mm: introduce vma_is_anonymous(vma) helper

special_mapping_fault() is absolutely broken.  It seems it was always
wrong, but this didn't matter until vdso/vvar started to use more than
one page.

And after this change vma_is_anonymous() becomes really trivial, it
simply checks vm_ops == NULL.  However, I do think the helper makes
sense.  There are a lot of ->vm_ops != NULL checks, the helper makes the
caller's code more understandable (self-documented) and this is more
grep-friendly.

This patch (of 3):

Preparation.  Add the new simple helper, vma_is_anonymous(vma), and change
handle_pte_fault() to use it.  It will have more users.

The name is not accurate, say a hpet_mmap()'ed vma is not anonymous.
Perhaps it should be named vma_has_fault() instead.  But it matches the
logic in mmap.c/memory.c (see next changes).  "True" just means that a
page fault will use do_anonymous_page().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8b257c43855bbc32c04698a184055bb3be56bd80..dfb7ce05f1e3342eae69aa12fe4fdb31ac79d1ab 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1260,6 +1260,11 @@ static inline int vma_growsdown(struct vm_area_struct *vma, unsigned long addr)
        return vma && (vma->vm_end == addr) && (vma->vm_flags & VM_GROWSDOWN);
 }
 
+static inline bool vma_is_anonymous(struct vm_area_struct *vma)
+{
+       return !vma->vm_ops;
+}
+
 static inline int stack_guard_page_start(struct vm_area_struct *vma,
                                             unsigned long addr)
 {

diff --git a/mm/memory.c b/mm/memory.c
index bb04d8f2f86c415c24a52dadd71623a2316454d1..882c9d7ae2f5f9696e4ea416d919512b101382de 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3267,12 +3267,12 @@ static int handle_pte_fault(struct mm_struct *mm,
        barrier();
        if (!pte_present(entry)) {
                if (pte_none(entry)) {
-                       if (vma->vm_ops)
+                       if (vma_is_anonymous(vma))
+                               return do_anonymous_page(mm, vma, address,
+                                                        pte, pmd, flags);
+                       else
                                return do_fault(mm, vma, address, pte, pmd,
                                                flags, entry);
-
-                       return do_anonymous_page(mm, vma, address, pte, pmd,
-                                       flags);
                }
                return do_swap_page(mm, vma, address,
                                        pte, pmd, flags, entry);