Merge branch 'akpm' (incoming from Andrew Morton)

Merge fixes from Andrew Morton:
 "A bunch of fixes and one simple fbdev driver which missed the merge
  window because people will still talking about it (to no great
  effect)."

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (30 commits)
  aio: fix kioctx not being freed after cancellation at exit time
  mm/pagewalk.c: walk_page_range should avoid VM_PFNMAP areas
  drivers/rtc/rtc-max8998.c: check for pdata presence before dereferencing
  ocfs2: goto out_unlock if ocfs2_get_clusters_nocache() failed in ocfs2_fiemap()
  random: fix accounting race condition with lockless irq entropy_count update
  drivers/char/random.c: fix priming of last_data
  mm/memory_hotplug.c: fix printk format warnings
  nilfs2: fix issue of nilfs_set_page_dirty() for page at EOF boundary
  drivers/block/brd.c: fix brd_lookup_page() race
  fbdev: FB_GOLDFISH should depend on HAS_DMA
  drivers/rtc/rtc-pl031.c: pass correct pointer to free_irq()
  auditfilter.c: fix kernel-doc warnings
  aio: fix io_getevents documentation
  revert "selftest: add simple test for soft-dirty bit"
  drivers/leds/leds-ot200.c: fix error caused by shifted mask
  mm/THP: use pmd_populate() to update the pmd with pgtable_t pointer
  linux/kernel.h: fix kernel-doc warning
  mm compaction: fix of improper cache flush in migration code
  rapidio/tsi721: fix bug in MSI interrupt handling
  hfs: avoid crash in hfs_bnode_create
  ...

1 files changed, 12 insertions, 2 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index cb1c9dedf9b6..010d6c14129a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4108,8 +4108,6 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
 	if (mem_cgroup_disabled())
 		return NULL;
 
-	VM_BUG_ON(PageSwapCache(page));
-
 	if (PageTransHuge(page)) {
 		nr_pages <<= compound_order(page);
 		VM_BUG_ON(!PageTransHuge(page));
@@ -4205,6 +4203,18 @@ void mem_cgroup_uncharge_page(struct page *page)
 	if (page_mapped(page))
 		return;
 	VM_BUG_ON(page->mapping && !PageAnon(page));
+	/*
+	 * If the page is in swap cache, uncharge should be deferred
+	 * to the swap path, which also properly accounts swap usage
+	 * and handles memcg lifetime.
+	 *
+	 * Note that this check is not stable and reclaim may add the
+	 * page to swap cache at any time after this.  However, if the
+	 * page is not in swap cache by the time page->mapcount hits
+	 * 0, there won't be any page table references to the swap
+	 * slot, and reclaim will free it and not actually write the
+	 * page to disk.
+	 */
 	if (PageSwapCache(page))
 		return;
 	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_ANON, false);