mremap: don't do uneccesary checks if new_len == old_len

The "new_len > old_len" branch in vma_to_resize() looks very confusing.
It only covers the VM_DONTEXPAND/pgoff checks but everything below is
equally unneeded if new_len == old_len.

Change this code to return if "new_len == old_len", new_len < old_len is
not possible, otherwise the code below is wrong anyway.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Laurent Dufour <ldufour@linux.vnet.ibm.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/mm/mremap.c b/mm/mremap.c
index 7dcf7b42068e66f59a2c4444c4a39c8851ee186e..d3f42bece564384d5eb07af0f6a2657088fa80a1 100644 (file)
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -346,6 +346,7 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
 {
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma = find_vma(mm, addr);
+       unsigned long pgoff;
 
        if (!vma || vma->vm_start > addr)
                return ERR_PTR(-EFAULT);
@@ -357,17 +358,17 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
        if (old_len > vma->vm_end - addr)
                return ERR_PTR(-EFAULT);
 
+       if (new_len == old_len)
+               return vma;
+
        /* Need to be careful about a growing mapping */
-       if (new_len > old_len) {
-               unsigned long pgoff;
-
-               if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
-                       return ERR_PTR(-EFAULT);
-               pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
-               pgoff += vma->vm_pgoff;
-               if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
-                       return ERR_PTR(-EINVAL);
-       }
+       pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
+       pgoff += vma->vm_pgoff;
+       if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
+               return ERR_PTR(-EINVAL);
+
+       if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
+               return ERR_PTR(-EFAULT);
 
        if (vma->vm_flags & VM_LOCKED) {
                unsigned long locked, lock_limit;