Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH] mm/page_isolation: don't putback unisolated page | Date | Thu, 9 Sep 2021 11:37:26 +0200 |
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On 09.09.21 11:07, Vlastimil Babka wrote: > On 9/9/21 10:56, David Hildenbrand wrote: >> On 09.09.21 00:42, John Hubbard wrote: >>> On 9/7/21 2:56 AM, David Hildenbrand wrote: >>> ... >>>>> If this can be handled gracefully, then I'd rather go with VM_WARN_ON. >>>>> Maybe even WARN_ON_ONCE? >>>>> >>>> >>>> I think either VM_BUG_ON() or VM_WARN_ON() -- compiling the runtime >>>> checks out -- should be good >>>> enough. >>>> >>>> I'd just go with VM_BUG_ON(), because anybody messing with >>>> __isolate_free_page() should clearly spot >>>> that we expect the current handling. But no strong opinion. >>>> >>> >>> If in doubt, WARN*() should be preferred over BUG*(). There's a pretty long >>> history of "don't kill the machine unless you have to" emails about this, let >>> me dig up one...OK, maybe not the best example, but the tip of the iceberg: >> >> Please note the subtle difference between BUG_ON and VM_BUG_ON. We expect >> VM_BUG_ON to be compiled out on any production system. So it's really only a >> mean to identify things that really shouldn't be like that during >> debugging/testing. > > IIRC Fedora used to have CONFIG_DEBUG_VM enabled, did it change?
Excellent question. Apparently you are right. Fortunately it's not a distro to use in production ;)
In kernel-ark:
redhat/configs/fedora/generic/CONFIG_DEBUG_VM:CONFIG_DEBUG_VM=y
While for ARK (rhel-next so to say)
redhat/configs/ark/generic/CONFIG_DEBUG_VM:# CONFIG_DEBUG_VM is not set
So yes, the VM_WARN_ON would then be preferred in that case. But it's something that should never ever happen unless reviewers and developers really mess up, so I don't actually would sleep over that. We have other WARN... that can trigger more easily.
> >> Using WARN... instead of VM_BUG_ON is even worse for production systems. >> There are distros that set panic_on_warn, essentially converting WARN... >> into BUG... > > Uh, does any distro really do that?
Apparently, so I was told by Greg a year ago or so when wanting to add WARN_ON(). The advisory is to us pr_warn_once() instead. I rememebr it was a debian based distro.
-- Thanks,
David / dhildenb
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