mm/rmap.c: don't reuse anon_vma if we just want a copy

Before commit 7a3ef208e662 ("mm: prevent endless growth of anon_vma
hierarchy"), anon_vma_clone() doesn't change dst->anon_vma.  While after
this commit, anon_vma_clone() will try to reuse an exist one on forking.

But this commit go a little bit further for the case not forking.
anon_vma_clone() is called from __vma_split(), __split_vma(), copy_vma()
and anon_vma_fork().  For the first three places, the purpose here is
get a copy of src and we don't expect to touch dst->anon_vma even it is
NULL.

While after that commit, it is possible to reuse an anon_vma when
dst->anon_vma is NULL.  This is not we intend to have.

This patch stops reuse of anon_vma for non-fork cases.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy")
Signed-off-by: Wei Yang <[email protected]>
Acked-by: Konstantin Khlebnikov <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: "Jérôme Glisse" <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Qian Cai <[email protected]>
Cc: Shakeel Butt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions