Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 0b63d68..7907e64 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -64,7 +64,7 @@
 	else
 		bytes += kobjsize(current->files);
 
-	if (current->sighand && atomic_read(&current->sighand->count) > 1)
+	if (current->sighand && refcount_read(&current->sighand->count) > 1)
 		sbytes += kobjsize(current->sighand);
 	else
 		bytes += kobjsize(current->sighand);
@@ -178,7 +178,7 @@
 		seq_file_path(m, file, "");
 	} else if (mm && is_stack(vma)) {
 		seq_pad(m, ' ');
-		seq_printf(m, "[stack]");
+		seq_puts(m, "[stack]");
 	}
 
 	seq_putc(m, '\n');
@@ -211,7 +211,11 @@
 	if (!mm || !mmget_not_zero(mm))
 		return NULL;
 
-	down_read(&mm->mmap_sem);
+	if (down_read_killable(&mm->mmap_sem)) {
+		mmput(mm);
+		return ERR_PTR(-EINTR);
+	}
+
 	/* start from the Nth VMA */
 	for (p = rb_first(&mm->mm_rb); p; p = rb_next(p))
 		if (n-- == 0)