM_FAULT code" with something like "page fault handler
return codes" or put the long explanation next to 'enum vm_fault_reason':

/**
* enum vm_fault_reason - page fault handlers return a bitmask of these
* values ...
* ...
*/

Please take a look at "Structure, union, and enumeration documentation" in
Documentation/doc-guide/kernel-doc.rst [1].

[1] https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html#structure-union-and-enumeration-documentation

> > > + *
> > > + * 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.
> >
>

--
Sincerely yours,
Mike.

Next message: Alexey Budankov: "[PATCH v15 1/3]: perf util: map data buffer for preserving collected data"
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In reply to: Souptick Joarder: "Re: [PATCH v2] mm: Create the new vm_fault_t type"
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