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[213.175.37.12]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37cbc2a8c2csm858559f8f.20.2024.09.24.00.52.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Sep 2024 00:52:43 -0700 (PDT) Message-ID: Date: Tue, 24 Sep 2024 09:52:42 +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: [PATCH] mm: Make SPLIT_PTE_PTLOCKS depend on the existence of NR_CPUS To: Geert Uytterhoeven , Guenter Roeck Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Masahiro Yamada , linux-kbuild References: <20240923142533.1197982-1-linux@roeck-us.net> <4c2cdf84-9794-4722-8417-cf924f890797@roeck-us.net> <203f0d01-d25e-4436-b769-b89edb1b57d9@roeck-us.net> Content-Language: en-US From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 24.09.24 09:45, Geert Uytterhoeven wrote: > Hi Günter, > > CC kbuild > > I have two comments... > > On Tue, Sep 24, 2024 at 1:52 AM Guenter Roeck wrote: >> On 9/23/24 15:08, Guenter Roeck wrote: >>> On 9/23/24 08:23, David Hildenbrand wrote: >>>> On 23.09.24 16:25, Guenter Roeck wrote: >>>>> SPLIT_PTE_PTLOCKS already depends on "NR_CPUS >= 4", but that evaluates >>>>> to true if there is no NR_CPUS configuration option (such as for m68k). >>>>> This results in CONFIG_SPLIT_PTE_PTLOCKS=y for mac_defconfig. >>>>> This in turn causes the m68k "q800" machine to crash in qemu. > > Should this be fixed in Kconfig (too)? > >>>> Oh, that's why my compile tests still worked ... I even removed the additional NR_CPUS check, assuming it's not required ... >>>> >>>> Thanks for debugging and fixing! >>>> >>>> Acked-by: David Hildenbrand >>>> >>> >>> Apparently it wasn't that simple :-(. 0-day reports a build failure >>> with s390 builds. >>> >>> arch/s390/mm/gmap.c:357:16: error: implicit declaration of function 'pmd_pgtable_page'. >>> >>> Turns out that >>> depends on NR_CPUS && NR_CPUS >= 4 >>> >>> doesn't work and disables SPLIT_PTE_PTLOCKS even if NR_CPUS _is_ defined. >>> I have no idea how to declare the dependency correctly. >>> Sorry, I did not expect that. >> >> The only solution I found was to define NR_CPUS for m68k. That seems to be >> the only architecture not defining it, so hopefully that is an acceptable >> solution. I'll send v2 of the patch shortly. > > My first thought was to agree, as m68k is indeed the only architecture > that does not define NR_CPUS. Upon closer look, most architectures > have NR_CPUS depend on SMP, hence I assume the issue could happen for > those too (although I didn't manage to create such a config on anything I recall that I played the same thing, convincing me that having no CONFIG_NR_CPUS on !SMP would actually do the right thing. Apparently it doesn't for m68k at least. > but m68k)? So the simple solution would be to add a dependency on > SMP to SPLIT_PTE_PTLOCKS. That will probably work for now. CONFIG_NR_CPUS should be cleaned up at some point to sort out the FIXME I commented in v2. Having kconfig set CONFIG_NR_CPUS=1 without SMP would be easiest, but it's probably not that easy. > > BTW, the list of excluded architectures looks fragile to me: > > config SPLIT_PTE_PTLOCKS > def_bool y > depends on MMU > depends on NR_CPUS >= 4 > depends on !ARM || CPU_CACHE_VIPT > depends on !PARISC || PA20 > depends on !SPARC32 > > If this can't be handled in a generic way, perhaps this should be > changed from opt-out to opt-in (i.e. select gate symbol in arch-specific > Kconfig)? Yes, as stated in my commit: More cleanups would be reasonable (like the arch-specific "depends on" for CONFIG_SPLIT_PTE_PTLOCKS), but we'll leave that for another day. -- Cheers, David / dhildenb