From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B6C693CB540; Wed, 9 Sep 2026 14:44:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788965075; cv=none; b=a7G0gssj3vyIHBaiemz4UePfAYErWIwepk10R5DST3PFfXxPzXWrZfY8GvYjWAxj1igKpubknkkUir9Jvj/JQ+TxVR8cYmGOdQG+kJLd7YfosXSRpfEH2MaHL7vxnedJc+r5d4hE87XGg+bXWLrXkDatUBpRsvpLJrjhOIWlbfs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788965075; c=relaxed/simple; bh=bcRwefqWL8yLZa9DFjrrXLH3J4fyyyLy/rbqxf2tVWM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=X6GntyzfHy1QXbLRvxmN5szwOsH0Gb5PikYe/7ek1PO7w2bRC8xuEwOXkUEclb7h4i+0yy0ODtPta0NCWOanHQKU5mL/ZFANUg09U7zc/+luQEwPNZwipllUshKTkTHcXzsg6EGlfe3dD3CPdvl+gwEBZqCIixRlYbRZqhe0Gqg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hPtBvy3I; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hPtBvy3I" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9D29C1F00A3A; Wed, 9 Sep 2026 14:44:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788965074; bh=DKryHpZeZQ6KARApTW1tXfW8/qhqsgo+z43g+o2hGEw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=hPtBvy3IN+9aQnyz4FjXUv2U35jR+DaFAk4MR+MsSrqQhLw/B1mnW4ZEPKZrpTdE+ 5Ogl8ftbNdUYWnFiaFYJWzmD8F4P3iY1EPetUNz1Wwal0BHGoCqh2+bUQ7B3jW6Ft+ DBiXy07xw4822CYgZWg666kPfO+OZtSSSXG6+YMavsrtZVwj8xa6MdG2D3k8iN6zH9 zPK16JXMPsihlHKcb+Oe5URKgUnWWRkpWPLTvreGXHRPgldujKKXElm7QEefThm5j5 7Xh6Q+pq+YTVKa1gIiDi7gO3NOt6xZ4daMQ6uJgLDq1fpTeEQVbizUDUbF7xulthht k7g1XmTUjheLQ== Message-ID: <0a7c5147-c193-417d-b1e0-203d9de11247@kernel.org> Date: Wed, 9 Sep 2026 16:44:24 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 08/12] mm/sparse: move __highest_used_section_nr handling To: Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , Brendan Jackman , Johannes Weiner , Zi Yan , Oscar Salvador , Greg Kroah-Hartman , "Rafael J. Wysocki" , Danilo Krummrich , Jan Kiszka , Kieran Bingham Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org, driver-core@lists.linux.dev, linux-fsdevel@vger.kernel.org References: <20260909-b4-sparsemem_cleanups-v1-0-008fc8d579fe@kernel.org> <20260909-b4-sparsemem_cleanups-v1-8-008fc8d579fe@kernel.org> 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: <20260909-b4-sparsemem_cleanups-v1-8-008fc8d579fe@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/9/26 15:33, David Hildenbrand (Arm) wrote: > Let's move it to sparse_init_one_section(). However, to keep early > boot processing working, we also have to initialize it in > sparse_sections_init(). > > Should we use READ_ONCE/WRITE_ONCE with __highest_used_section_nr? > Probably, something for another day. > > Signed-off-by: David Hildenbrand (Arm) > --- > mm/sparse.c | 5 +++-- > mm/sparse.h | 6 +++--- > 2 files changed, 6 insertions(+), 5 deletions(-) > > diff --git a/mm/sparse.c b/mm/sparse.c > index 2b41ae36f20b8..2d0f2db34f4cf 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -177,7 +177,7 @@ static inline unsigned long first_present_section_nr(void) > > void __init sparse_sections_init(void) > { > - unsigned long pfn, start_pfn, end_pfn; > + unsigned long pfn, start_pfn, end_pfn, section_nr; > int i, nid; > > sparse_extreme_init(); > @@ -187,9 +187,9 @@ void __init sparse_sections_init(void) > mminit_validate_memmodel_limits(&start_pfn, &end_pfn); > > for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) { > - unsigned long section_nr = pfn_to_section_nr(pfn); > struct mem_section *ms; > > + section_nr = pfn_to_section_nr(pfn); > sparse_index_init(section_nr, nid); > ms = __nr_to_section(section_nr); > if (ms->section_mem_map) > @@ -201,6 +201,7 @@ void __init sparse_sections_init(void) > __section_mark_present(ms, section_nr); > } > } > + __highest_used_section_nr = section_nr; > } Sashiko says that section_nr could be used uninitialized if the loop body doesn't run. Certainly a very high regression. In a universe where a machine can boot without any memory? "This could occur if mminit_validate_memmodel_limits() clamps start_pfn and end_pfn to the same value, or if for_each_mem_pfn_range() yields no memory ranges." I think this can be ignored. Sashiko also thinks it found a pre-existing issue when updating ms->section_mem_map in sparse_init_one_section() when subsections already exist. That would be the case during ZONE_DEVICE hotplug only. Likely we should skip the sparse_init_one_section() if already initialized. I'll add this to my todo, but it has low priority. -- Cheers, David