----- On Oct 16, 2018, at 2:30 PM, rostedt rostedt@goodmis.org wrote:

On Wed, 10 Oct 2018 15:19:24 -0400
Mathieu Desnoyers [off-list ref] wrote:

quoted

+ * vm_unmap_user_ram - unmap linear kernel address space set up by
vm_map_user_ram
+ * @mem: the pointer returned by vm_map_user_ram
+ * @count: the count passed to that vm_map_user_ram call (cannot unmap partial)
+ */
+void vm_unmap_user_ram(const void *mem, unsigned int count)
+{
+	unsigned long size = (unsigned long)count << PAGE_SHIFT;
+	unsigned long addr = (unsigned long)mem;
+	struct vmap_area *va;
+
+	might_sleep();
+	BUG_ON(!addr);
+	BUG_ON(addr < VMALLOC_START);
+	BUG_ON(addr > VMALLOC_END);
+	BUG_ON(!PAGE_ALIGNED(addr));
+
+	debug_check_no_locks_freed(mem, size);
+	va = find_vmap_area(addr);
+	BUG_ON(!va);
+	free_unmap_vmap_area(va);
+}
+EXPORT_SYMBOL(vm_unmap_user_ram);
+

Noticing this from Sergey's question in another patch, why are you
using BUG_ON()? That's rather extreme and something we are trying to
avoid adding more of (I still need to remove the BUG_ON()s I've added
over ten years ago). I don't see why all these BUG_ON's can't be turned
into:

if (WARN_ON(x))
	return;

I borrowed the code from vm_unmap_ram(), which has the following checks:

        BUG_ON(!addr);
        BUG_ON(addr < VMALLOC_START);
        BUG_ON(addr > VMALLOC_END);
        BUG_ON(!PAGE_ALIGNED(addr));
[...]
        va = find_vmap_area(addr);
        BUG_ON(!va);

The expectation here is that inputs to vm_unmap_ram() should always come from
vm_map_ram(), so an erroneous input is an internal kernel bug. I applied the
same logic to vm_unmap_user_ram() and vm_map_user_ram().

Should we turn all those BUG_ON() into if (WARN_ON(x)) return; in vm_{map,unmap}_ram
as well ?

Thanks,

Mathieu

-- Steve

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com