On 5/16/22 1:07 PM, Thorsten Leemhuis wrote: > > > On 16.05.22 20:39, Jens Axboe wrote: >> On 5/16/22 12:34 PM, Thorsten Leemhuis wrote: >>> On 16.05.22 20:22, Jens Axboe wrote: >>>> On 5/16/22 12:17 PM, Thorsten Leemhuis wrote: >>>>>>> Pavel, I had actually just started a draft email with the same theory >>>>>>> (although you stated it much more clearly than I could have). I'm >>>>>>> working on debugging the LXC side, but I'm pretty sure the issue is >>>>>>> due to LXC using blocking reads and getting stuck exactly as you >>>>>>> describe. If I can confirm this, I'll go ahead and mark this >>>>>>> regression as invalid and file an issue with LXC. Thanks for your help >>>>>>> and patience. >>>>>> >>>>>> Yes, it does appear that was the problem. The attach POC patch against >>>>>> LXC fixes the hang. The kernel is working as intended. >>>>>> >>>>>> #regzbot invalid: userspace programming error >>>>> >>>>> Hmmm, not sure if I like this. So yes, this might be a bug in LXC, but >>>>> afaics it's a bug that was exposed by kernel change in 5.17 (correct me >>>>> if I'm wrong!). The problem thus still qualifies as a kernel regression >>>>> that normally needs to be fixed, as can be seen my some of the quotes >>>>> from Linus in this file: >>>>> https://www.kernel.org/doc/html/latest/process/handling-regressions.html >>>> >>>> Sorry, but that's really BS in this particularly case. This could always >>>> have triggered, it's the way multishot works. Will we count eg timing >>>> changes as potential regressions, because an application relied on >>>> something there? That does not make it ABI. >>>> >>>> In general I agree with Linus on this, a change in behavior breaking >>>> something should be investigated and figured out (and reverted, if need >>>> be). This is not that. >>> >>> Sorry, I have to deal with various subsystems and a lot of regressions >>> reports. I can't know the details of each of issue and there are >>> developers around that are not that familiar with all the practical >>> implications of the "no regressions". That's why I was just trying to >>> ensure that this is something safe to ignore. If you say it is, than I'm >>> totally happy and now rest my case. :-D >> >> It's just a slippery slope that quickly leads to the fact that _any_ >> kernel change is a potential regressions, > > I know, don't worry, that's why I'm trying to be careful. But I also had > cases already where someone (even a proper subsystem maintainer) said > "this is not a regression, it's a userspace bug" and it clearly was a > kernel regression (and Linus wasn't happy when he found out). That why I I get where you're coming from, and that is indeed what most maintainers would say :-) -- Jens Axboe
