Re: [PATCH] mm: Use BUG_ON instead of if condition followed by BUG

[John Hubbard]

On 11/24/21 19:32, Matthew Wilcox wrote:
> On Wed, Nov 24, 2021 at 02:45:59PM -0800, John Hubbard wrote:
> > @@ -2201,13 +2201,12 @@ static int __ref try_remove_memory(u64 start, u64 size)
> > */
> > void __remove_memory(u64 start, u64 size)
> > {
> > -
> > +       int ret = try_remove_memory(start, size);
> > /*
> > * trigger BUG() if some memory is not offlined prior to calling this
> > * function
> > */
> > -       if (try_remove_memory(start, size))
> > -               BUG();
> > +       BUG_ON(ret);
> > }
>
> I'd rather leave it the way it is.  I don't see why the version you
> propose is better.


In isolation, it's *not* better. It's only potentially useful in the
context of "code plus tools". That is to say, if the coccinelle change
request were rejected, then this provides a way forward that is not
worse than the existing code, and also works around the warning.


> > ...and by the way, while going to type that, I immediately stumbled upon
> > another pre-existing case of this sort of thing, in try_remove_memory(),
> > which does this:
> >
> > static int __ref try_remove_memory(u64 start, u64 size)
> > {
> > 	struct vmem_altmap mhp_altmap = {};
> > 	struct vmem_altmap *altmap = NULL;
> > 	unsigned long nr_vmemmap_pages;
> > 	int rc = 0, nid = NUMA_NO_NODE;
> >
> > 	BUG_ON(check_hotplug_memory_range(start, size));
>
> That needs to be fixed.


Yes it does. :) I pointed it out in hopes that Chiminghao might be inspired
to go find and fix some of these.


thanks,
--
John Hubbard
NVIDIA