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[80.187.83.110]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e723431f5sm156675695e9.2.2025.10.06.06.25.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Oct 2025 06:26:00 -0700 (PDT) Message-ID: <1d5df7c9-8eec-49ad-b4c7-39c70bd172d7@redhat.com> Date: Mon, 6 Oct 2025 15:25:58 +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: [syzbot] [arm?] WARNING in copy_highpage To: Catalin Marinas Cc: syzbot , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, will@kernel.org, Kefeng Wang References: <68dda1ae.a00a0220.102ee.0065.GAE@google.com> <7af02ceb-563a-4bad-84ee-620aaa513bed@redhat.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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 06.10.25 15:17, Catalin Marinas wrote: > On Mon, Oct 06, 2025 at 09:55:27AM +0200, David Hildenbrand wrote: >>>> Modules linked in: >>>> CPU: 1 UID: 0 PID: 25189 Comm: syz.2.7336 Not tainted syzkaller #0 PREEMPT >>>> Hardware name: linux,dummy-virt (DT) >>>> pstate: 00402009 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) >>>> pc : copy_highpage+0x150/0x334 arch/arm64/mm/copypage.c:55 >>>> lr : copy_highpage+0xb4/0x334 arch/arm64/mm/copypage.c:25 >>>> sp : ffff800088053940 >>>> x29: ffff800088053940 x28: ffffc1ffc0acf800 x27: ffff800088053b10 >>>> x26: ffffc1ffc0acf808 x25: ffffc1ffc037b1c0 x24: ffffc1ffc037b1c0 >>>> x23: ffffc1ffc0acf800 x22: ffffc1ffc0acf800 x21: fff000002b3e0000 >>>> x20: fff000000dec7000 x19: ffffc1ffc037b1c0 x18: 0000000000000000 >>>> x17: fff07ffffcffa000 x16: ffff800080008000 x15: 0000000000000001 >>>> x14: 0000000000000000 x13: 0000000000000003 x12: 000000000006d9ad >>>> x11: 0000000000000000 x10: 0000000000000010 x9 : 0000000000000000 >>>> x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000 >>>> x5 : ffff800088053b18 x4 : ffff80008032df94 x3 : 00000000ff000000 >>>> x2 : 01ffc00003000001 x1 : 01ffc00003000001 x0 : 01ffc00003000001 >>>> Call trace: >>>> try_page_mte_tagging arch/arm64/include/asm/mte.h:93 [inline] (P) >>>> copy_highpage+0x150/0x334 arch/arm64/mm/copypage.c:55 (P) >>>> copy_mc_highpage include/linux/highmem.h:383 [inline] >>>> folio_mc_copy+0x44/0x6c mm/util.c:740 >>>> __migrate_folio.constprop.0+0xc4/0x23c mm/migrate.c:851 >>>> migrate_folio+0x1c/0x2c mm/migrate.c:882 >>>> move_to_new_folio+0x58/0x144 mm/migrate.c:1097 >>>> migrate_folio_move mm/migrate.c:1370 [inline] >>>> migrate_folios_move mm/migrate.c:1719 [inline] >>>> migrate_pages_batch+0xaf4/0x1024 mm/migrate.c:1966 >>>> migrate_pages_sync mm/migrate.c:2023 [inline] >>>> migrate_pages+0xb9c/0xcdc mm/migrate.c:2105 >>>> do_mbind+0x20c/0x4a4 mm/mempolicy.c:1539 >>>> kernel_mbind mm/mempolicy.c:1682 [inline] >>>> __do_sys_mbind mm/mempolicy.c:1756 [inline] >>> >>> I don't think we ever stressed MTE with mbind before. I have a suspicion >>> this problem has been around for some time. >>> >>> My reading of do_mbind() is that it ends up allocating pages for >>> migrating into via alloc_migration_target_by_mpol() -> >>> folio_alloc_mpol(). Pages returned should be untagged and uninitialised >>> unless the PG_* flags have not been cleared on a prior free. Or >>> migrate_pages_batch() somehow reuses some pages instead of reallocating. >> >> Staring at __migrate_folio(), I assume we can end up successfully calling >> folio_mc_copy(), but then failing in __folio_migrate_mapping(). >> >> Seems to be as easy as failing the folio_ref_freeze() in >> __folio_migrate_mapping(). >> >> We return -EAGAIN in that case, making the caller retry, stumbling into an >> already-tagged page. (with the same source / destination parameters) IIRC) >> >> So likely this is simply us re-doing the copy after a migration failed after >> the copy. >> >> Could it happen that we are calling it with a different source/destination >> combination the second time? I don't think so, but I am not 100% sure. > > Thanks David. I can now see how it would retry on the same pages without > reallocating. At least we know it's not causing any side-effects, only > messing up the MTE safety warnings. As long as the folio is not getting reused elsewhere, yes. I haven't fully understood yet if there could be cases where we use the folio for another source. But I think it's not trivially possible, because I think we allocate dst folios based on source-folio properties (order, node, zone, etc). > >> The most reliable way would be to un-tag in case folio_mc_copy succeeded but >> __folio_migrate_mapping() failed. > > Clearing an MTE specific flag in the core code doesn't look great. Also > going for some generic mask like PAGE_FLAGS_CHECK_AT_PREP may have > side-effects as we don't know where the page is coming from (we have > those get_new_folio()/put_new_folio() arguments passed on by higher up > callers). As an alternative, I would probably have done something like providing a simple folio_mc_copy_abort(). > > I'm tempted to just drop the warning in the arm64 copy_highpage(), > replace it with a comment about migration retrying on a potentially > tagged page. It will have to override the tags each time (as it > currently does but also warns). Works for me. Maybe we could warn if the tag would change, because I think after we unmapped the folio during migration, the tag can no longer change. -- Cheers David / dhildenb