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Violators will be prosecuted for from ; Tue, 6 Nov 2018 09:01:02 -0000 Date: Tue, 6 Nov 2018 11:00:55 +0200 From: Mike Rapoport Subject: Re: [PATCH v2] mm: Create the new vm_fault_t type References: <20181106074934.GA27620@jordon-HP-15-Notebook-PC> <20181106082611.GB28505@rapoport-lnx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Message-Id: <20181106090054.GC28505@rapoport-lnx> Sender: owner-linux-mm@kvack.org List-ID: To: Souptick Joarder Cc: Matthew Wilcox , Andrew Morton , Michal Hocko , "Kirill A. Shutemov" , Dan Williams , vbabka@suse.cz, riel@redhat.com, Linux-MM , linux-kernel@vger.kernel.org On Tue, Nov 06, 2018 at 02:04:54PM +0530, Souptick Joarder wrote: > On Tue, Nov 6, 2018 at 1:56 PM Mike Rapoport 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 > > > --- > > > 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.