mm: mprotect: use pmd_trans_unstable instead of taking the pmd_lock
authorAndrea Arcangeli <aarcange@redhat.com>
Wed, 22 Feb 2017 23:44:12 +0000 (15:44 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 23 Feb 2017 00:41:29 +0000 (16:41 -0800)
commit175ad4f1e7a29c8f914254e2e6316c50671e027a
treeecc4847e73314b2cc2db78f6a24e2f9e78b47905
parent7a0c4cf85b856430af62a907dd65dfc51438d24f
mm: mprotect: use pmd_trans_unstable instead of taking the pmd_lock

pmd_trans_unstable does an atomic read on the pmd so it doesn't require
the pmd_lock for the same check.

This also removes the special assumption that the mmap_sem is hold for
writing if prot_numa is not set.  userfaultfd will hold the mmap_sem
only for reading in change_pte_range like prot_numa, but it will not set
prot_numa.

This is always a valid micro-optimization regardless of userfaultfd.

[kirill@shutemov.name: drop unneeded pmd_trans_unstable(pmd) check after __split_huge_pmd()]
Link: http://lkml.kernel.org/r/20170208120421.GE5578@node.shutemov.name
Link: http://lkml.kernel.org/r/20161216144821.5183-43-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/mprotect.c