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[2003:d8:2f25:700:d846:15f3:6ca0:8029]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3d1007c0dc8sm40030772f8f.53.2025.09.08.05.53.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 Sep 2025 05:53:03 -0700 (PDT) Message-ID: <7ee0b58a-8fe4-46fe-bfef-f04f900f3040@redhat.com> Date: Mon, 8 Sep 2025 14:53:00 +0200 Precedence: bulk X-Mailing-List: linux-mips@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 19/37] mm/gup: remove record_subpages() To: Lorenzo Stoakes Cc: John Hubbard , linux-kernel@vger.kernel.org, Alexander Potapenko , Andrew Morton , Brendan Jackman , Christoph Lameter , Dennis Zhou , Dmitry Vyukov , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, iommu@lists.linux.dev, io-uring@vger.kernel.org, Jason Gunthorpe , Jens Axboe , Johannes Weiner , kasan-dev@googlegroups.com, kvm@vger.kernel.org, "Liam R. Howlett" , Linus Torvalds , linux-arm-kernel@axis.com, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-ide@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, Marco Elver , Marek Szyprowski , Michal Hocko , Mike Rapoport , Muchun Song , netdev@vger.kernel.org, Oscar Salvador , Peter Xu , Robin Murphy , Suren Baghdasaryan , Tejun Heo , virtualization@lists.linux.dev, Vlastimil Babka , wireguard@lists.zx2c4.com, x86@kernel.org, Zi Yan References: <20250901150359.867252-1-david@redhat.com> <20250901150359.867252-20-david@redhat.com> <016307ba-427d-4646-8e4d-1ffefd2c1968@nvidia.com> <85e760cf-b994-40db-8d13-221feee55c60@redhat.com> <727cabec-5ee8-4793-926b-8d78febcd623@lucifer.local> From: David Hildenbrand Content-Language: en-US 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <727cabec-5ee8-4793-926b-8d78febcd623@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 08.09.25 14:25, Lorenzo Stoakes wrote: > On Sat, Sep 06, 2025 at 08:56:48AM +0200, David Hildenbrand wrote: >> On 06.09.25 03:05, John Hubbard wrote: >>> >>> Probably a similar sentiment as Lorenzo here...the above diffs make the code >>> *worse* to read. In fact, I recall adding record_subpages() here long ago, >>> specifically to help clarify what was going on. >> >> Well, there is a lot I dislike about record_subpages() to go back there. >> Starting with "as Willy keeps explaining, the concept of subpages do >> not exist and ending with "why do we fill out the array even on failure". > > Yes > >> >> :) >> >>> >>> Now it's been returned to it's original, cryptic form. >>> >> >> The code in the caller was so uncryptic that both me and Lorenzo missed >> that magical addition. :P > > :'( > >> >>> Just my take on it, for whatever that's worth. :) >> >> As always, appreciated. >> >> I could of course keep the simple loop in some "record_folio_pages" >> function and clean up what I dislike about record_subpages(). >> >> But I much rather want the call chain to be cleaned up instead, if possible. >> >> >> Roughly, what I am thinking (limiting it to pte+pmd case) about is the following: > > I cannot get the below to apply even with the original patch here applied + fix. > > It looks like (in mm-new :) commit e73f43a66d5f ("mm/gup: remove dead pgmap > refcounting code") by Alastair has conflicted here, but even then I can't make > it apply, with/without your fix...! To be clear: it was never intended to be applied, because it wouldn't even compile in the current form. It was based on this nth_page submission + fix. [...] >> } >> static int gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, > > OK I guess you intentionally left the rest as a TODO :) > > So I'll wait for you to post it before reviewing in-depth. > > This generally LGTM as an approach, getting rid of *nr is important that's > really horrible. Yes. Expect a cleanup in that direction soonish (again, either from me or someone else I poke) > >> -- >> 2.50.1 >> >> >> >> Oh, I might even have found a bug moving away from that questionable >> "ret==1 means success" handling in gup_fast_pte_range()? Will >> have to double-check, but likely the following is the right thing to do. >> >> >> >> From 8f48b25ef93e7ef98611fd58ec89384ad5171782 Mon Sep 17 00:00:00 2001 >> From: David Hildenbrand >> Date: Sat, 6 Sep 2025 08:46:45 +0200 >> Subject: [PATCH] mm/gup: fix handling of errors from >> arch_make_folio_accessible() in follow_page_pte() >> >> In case we call arch_make_folio_accessible() and it fails, we would >> incorrectly return a value that is "!= 0" to the caller, indicating that >> we pinned all requested pages and that the caller can keep going. >> >> follow_page_pte() is not supposed to return error values, but instead >> 0 on failure and 1 on success. >> >> That is of course wrong, because the caller will just keep going pinning >> more pages. If we happen to pin a page afterwards, we're in trouble, >> because we essentially skipped some pages. >> >> Fixes: f28d43636d6f ("mm/gup/writeback: add callbacks for inaccessible pages") >> Signed-off-by: David Hildenbrand >> --- >> mm/gup.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/mm/gup.c b/mm/gup.c >> index 22420f2069ee1..cff226ec0ee7d 100644 >> --- a/mm/gup.c >> +++ b/mm/gup.c >> @@ -2908,8 +2908,7 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr, >> * details. >> */ >> if (flags & FOLL_PIN) { >> - ret = arch_make_folio_accessible(folio); >> - if (ret) { >> + if (arch_make_folio_accessible(folio)) { > > Oh Lord above. Lol. Yikes. > > Yeah I think your fix is valid... I sent it out earlier today. Fortunately that function shouldn't usually really fail IIUC. -- Cheers David / dhildenb