Merge branch 'akpm' (patches from Andrew)

Merge misc fixes from Andrew Morton:
 "15 fixes"

[ This does not merge the "fortify: use WARN instead of BUG for now"
  patch, which needs a bit of extra work to build cleanly with all
  configurations. Arnd is on it.   - Linus ]

* emailed patches from Andrew Morton <akpm@linux-foundation.org>:
  ocfs2: don't clear SGID when inheriting ACLs
  mm: allow page_cache_get_speculative in interrupt context
  userfaultfd: non-cooperative: flush event_wqh at release time
  ipc: add missing container_of()s for randstruct
  cpuset: fix a deadlock due to incomplete patching of cpusets_enabled()
  userfaultfd_zeropage: return -ENOSPC in case mm has gone
  mm: take memory hotplug lock within numa_zonelist_order_handler()
  mm/page_io.c: fix oops during block io poll in swapin path
  zram: do not free pool->size_class
  kthread: fix documentation build warning
  kasan: avoid -Wmaybe-uninitialized warning
  userfaultfd: non-cooperative: notify about unmap of destination during mremap
  mm, mprotect: flush TLB if potentially racing with a parallel reclaim leaving stale TLB entries
  pid: kill pidhash_size in pidhash_init()
  mm/hugetlb.c: __get_user_pages ignores certain follow_hugetlb_page errors

1 files changed, 36 insertions, 0 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index ced14f1af6dc..c8993c63eb25 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -605,6 +605,13 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
 	tlb_ubc->flush_required = true;
 
 	/*
+	 * Ensure compiler does not re-order the setting of tlb_flush_batched
+	 * before the PTE is cleared.
+	 */
+	barrier();
+	mm->tlb_flush_batched = true;
+
+	/*
 	 * If the PTE was dirty then it's best to assume it's writable. The
 	 * caller must use try_to_unmap_flush_dirty() or try_to_unmap_flush()
 	 * before the page is queued for IO.
@@ -631,6 +638,35 @@ static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
 
 	return should_defer;
 }
+
+/*
+ * Reclaim unmaps pages under the PTL but do not flush the TLB prior to
+ * releasing the PTL if TLB flushes are batched. It's possible for a parallel
+ * operation such as mprotect or munmap to race between reclaim unmapping
+ * the page and flushing the page. If this race occurs, it potentially allows
+ * access to data via a stale TLB entry. Tracking all mm's that have TLB
+ * batching in flight would be expensive during reclaim so instead track
+ * whether TLB batching occurred in the past and if so then do a flush here
+ * if required. This will cost one additional flush per reclaim cycle paid
+ * by the first operation at risk such as mprotect and mumap.
+ *
+ * This must be called under the PTL so that an access to tlb_flush_batched
+ * that is potentially a "reclaim vs mprotect/munmap/etc" race will synchronise
+ * via the PTL.
+ */
+void flush_tlb_batched_pending(struct mm_struct *mm)
+{
+	if (mm->tlb_flush_batched) {
+		flush_tlb_mm(mm);
+
+		/*
+		 * Do not allow the compiler to re-order the clearing of
+		 * tlb_flush_batched before the tlb is flushed.
+		 */
+		barrier();
+		mm->tlb_flush_batched = false;
+	}
+}
 #else
 static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
 {