On Fri, 15 Apr 2022 14:11:32 -0600 Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > > > I grabbed > > https://kojipkgs.fedoraproject.org//packages/kernel/5.18.0/0.rc2.23.fc37/src/kernel-5.18.0-0.rc2.23.fc37.src.rpm > > and > > Yes, Fedora/RHEL is one concrete example of the model I mentioned > above (experimental/stable). I added Justin, the Fedora kernel > maintainer, and he can further clarify. > > If we don't want more VM_BUG_ONs, I'll remove them. But (let me > reiterate) it seems to me that just defeats the purpose of having > CONFIG_DEBUG_VM. > Well, I feel your pain. It was never expected that VM_BUG_ON() would get subverted in this fashion. We could create a new MM-developer-only assertion. Might even call it MM_BUG_ON(). With compile-time enablement but perhaps not a runtime switch. With nice simple semantics, please. Like "it returns void" and "if you pass an expression with side-effects then you lose". And "if you send a patch which produces warnings when CONFIG_MM_BUG_ON=n then you get to switch to windows95 for a month". Let's leave the mglru assertions in place for now and let's think about creating something more suitable, with a view to switching mglru over to that at a later time. But really, none of this addresses the core problem: *_BUG_ON() often kills the kernel. So guess what we just did? We killed the user's kernel at the exact time when we least wished to do so: when they have a bug to report to us. So the thing is self-defeating. It's much much better to WARN and to attempt to continue. This makes it much more likely that we'll get to hear about the kernel flaw.
