mm, hugetlb: abort __get_user_pages if current has been oom killed

If __get_user_pages() is faulting a significant number of hugetlb pages,
usually as the result of mmap(MAP_LOCKED), it can potentially allocate a
very large amount of memory.

If the process has been oom killed, this will cause a lot of memory to
potentially deplete memory reserves.

In the same way that commit 4779280 ("mm: make get_user_pages()
interruptible") aborted for pending SIGKILLs when faulting non-hugetlb
memory, based on the premise of commit 462e00c ("oom: stop
allocating user memory if TIF_MEMDIE is set"), hugetlb page faults now
terminate when the process has been oom killed.

Signed-off-by: David Rientjes <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Acked-by: Greg Thelen <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Acked-by: "Kirill A. Shutemov" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/hugetlb.c

@@ -3277,6 +3277,15 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		int absent;
 		struct page *page;
 
+		/*
+		 * If we have a pending SIGKILL, don't keep faulting pages and
+		 * potentially allocating memory.
+		 */
+		if (unlikely(fatal_signal_pending(current))) {
+			remainder = 0;
+			break;
+		}
+
 		/*
 		 * Some archs (sparc64, sh*) have multiple pte_ts to
 		 * each hugepage.  We have to make sure we get the