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[2003:d8:2f27:6d00:7b96:afc9:83d0:5bd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-462c17c9347sm10474045e9.0.2025.09.17.08.44.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Sep 2025 08:44:32 -0700 (PDT) Message-ID: Date: Wed, 17 Sep 2025 17:44:31 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC][PATCH v3 09/16] genirq/irqdesc: Have nr_irqs as non-static To: Eugen Hristev , Thomas Gleixner , linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, andersson@kernel.org, pmladek@suse.com, rdunlap@infradead.org, corbet@lwn.net, mhocko@suse.com Cc: tudor.ambarus@linaro.org, mukesh.ojha@oss.qualcomm.com, linux-arm-kernel@lists.infradead.org, linux-hardening@vger.kernel.org, jonechou@google.com, rostedt@goodmis.org, linux-doc@vger.kernel.org, devicetree@vger.kernel.org References: <20250912150855.2901211-1-eugen.hristev@linaro.org> <20250912150855.2901211-10-eugen.hristev@linaro.org> <87cy7q9k8y.ffs@tglx> <87a52u9jyl.ffs@tglx> <8df2cf28-c15e-4692-a127-6a5c966a965e@linaro.org> <2bd45749-e483-45ea-9c55-74c5ba15b012@redhat.com> <87v7lh891c.ffs@tglx> <95ff36c2-284a-46ba-984b-a3286402ebf8@redhat.com> <24d6a51d-f5f8-44d7-94cb-58b71ebf473a@linaro.org> <7f4aa4c6-7b77-422b-9f7a-d01530c54bff@redhat.com> <10540b3e-09ca-403d-bc20-b9412a7fe28a@linaro.org> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.09.25 17:32, Eugen Hristev wrote: > > > On 9/17/25 18:18, David Hildenbrand wrote: >> On 17.09.25 17:02, Eugen Hristev wrote: >>> >>> >>> On 9/17/25 17:46, David Hildenbrand wrote: >>>> On 17.09.25 16:10, Thomas Gleixner wrote: >>>>> On Wed, Sep 17 2025 at 09:16, David Hildenbrand wrote: >>>>>> On 17.09.25 07:43, Eugen Hristev wrote: >>>>>>> On 9/17/25 00:16, Thomas Gleixner wrote: >>>>>>>> I pointed you to a solution for that and just because David does not >>>>>>>> like it means that it's acceptable to fiddle in subsystems and expose >>>>>>>> their carefully localized variables. >>>>>> >>>>>> It would have been great if we could have had that discussion in the >>>>>> previous thread. >>>>> >>>>> Sorry. I was busy with other stuff and did not pay attention to that >>>>> discussion. >>>> >>>> I understand, I'm busy with too much stuff such that sometimes it might >>>> be good to interrupt me earlier: "David, nooo, you're all wrong" >>>> >>>>> >>>>>> Some other subsystem wants to have access to this information. I agree >>>>>> that exposing these variables as r/w globally is not ideal. >>>>> >>>>> It's a nono in this case. We had bugs (long ago) where people fiddled >>>>> with this stuff (I assume accidentally for my mental sanity sake) and >>>>> caused really nasty to debug issues. C is a horrible language to >>>>> encapsulate stuff properly as we all know. >>>> >>>> Yeah, there is this ACCESS_PRIVATE stuff but it only works with structs >>>> and relies on sparse IIRC. >>>> >>>>> >>>>>> I raised the alternative of exposing areas or other information through >>>>>> simple helper functions that kmemdump can just use to compose whatever >>>>>> it needs to compose. >>>>>> >>>>>> Do we really need that .section thingy? >>>>> >>>>> The section thing is simple and straight forward as it just puts the >>>>> annotated stuff into the section along with size and id and I definitely >>>>> find that more palatable, than sprinkling random functions all over the >>>>> place to register stuff. >>>>> >>>>> Sure, you can achieve the same thing with an accessor function. In case >>>>> of nr_irqs there is already one: irq_get_nr_irqs(), but for places which >>>> >>>> Right, the challenge really is that we want the memory range covered by >>>> that address, otherwise it would be easy. >>>> >>>>> do not expose the information already for real functional reasons adding >>>>> such helpers just for this coredump muck is really worse than having a >>>>> clearly descriptive and obvious annotation which results in the section >>>>> build. >>>> >>>> Yeah, I'm mostly unhappy about the "#include " stuff. >>>> >>>> Guess it would all feel less "kmemdump" specific if we would just have a >>>> generic way to tag/describe certain physical memory areas and kmemdump >>>> would simply make use of that. >>> >>> The idea was to make "kmemdump" exactly this generic way to tag/describe >>> the memory. >> >> That's probably where I got lost, after reading the cover letter >> assuming that this is primarily to program kmemdump backends, which I >> understood to just special hw/firmware areas, whereby kinfo acts as a >> filter. > > If there is a mechanism to tag all this memory, or regions, into a > specific section, what we would do with it next ? > It would have a purpose to be parsed and reused by different drivers, > that would be able to actually use it. > So there has a to be some kind of middleman, that holds onto this list > of regions, manages it (unique id, add/remove), and allows certain > drivers to use it. Right, just someone that maintains the list and possibly allows traversing the list and possibly getting notifications on add/remove. > Now it would be interesting to have different kind of drivers connect to > it (or backends how I called them). > One of these programs an internal table for the firmware to use. > Another , writes information into a dedicated reserved-memory for the > bootloader to use on the next soft reboot (memory preserved). > I called this middleman kmemdump. But it can be named differently, and > it can reside in different places in the kernel. > But what I would like to avoid is to just tag all this memory and have > any kind of driver connect to the table. That works, but it's quite > loose on having control over the table. E.g. no kmemdump, tag all the > memory to sections, and have specific drivers (that would reside where?) > walk it. Yeah, you want just some simple "registry" with traversal+notification. > >> >>> If we would call it differently , simply dump , would it be better ? >>> e.g. include linux/dump.h >>> and then DUMP(var, size) ? >>> >>> could we call it maybe MARK ? or TAG ? >>> TAG_MEM(area, size) Just because I thought about it again, "named memory" could be an alternative to "tagged memory". -- Cheers David / dhildenb