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b=fZLLXGgImx9TODyKrsAZATl2CLQRWhm4jFBxozmhe8EFqK/rDLFcc+rfSfHj2MD0M BWsDFoWK4TOmELcImdTcActnUZM4VT6UAFN76l76QFNpncSYha9PTldrxQw2YjAc75 BHhY4gvN+krCpXwJoKxVeuZZodZo9sMBImDdGrnUHfbjuYFR8lPLilAAVACr9Var21 UdOU7fIU4Zahk1J2RXAPRtprWmx4mDgbxZHF124azE39oJaPo9AbYIg9kn7stS2Od6 Hmk2agEza9eZuqnHN9zDYWQU3WQYlvywYC4rJjPux76oOjW3m+lDXAfhGLGB0pkpxJ f4zwPl4C2b2Yg== Message-ID: <4aad3847-4240-40aa-af24-df34da4d68ad@kernel.org> Date: Thu, 1 Oct 2026 09:00:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/memory_hotplug: fix missing rollback in __add_pages() To: Muchun Song Cc: Lance Yang , osalvador@suse.de, akpm@linux-foundation.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260930160432.5564-1-lance.yang@linux.dev> <203892F4-B04A-4F69-A1B3-DC1619176C67@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <203892F4-B04A-4F69-A1B3-DC1619176C67@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: rfcnwuasf53j7dgferfxtjhmnshzhwip X-Rspamd-Queue-Id: 6B7C180010 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1790838061-86074 X-HE-Meta: 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 OjZnjGIH DHrrxC/VwIFAeUgNBvz7Rxn/uorGcOMMYf7Wdpe9xLRMpAVZ/19fcq6zL1icqaqae/i0UMw5JxBeelZtQ32vKd6+joeQJjCq7WBPR+jAOtK8xza3zVuZ0EQEa/LWWwXIa6UuQt31MOtMXCP4hM70RS2eU1gOBcI1JZxyIdMoKX21NS+xhATFPSVfRzNtpSNjj3Zx7QtdQVXuCNjlGHh+YMBKV7OmrwyuID1aT2XdiShEtNfmSTSXwiQTG/P+wZKVzZW8r5vgt2DjGj4sT2zrzwMR9tNFU1xtrRLUlZSNOVH+wwBau7Y6lJBF6jD2VQ3Crky3I8gGblqhh/iCT2tIrQwwo3k08f6w/7eGtr1E4bplUhjw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/1/26 04:33, Muchun Song wrote: > > >> On Oct 1, 2026, at 00:46, David Hildenbrand (Arm) wrote: >> >> On 9/30/26 18:04, Lance Yang wrote: >>> __add_pages() returns on a sparse_add_section() failure without removing >>> the sections already added in the same request. >>> >>> For memremap_pages(), the failed range is not counted in pgmap->nr_range, >>> so memunmap_pages() skips it. The sections already added in that range >>> retain their vmemmap mappings and subsection bits. Retrying a >>> section-aligned range can then fail with -EEXIST. >>> >>> Save the initial PFN and remove [start_pfn, pfn) on failure. For a vmemmap >>> population failure, section_activate() already cleans up the current >>> section, so the rollback excludes it. If the first section fails, >>> __remove_pages() receives an empty range and does nothing. >>> >>> Link: https://lore.kernel.org/all/BAD58999-1EDD-4A37-ABA0-DB1BD8AB3453@linux.dev/ >>> Suggested-by: Muchun Song >>> Signed-off-by: Lance Yang >>> --- >>> No Fixes tag, as I couldn't identify the commit that introduced this issue. >>> >>> mm/memory_hotplug.c | 6 +++++- >>> 1 file changed, 5 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index 796af1028ee2..ca4656698148 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -380,6 +380,7 @@ EXPORT_SYMBOL_GPL(pfn_to_online_page); >>> int __add_pages(int nid, unsigned long pfn, unsigned long nr_pages, >>> struct mhp_params *params) >>> { >>> + const unsigned long start_pfn = pfn; >>> const unsigned long end_pfn = pfn + nr_pages; >>> unsigned long cur_nr_pages; >>> int err; >>> @@ -413,8 +414,11 @@ int __add_pages(int nid, unsigned long pfn, unsigned long nr_pages, >>> SECTION_ALIGN_UP(pfn + 1) - pfn); >>> err = sparse_add_section(nid, pfn, cur_nr_pages, altmap, >>> params->pgmap); >>> - if (err) >>> + if (err) { >>> + __remove_pages(start_pfn, pfn - start_pfn, altmap, >>> + params->pgmap); >>> break; >>> + } >>> cond_resched(); >>> } >>> vmemmap_populate_print_last(); >> >> Makes sense and LGTM. >> >> Do we have a Fixes: tag? It probably dates back quite a while ... not sure about >> stable, we never saw this in practice. But if it's easy, we should just do it? >> (not sure if we ever had __remove_pages be limited to hotunplug support) >> >> I'm planning on picking this up and sending it for the next merge window (so not >> as a hotfix). >> >> Looking at this ... >> >> x86 does not really expect add_pages to fail: >> >> ret = __add_pages(nid, start_pfn, nr_pages, params); >> WARN_ON_ONCE(ret); >> >> That's probably something to clean up as well? > > The warning is a historical leftover. The original code > printed an error when __add_pages() failed. Commit > 10f22dde556d accidentally turned that conditional printk > into an unconditional WARN_ON(1), and commit fe8b868eccb9 > subsequently changed it to WARN_ON_ONCE(ret) to avoid > warning on successful memory hot-add. > > There is no no-failure contract here: __add_pages() can > legitimately return errors such as -ENOMEM, and those > errors are already propagated to the caller. Since > WARN_ON_ONCE(ret) has no effect on control flow or error > handling, it can be safely removed without changing the > failure semantics. We do not want to WARN_ON in any situation that can legitimately happen. So this should be sorted out (and Lance is on it IIUC :) ) > > This also reveals a potential bug introduced by commit > ea0854170c952: when update_end_of_memory_vars() was > added, it was called without checking that ret == 0, so the > end-of-memory variables may be updated even when > __add_pages() fails. Returning immediately on error fixes > that as well. I'd assume the end-of-memory variables are not a problem, as we usually do not adjust them during memory unplug either. But yeah, ideally we wouldn't update them (like other architectures do IIRC). -- Cheers, David