Merge branch 'akpm' (patches from Andrew)

Merge fixes from Andrew Morton:
 "26 fixes"

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (26 commits)
  MAINTAINERS: add Dan Streetman to zbud maintainers
  MAINTAINERS: add Dan Streetman to zswap maintainers
  mm: do not export ioremap_page_range symbol for external module
  mn10300: fix build error of missing fpu_save()
  romfs: use different way to generate fsid for BLOCK or MTD
  frv: add missing atomic64 operations
  mm, page_alloc: fix premature OOM when racing with cpuset mems update
  mm, page_alloc: move cpuset seqcount checking to slowpath
  mm, page_alloc: fix fast-path race with cpuset update or removal
  mm, page_alloc: fix check for NULL preferred_zone
  kernel/panic.c: add missing \n
  fbdev: color map copying bounds checking
  frv: add atomic64_add_unless()
  mm/mempolicy.c: do not put mempolicy before using its nodemask
  radix-tree: fix private list warnings
  Documentation/filesystems/proc.txt: add VmPin
  mm, memcg: do not retry precharge charges
  proc: add a schedule point in proc_pid_readdir()
  mm: alloc_contig: re-allow CMA to compact FS pages
  mm/slub.c: trace free objects at KERN_INFO
  ...

1 files changed, 17 insertions, 1 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9a6bd6c8d55a..5f3ad65c85de 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -783,6 +783,12 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 
 	assert_spin_locked(pmd_lockptr(mm, pmd));
 
+	/*
+	 * When we COW a devmap PMD entry, we split it into PTEs, so we should
+	 * not be in this function with `flags & FOLL_COW` set.
+	 */
+	WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
+
 	if (flags & FOLL_WRITE && !pmd_write(*pmd))
 		return NULL;
 
@@ -1128,6 +1134,16 @@ out_unlock:
 	return ret;
 }
 
+/*
+ * FOLL_FORCE can write to even unwritable pmd's, but only
+ * after we've gone through a COW cycle and they are dirty.
+ */
+static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
+{
+	return pmd_write(pmd) ||
+	       ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
+}
+
 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 				   unsigned long addr,
 				   pmd_t *pmd,
@@ -1138,7 +1154,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 
 	assert_spin_locked(pmd_lockptr(mm, pmd));
 
-	if (flags & FOLL_WRITE && !pmd_write(*pmd))
+	if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
 		goto out;
 
 	/* Avoid dumping huge zero page */