Merge branch 'akpm' (patches from Andrew)

Merge misc VM fixes from Andrew Morton:
 "A bunch of hotfixes, all affecting mm/.

  The two-patch series from Andrea may be controversial. This restores
  patches which were reverted in Dec 2018 due to a regression report [*].

  After extensive discussion it is evident that the problems which these
  patches solved were significantly more serious than the problems they
  introduced. I am told that major distros are already carrying these
  two patches for this reason"

[*] See

      https://lore.kernel.org/lkml/alpine.DEB.2.21.1812061343240.144733@chino.kir.corp.google.com/
      https://lore.kernel.org/lkml/alpine.DEB.2.21.1812031545560.161134@chino.kir.corp.google.com/

  for the google-specific issues brought up by David Rijentes. And as
  Andrew says:

    "I'm unaware of anyone else who will be adversely affected by this,
     and google already carries over a thousand kernel patches - another
     won't kill them.

     There has been sporadic discussion about fixing these things for
     real but it's clear that nobody apart from David is particularly
     motivated"

* emailed patches from Andrew Morton <akpm@linux-foundation.org>:
  hugetlbfs: fix hugetlb page migration/fault race causing SIGBUS
  mm, vmscan: do not special-case slab reclaim when watermarks are boosted
  Revert "mm, thp: restore node-local hugepage allocations"
  Revert "Revert "mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask""
  include/asm-generic/5level-fixup.h: fix variable 'p4d' set but not used
  seq_file: fix problem when seeking mid-record
  mm: workingset: fix vmstat counters for shadow nodes
  mm/usercopy: use memory range to be accessed for wraparound check
  mm: kmemleak: disable early logging in case of error
  mm/vmalloc.c: fix percpu free VM area search criteria
  mm/memcontrol.c: fix use after free in mem_cgroup_iter()
  mm/z3fold.c: fix z3fold_destroy_pool() race condition
  mm/z3fold.c: fix z3fold_destroy_pool() ordering
  mm: mempolicy: handle vma with unmovable pages mapped correctly in mbind
  mm: mempolicy: make the behavior consistent when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified
  mm/hmm: fix bad subpage pointer in try_to_unmap_one
  mm/hmm: fix ZONE_DEVICE anon page mapping reuse
  mm: document zone device struct page field usage

1 files changed, 19 insertions, 0 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ede7e7f5d1ab..6d7296dd11b8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3856,6 +3856,25 @@ retry:
 
 		page = alloc_huge_page(vma, haddr, 0);
 		if (IS_ERR(page)) {
+			/*
+			 * Returning error will result in faulting task being
+			 * sent SIGBUS.  The hugetlb fault mutex prevents two
+			 * tasks from racing to fault in the same page which
+			 * could result in false unable to allocate errors.
+			 * Page migration does not take the fault mutex, but
+			 * does a clear then write of pte's under page table
+			 * lock.  Page fault code could race with migration,
+			 * notice the clear pte and try to allocate a page
+			 * here.  Before returning error, get ptl and make
+			 * sure there really is no pte entry.
+			 */
+			ptl = huge_pte_lock(h, mm, ptep);
+			if (!huge_pte_none(huge_ptep_get(ptep))) {
+				ret = 0;
+				spin_unlock(ptl);
+				goto out;
+			}
+			spin_unlock(ptl);
 			ret = vmf_error(PTR_ERR(page));
 			goto out;
 		}