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[2003:d8:2f17:9c00:d650:ab5f:74c2:2175]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45df17d9774sm23146765e9.9.2025.09.09.23.45.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Sep 2025 23:45:44 -0700 (PDT) Message-ID: Date: Wed, 10 Sep 2025 08:45:43 +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/hugetlb: fix copy_hugetlb_page_range() to use ->pt_share_count To: Jane Chu , harry.yoo@oracle.com, osalvador@suse.de, liushixin2@huawei.com, muchun.song@linux.dev, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250909184357.569259-1-jane.chu@oracle.com> 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: <20250909184357.569259-1-jane.chu@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 09.09.25 20:43, Jane Chu wrote: > commit 59d9094df3d79 introduced ->pt_share_count dedicated to > hugetlb PMD share count tracking, but omitted fixing > copy_hugetlb_page_range(), leaving the function relying on > page_count() for tracking that no longer works. > > When lazy page table copy for hugetlb is disabled (commit bcd51a3c679d), > fork()'ing with hugetlb PMD sharing quickly lockup - > > [ 239.446559] watchdog: BUG: soft lockup - CPU#75 stuck for 27s! > [ 239.446611] RIP: 0010:native_queued_spin_lock_slowpath+0x7e/0x2e0 > [ 239.446631] Call Trace: > [ 239.446633] > [ 239.446636] _raw_spin_lock+0x3f/0x60 > [ 239.446639] copy_hugetlb_page_range+0x258/0xb50 > [ 239.446645] copy_page_range+0x22b/0x2c0 > [ 239.446651] dup_mmap+0x3e2/0x770 > [ 239.446654] dup_mm.constprop.0+0x5e/0x230 > [ 239.446657] copy_process+0xd17/0x1760 > [ 239.446660] kernel_clone+0xc0/0x3e0 > [ 239.446661] __do_sys_clone+0x65/0xa0 > [ 239.446664] do_syscall_64+0x82/0x930 > [ 239.446668] ? count_memcg_events+0xd2/0x190 > [ 239.446671] ? syscall_trace_enter+0x14e/0x1f0 > [ 239.446676] ? syscall_exit_work+0x118/0x150 > [ 239.446677] ? arch_exit_to_user_mode_prepare.constprop.0+0x9/0xb0 > [ 239.446681] ? clear_bhb_loop+0x30/0x80 > [ 239.446684] ? clear_bhb_loop+0x30/0x80 > [ 239.446686] entry_SYSCALL_64_after_hwframe+0x76/0x7e > > There are two options to resolve the potential latent issue: > 1. remove the PMD sharing awareness from copy_hugetlb_page_range(), > 2. fix it. > This patch opts for the second option. > > Fixes: 59d9094df3d79 ("mm: hugetlb: independent PMD page table shared > count") > > Signed-off-by: Jane Chu > --- > mm/hugetlb.c | 13 ++++--------- > 1 file changed, 4 insertions(+), 9 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 753f99b4c718..8ca5b4f7805f 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5594,18 +5594,13 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, > break; > } > > - /* > - * If the pagetables are shared don't copy or take references. > - * > - * dst_pte == src_pte is the common case of src/dest sharing. > - * However, src could have 'unshared' and dst shares with > - * another vma. So page_count of ptep page is checked instead > - * to reliably determine whether pte is shared. > - */ > - if (page_count(virt_to_page(dst_pte)) > 1) { > +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING > + /* If the pagetables are shared don't copy or take references. */ Why remove so much of the original comment? > + if (ptdesc_pmd_pts_count(virt_to_ptdesc(dst_pte)) > 0) { > addr |= last_addr_mask; > continue; > } LGTM, thanks! -- Cheers David / dhildenb