On Wed, Oct 24, 2018 at 12:35:03AM +0300, Igor Stoppa wrote:

+static __always_inline
+bool __pratomic_long_op(bool inc, struct pratomic_long_t *l)
+{
+	struct page *page;
+	uintptr_t base;
+	uintptr_t offset;
+	unsigned long flags;
+	size_t size = sizeof(*l);
+	bool is_virt = __is_wr_after_init(l, size);
+
+	if (WARN(!(is_virt || likely(__is_wr_pool(l, size))),
+		 WR_ERR_RANGE_MSG))
+		return false;
+	local_irq_save(flags);
+	if (is_virt)
+		page = virt_to_page(l);
+	else
+		vmalloc_to_page(l);
+	offset = (~PAGE_MASK) & (uintptr_t)l;
+	base = (uintptr_t)vmap(&page, 1, VM_MAP, PAGE_KERNEL);
+	if (WARN(!base, WR_ERR_PAGE_MSG)) {
+		local_irq_restore(flags);
+		return false;
+	}
+	if (inc)
+		atomic_long_inc((atomic_long_t *)(base + offset));
+	else
+		atomic_long_dec((atomic_long_t *)(base + offset));
+	vunmap((void *)base);
+	local_irq_restore(flags);
+	return true;
+
+}

That's just hideously nasty.. and horribly broken.

We're not going to duplicate all these kernel interfaces wrapped in gunk
like that. Also, you _cannot_ call vunmap() with IRQs disabled. Clearly
you've never tested this with debug bits enabled.