Messages in this thread | | | Date | Tue, 16 Nov 2021 11:34:17 +0300 | Subject | Re: [PATCH v2 0/2] Introduce the pkill_on_warn parameter | From | Alexander Popov <> |
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On 16.11.2021 09:37, Christophe Leroy wrote: > Le 15/11/2021 à 17:06, Steven Rostedt a écrit : >> On Mon, 15 Nov 2021 14:59:57 +0100 >> Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote: >> >>> 1. Allow a reasonably configured kernel to boot and run with >>> panic_on_warn set. Warnings should only be raised when something is >>> not configured as the developers expect it or the kernel is put into a >>> state that generally is _unexpected_ and has been exposed little to >>> the critical thought of the developer, to testing efforts and use in >>> other systems in the wild. Warnings should not be used for something >>> informative, which still allows the kernel to continue running in a >>> proper way in a generally expected environment. Up to my knowledge, >>> there are some kernels in production that run with panic_on_warn; so, >>> IMHO, this requirement is generally accepted (we might of course >> >> To me, WARN*() is the same as BUG*(). If it gets hit, it's a bug in the >> kernel and needs to be fixed. I have several WARN*() calls in my code, and >> it's all because the algorithms used is expected to prevent the condition >> in the warning from happening. If the warning triggers, it means either that >> the algorithm is wrong or my assumption about the algorithm is wrong. In >> either case, the kernel needs to be updated. All my tests fail if a WARN*() >> gets hit (anywhere in the kernel, not just my own). >> >> After reading all the replies and thinking about this more, I find the >> pkill_on_warning actually worse than not doing anything. If you are >> concerned about exploits from warnings, the only real solution is a >> panic_on_warning. Yes, it brings down the system, but really, it has to be >> brought down anyway, because it is in need of a kernel update. >> > > We also have LIVEPATCH to avoid bringing down the system for a kernel > update, don't we ? So I wouldn't expect bringing down a vital system > just for a WARN.
Hello Christophe,
I would say that different systems have different requirements. Not every Linux-based system needs live patching (it also has own limitations).
That's why I proposed a sysctl and didn't change the default kernel behavior.
> As far as I understand from > https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on, > WARN() and WARN_ON() are meant to deal with those situations as > gracefull as possible, allowing the system to continue running the best > it can until a human controled action is taken.
I can't agree here. There is a very strong push against adding BUG*() to the kernel source code. So there are a lot of cases when WARN*() is used for severe problems because kernel developers just don't have other options.
Currently, it looks like there is no consistent error handling policy in the kernel.
> So I'd expect the WARN/WARN_ON to be handled and I agree that that > pkill_on_warning seems dangerous and unrelevant, probably more dangerous > than doing nothing, especially as the WARN may trigger for a reason > which has nothing to do with the running thread.
Sorry, I see a contradiction. If killing a process hitting a kernel warning is "dangerous and unrelevant", why killing a process on a kernel oops is fine? That's strange.
Linus calls that behavior "fairly benign" here: http://lkml.iu.edu/hypermail/linux/kernel/1610.0/01217.html
Best regards, Alexander
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