Re: BUG_ON() vs ASSERT()

["Mihai Donțu" <mihai.dontu@gmail.com>]

On Tue, 13 Sep 2016 09:10:32 -0400 Konrad Rzeszutek Wilk wrote:
> On Mon, Sep 12, 2016 at 09:23:41AM -0600, Jan Beulich wrote:
> > All,
> > 
> > in
> > https://lists.xenproject.org/archives/html/xen-devel/2016-09/msg01201.html
> > and
> > https://lists.xenproject.org/archives/html/xen-devel/2016-09/msg01210.html
> > Andrew basically suggests that we should switch away from using
> > ASSERT() and over to BUG_ON() in perhaps quite broad a set of
> > cases. And honestly I'm not convinced of this: We've been adding
> > quite a few ASSERT()s over the last years with the aim of doing
> > sanity checking in debug builds, without adding overhead to non-
> > debug builds. I can certainly see possible cases where using
> > BUG_ON() to prevent further possible damage is appropriate, but
> > I don't think we should overdo here.
> > 
> > Thanks for other's opinions,  
> 
> I am in the mindset that ASSERTS are in the cases where a check
> has been done earlier and the ASSERT is more of a catch if we ended up
> somehow in the wrong state. We can then slowly follow the breadcrumbs to
> see what changed the state. In other words - something that the hypervisor
> has checked for and that invariant should have not changed.
> 
> But a BUG_ON is in the same category - it should not have happend.
> 
> Perhaps the distinction is that for ASSERTS() it is to catch me messing
> things up. While BUG_ON() is something (or somebody) else messing things up.
> 
> It is kind of hard to describe the semantic of an ASSERT vs BUG_ON now
> that I think of it ..

I would see ASSERT() used to check for conditions that have immediate
and visible consequences, like the ones that lead to lack of
functionality (like a hw feature misdetection) or straight crashes
(like NULL-dereference). BUG_ON(), on the other hand, would be an early
warning for subtle corruptions that can lead to a hypervisor crash or
corrupted data after many hours of use (close to impossible to track
down).

For example, a while ago I posted a small patch that would BUG_ON()
when it detected that the heap chunks were not properly linked. That's
the type of bug that's a pain to detect.

-- 
Mihai Donțu

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