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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>
This commit is contained in:
Oleg Nesterov 2015-09-04 15:48:10 -07:00 committed by Linus Torvalds
parent d456fb9e52
commit 1d39168697
1 changed files with 11 additions and 10 deletions
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21
mm/mremap.c
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@ -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);
/* Need to be careful about a growing mapping */
if (new_len > old_len) {
unsigned long pgoff;
if (new_len == old_len)
return vma;
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);
}
/* Need to be careful about a growing mapping */
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;