hugetlb: fix nr_pmds accounting with shared page tables
authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fri, 24 Jun 2016 21:49:51 +0000 (14:49 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Sat, 25 Jun 2016 00:23:52 +0000 (17:23 -0700)
commitc17b1f42594eb71b8d3eb5a6dfc907a7eb88a51d
treeb24f8fa0aaa1537ea9965e22ca6b9c9a030d2be5
parent06d8fbc7cfd655d202cfac9870bd79c18c2db698
hugetlb: fix nr_pmds accounting with shared page tables

We account HugeTLB's shared page table to all processes who share it.
The accounting happens during huge_pmd_share().

If somebody populates pud entry under us, we should decrease pagetable's
refcount and decrease nr_pmds of the process.

By mistake, I increase nr_pmds again in this case.  :-/ It will lead to
"BUG: non-zero nr_pmds on freeing mm: 2" on process' exit.

Let's fix this by increasing nr_pmds only when we're sure that the page
table will be used.

Link: http://lkml.kernel.org/r/20160617122506.GC6534@node.shutemov.name
Fixes: dc6c9a35b66b ("mm: account pmd page tables to the process")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: zhongjiang <zhongjiang@huawei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/hugetlb.c