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Date: Sat, 3 Nov 2018 10:41:09 +0530
From: Souptick Joarder <jrdr.linux@...il.com>
To: Matthew Wilcox <willy@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...e.com>,
Dan Williams <dan.j.williams@...el.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
pasha.tatashin@...cle.com, vbabka@...e.cz, riel@...hat.com
Cc: Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Create the new vm_fault_t type
On Sat, Nov 3, 2018 at 10:31 AM Souptick Joarder <jrdr.linux@...il.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@...il.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
>
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