From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: dovetail: add prctl() call form References: <5283f8ff-33bf-910d-25b5-044ea6a963ae@siemens.com> <87a6iepm0x.fsf@xenomai.org> <871r3ppq5w.fsf@xenomai.org> <87k0hhdwkn.fsf@xenomai.org> <5fae03f0-0129-05b6-fcce-0be07707a501@siemens.com> <875yt0ct4b.fsf@xenomai.org> <345ce43f-ce6f-703f-89b2-b82b3fa5b4c6@siemens.com> <87y25wbcu2.fsf@xenomai.org> <4a41295f-63f0-c6e7-5769-8c19b2235051@siemens.com> <87h7ckb6tk.fsf@xenomai.org> From: Jan Kiszka Message-ID: <8f7c1316-0565-3e74-3c78-dac9ef5b328c@siemens.com> Date: Wed, 10 Nov 2021 13:16:03 +0100 MIME-Version: 1.0 In-Reply-To: <87h7ckb6tk.fsf@xenomai.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Philippe Gerum Cc: Xenomai On 10.11.21 12:14, Philippe Gerum wrote: > > Jan Kiszka writes: > >> On 10.11.21 09:58, Philippe Gerum wrote: >>> >>> Jan Kiszka writes: >>> >>>> On 10.11.21 08:38, Philippe Gerum wrote: >>>>> >>>>> Jan Kiszka writes: >>>>> >>>>>> On 09.11.21 14:35, Philippe Gerum wrote: >>>>>>> >>>>>>> Jan Kiszka writes: >>>>>>> >>>>>>>> On 09.11.21 11:23, Philippe Gerum wrote: >>>>>>>>> >>>>>>>>> Jan Kiszka writes: >>>>>>>>> >>>>>>>>>> On 08.11.21 18:57, Philippe Gerum wrote: >>>>>>>>>>> >>>>>>>>>>> Jan Kiszka writes: >>>>>>>>>>> >>>>>>>>>>>> Hi Philippe, >>>>>>>>>>>> >>>>>>>>>>>> this dovetail commit makes the pipeline go red, crashing the kernels >>>>>>>>>>>> (e.g. [1][2]). I hope this is something we can quickly fix in dovetail, >>>>>>>>>>>> maybe via a config option? >>>>>>>>>>>> >>>>>>>>>>>> Jan >>>>>>>>>>>> >>>>>>>>>>>> [1] https://source.denx.de/Xenomai/xenomai-images/-/jobs/348118#L966 >>>>>>>>>>>> [2] https://source.denx.de/Xenomai/xenomai-images/-/jobs/348121#L1429 >>>>>>>>>>> >>>>>>>>>>> Cobalt needs some update to cope with this now. I'll send a fix either >>>>>>>>>>> way (dovetail or xenomai) tomorrow morning. >>>>>>>>>> >>>>>>>>>> This should be fixed in dovetail - API breakage. We can update Xenomai >>>>>>>>>> later, along with enabling this feature again. >>>>>>>>>> >>>>>>>>> >>>>>>>>> We now have a change in the Dovetail tree which handles the fact that >>>>>>>>> some Dovetail-based core might lag behind a bit API-wise regarding the >>>>>>>>> new prctl-based call form. Since this simplifies the handling for any >>>>>>>>> companion core in that particular case, this seems legitimate to add >>>>>>>>> it. Tested on kvm-x86, -aarch64, and i.MX6-sabre with both Cobalt and >>>>>>>>> EVL cores. Both test suites run properly, so far so good. >>>>>>>> >>>>>>>> I'm not against this change, but activating it is no Xenomai 3.2 >>>>>>>> material as it will break the ABI. >>>>>>> >>>>>>> No, the ABI has never been affected by this series, the old call form >>>>>>> Cobalt uses is still supported, the new prctl() call form is a mere >>>>>>> addition, not a replacement. The problem did only affect the kernel >>>>>>> interface between the pipeline core and Cobalt, which is strictly a >>>>>>> kernel API issue, not revealed by my tests mainly with Xenomai4/EVL >>>>>>> unfortunately. >>>>>> >>>>>> The whole purpose of having this addition is using it. And that does >>>>>> make a lot of sense, as you described. So the plan is to activate AND >>>>>> use this feature in Xenomai 3.3 - with the aforementioned impact on the ABI. >>>>>> >>>>>> Xenomai 3.2 will continue to use the old syscall range extension scheme, >>>>>> thus as no need and no desire to enable reporting of prctl calls to the >>>>>> core. Therefore, Dovetail should continue to refrain from doing that for >>>>>> Xenomai 3.2. The easiest way to achieve that is making the extension >>>>>> build-time configurable. Other cores can then still enable it for their >>>>>> *use*, and the fresh Xenomai 3.2 release will not break over the next >>>>>> dovetail patch revision (which is urgently needed do to the apic-ack fix). >>>>>> >>>>>> Makes sense? >>>>>> >>>>> >>>>> It falls short of solving the real problem. >>>> >>>> Nor does your approach. If it were consequently ignoring stable >>>> interfaces - there is no need for it in your in-tree model -, it would >>>> have simply dropped the old syscall interface. Instead, it only provided >>>> a half-stable solution for its users. >>>> >>> >>> It looks ok so far on this end, thanks for caring anyway. >>> >>>>> >>>>>> I really like to avoid avoid diverging developments again, but stability >>>>>> trumps features and would enforce this if we cannot find a better solution. >>>>>> >>>>> >>>>> I agree, the best way is to decouple the code bases at this point, so >>>>> that all development efforts can progress at their own pace, according >>>>> to their own agenda and schedule, which are not compatible. Opening a >>>>> new tree for maintaining a Xenomai3-specific pipeline will: >>>>> >>>>> - make things clearer to Xenomai3 users, providing them an unambiguous >>>>> source for getting Dovetail support that works for it. >>>>> >>>>> - give you full control over this Dovetail tree, what goes there from >>>>> the upstream code and what does not, when it does if it does. >>>>> >>>>> - keep all options open for the Dovetail upstream development. The >>>>> whole point of starting Dovetail was to be able to evolve the dual >>>>> kernel integration technique based on the evolving implementation of >>>>> the mainline kernel, instead of being stuck for ages with legacy >>>>> kernel interfaces. Kernel API changes are part of this process. >>>>> >>>>> We can cross-pollinate the trees, until Xenomai3 rebases on the next >>>>> linux SLTS release which Dovetail upstream would support, and so on. >>>>> >>>> >>>> As I said, this is very unfortunate, and I hope you will reconsider your >>>> decisions. >>>> >>> >>> I don't think this is a bad thing. This clarifies the intent, making >>> things easier in the long run. >>> >>>> Meanwhile, I will stop 5.10.y-dovetail and instead start >>>> linux-dovetail-stable.git with related branches. CI will be migrated as >>>> well, stopping coverage of linux-dovetail head. >>> >>> Please call it linux-xenomai3-dovetail or anything you see fit except >>> linux-dovetail-stable. Stability has a different meaning, and this name >>> should be reserved for an upstream Dovetail tree. TIA, >>> >> >> The result will not be Xenomai 3 specific. It will just use stable APIs >> as additional requirement, perform the merge-based development process >> for stable branches and provide regular CI-qualified releases again. >> Just like under I-pipe. >> > > Just find another name than linux-dovetail-stable, the rest is fine. > dovetail-standlone created - but disabled again for now. https://source.denx.de/Xenomai/linux-dovetail/-/commit/8e3e74e0ce26c0ed146a65525c2c45465717ac58 widely mitigates the issue for 3.2. You can still trigger the BUG via invalid prctl calls, but that can be ignored and will be resolved in 3.2.1. Thanks, Jan -- Siemens AG, T RDA IOT Corporate Competence Center Embedded Linux