Merge branch 'akpm' (patches from Andrew)

Merge misc fixes from Andrew Morton:
 "28 patches.

  Subsystems affected by this series: mm (memblock, pagealloc, hugetlb,
  highmem, kfence, oom-kill, madvise, kasan, userfaultfd, memcg, and
  zram), core-kernel, kconfig, fork, binfmt, MAINTAINERS, kbuild, and
  ia64"

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (28 commits)
  zram: fix broken page writeback
  zram: fix return value on writeback_store
  mm/memcg: set memcg when splitting page
  mm/memcg: rename mem_cgroup_split_huge_fixup to split_page_memcg and add nr_pages argument
  ia64: fix ptrace(PTRACE_SYSCALL_INFO_EXIT) sign
  ia64: fix ia64_syscall_get_set_arguments() for break-based syscalls
  mm/userfaultfd: fix memory corruption due to writeprotect
  kasan: fix KASAN_STACK dependency for HW_TAGS
  kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC
  mm/madvise: replace ptrace attach requirement for process_madvise
  include/linux/sched/mm.h: use rcu_dereference in in_vfork()
  kfence: fix reports if constant function prefixes exist
  kfence, slab: fix cache_alloc_debugcheck_after() for bulk allocations
  kfence: fix printk format for ptrdiff_t
  linux/compiler-clang.h: define HAVE_BUILTIN_BSWAP*
  MAINTAINERS: exclude uapi directories in API/ABI section
  binfmt_misc: fix possible deadlock in bm_register_write
  mm/highmem.c: fix zero_user_segments() with start > end
  hugetlb: do early cow when page pinned on src mm
  mm: use is_cow_mapping() across tree where proper
  ...

1 files changed, 12 insertions, 5 deletions

diff --git a/mm/highmem.c b/mm/highmem.c
index 874b732b120c..86f2b9495f9c 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -368,20 +368,24 @@ void zero_user_segments(struct page *page, unsigned start1, unsigned end1,
 
 	BUG_ON(end1 > page_size(page) || end2 > page_size(page));
 
+	if (start1 >= end1)
+		start1 = end1 = 0;
+	if (start2 >= end2)
+		start2 = end2 = 0;
+
 	for (i = 0; i < compound_nr(page); i++) {
 		void *kaddr = NULL;
 
-		if (start1 < PAGE_SIZE || start2 < PAGE_SIZE)
-			kaddr = kmap_atomic(page + i);
-
 		if (start1 >= PAGE_SIZE) {
 			start1 -= PAGE_SIZE;
 			end1 -= PAGE_SIZE;
 		} else {
 			unsigned this_end = min_t(unsigned, end1, PAGE_SIZE);
 
-			if (end1 > start1)
+			if (end1 > start1) {
+				kaddr = kmap_atomic(page + i);
 				memset(kaddr + start1, 0, this_end - start1);
+			}
 			end1 -= this_end;
 			start1 = 0;
 		}
@@ -392,8 +396,11 @@ void zero_user_segments(struct page *page, unsigned start1, unsigned end1,
 		} else {
 			unsigned this_end = min_t(unsigned, end2, PAGE_SIZE);
 
-			if (end2 > start2)
+			if (end2 > start2) {
+				if (!kaddr)
+					kaddr = kmap_atomic(page + i);
 				memset(kaddr + start2, 0, this_end - start2);
+			}
 			end2 -= this_end;
 			start2 = 0;
 		}