Re: [RFC PATCH for 4.21 04/16] mm: Introduce vm_map_user_ram, vm_unmap_user_ram

[Steven Rostedt]

On Wed, 10 Oct 2018 15:19:24 -0400
Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:

> + * 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;

-- Steve