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b=RxuFM0wY/cj9ZVZuXnbwdE9wkU5NWx4mgNDUShlyhw7Hi88NJ2VqAvCJ35KJ2VZbV 7LRIE1WsFcrJWamJPHk88WOXG4u/v0atDLLKcOiH6RjbuMwBCeZ+Nm5xj5wjJVZ7s6 fwX/ePZnBS1XJdbYm9AVh3Nl4eSGJf4oh/jNlz5DZhf0kD7y9fYTD++Z255qRx91Gh CNTdcXX4LmJyYFKS9eI4MjA/Ad2brg1ECzBfUuOL8ijk1gxIaPSBjemON+rwRxON1D P2GCAMJCSWqSzEdvbkA5ISvJwuBA7UZ7MzQSPCRC2kwi7w3Oe6NjKkU+YVKyyV+ch2 l64AgbRKkRvTA== Message-ID: Date: Mon, 11 May 2026 14:47:57 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: "alloc_tag was not set" when running mm/ksft_hmm.sh To: Zenghui Yu Cc: Zenghui Yu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, jgg@ziepe.ca, leon@kernel.org, Andrew Morton , ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, Alistair Popple References: <10e4565a-b416-45d9-a8b0-cd32532b2630@kernel.org> <2b46241c-158b-c9dd-9b81-a98366b2c9fb@huawei.com> 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: <2b46241c-158b-c9dd-9b81-a98366b2c9fb@huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 29FB6A000C X-Stat-Signature: 9jaw5z8h1b4rde8t6ooayuqyf9cjfh6s X-Rspam-User: X-HE-Tag: 1778503682-72673 X-HE-Meta: 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 1BRtYuPA wrWR3M8pSNZDdtQKJxjO1dY3qWeBsxzXGKneWXBcGf7qyxo75pus0lkSMGDvsd2VYEtAnSIU2fCJ5SBElbWkx0ZBJIrutAQcprLwc6/75olFWeVEsCp1cHFzlcPK2AqCmSdbPCDfjmfvy4ixUrU/LZZJfPwXTpG+xu+CWWIDXvEliuTQSUus8NBAo+9cQYRD2gwS1qkD0DZB4xSNmeQteJGBsEYaCz+gby6WwCOYoEPeeHXTwEJGnMTmH8P1K5mnehNX1CITg/9VrpKC5f9M2NZjyZt3ZtdlsvqoA1RTefCKrf94hNcQxEqisk66dQcS3n+N6843Kw0vX/ZenROwKRLy9tMnhZborwEIjGKlqmu0vdFE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/11/26 14:19, Zenghui Yu wrote: > On 2026/5/8 19:53, David Hildenbrand (Arm) wrote: >> On 5/6/26 17:42, Zenghui Yu wrote: >>> Hi all, >>> >>> Running mm/ksft_hmm.sh triggers the following splat: >>> >>> ------------[ cut here ]------------ >>> alloc_tag was not set >>> WARNING: ./include/linux/alloc_tag.h:164 at ___free_pages+0x2a0/0x2d0, >>> CPU#5: hmm-tests/2020 >>> Modules linked in: test_hmm rfkill drm backlight fuse >>> CPU: 5 UID: 0 PID: 2020 Comm: hmm-tests Kdump: loaded Not tainted >>> 7.1.0-rc2-00099-gadc1e5c6203c-dirty #285 PREEMPT >>> Hardware name: QEMU QEMU Virtual Machine, BIOS >>> edk2-stable202408-prebuilt.qemu.org 08/13/2024 >>> pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) >>> pc : ___free_pages+0x2a0/0x2d0 >>> lr : ___free_pages+0x2a0/0x2d0 >>> sp : ffff80008345b530 >>> x29: ffff80008345b530 x28: ffff80008345b700 x27: ffffffffbfff8040 >>> x26: ffff0000c41cb360 x25: ffff0000c0c64008 x24: ffff800081aae400 >>> x23: 05ffff0000000200 x22: 0000000000000000 x21: 0000000000000000 >>> x20: fffffdffc5f20040 x19: 0000000000000000 x18: fffffffffffe7c78 >>> x17: 0000000000000000 x16: 0000000000000000 x15: fffffffffffe7c98 >>> x14: 00000000000001d1 x13: ffff8000818f3d58 x12: 0000000000000573 >>> x11: fffffffffffe7c98 x10: ffff80008194bd58 x9 : 3ffffffffffff000 >>> x8 : ffff8000818f3d58 x7 : ffff80008194bd58 x6 : 0000000000000000 >>> x5 : ffff0001fedb1088 x4 : 0000000000000001 x3 : 0000000000000000 >>> x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0000c7f58000 >>> Call trace: >>> ___free_pages+0x2a0/0x2d0 (P) >>> __free_pages+0x14/0x20 >>> dmirror_devmem_free+0x13c/0x158 [test_hmm] >>> free_zone_device_folio+0x144/0x1e4 >>> __folio_put+0x124/0x130 >>> free_folio_and_swap_cache+0xa8/0xcc >>> __folio_split+0x664/0x7fc >>> split_folio_to_list+0x50/0x5c >>> migrate_vma_split_folio+0x13c/0x25c >>> migrate_vma_collect_pmd+0xed4/0xf68 >>> walk_pgd_range+0x598/0x9a0 >>> __walk_page_range+0x90/0x1a0 >>> walk_page_range_mm_unsafe+0x194/0x20c >>> walk_page_range+0x20/0x2c >>> migrate_vma_setup+0x18c/0x224 >>> dmirror_devmem_fault+0x188/0x2b8 [test_hmm] >>> do_swap_page+0x1458/0x185c >>> __handle_mm_fault+0x85c/0x1ba0 >>> handle_mm_fault+0xb0/0x290 >>> do_page_fault+0x1f8/0x6f8 >>> do_translation_fault+0x60/0x6c >>> do_mem_abort+0x44/0x94 >>> el0_da+0x30/0xdc >>> el0t_64_sync_handler+0xd0/0xe4 >>> el0t_64_sync+0x198/0x19c >>> ---[ end trace 0000000000000000 ]--- >>> lib/test_hmm.c:705 module test_hmm func:dmirror_devmem_alloc_page has >>> 16744448 allocated at module unload >>> >>> >>> It was tested on kernel built with arm64's virt.config and >>> >>> +CONFIG_ZONE_DEVICE=y >>> +CONFIG_DEVICE_PRIVATE=y >>> +CONFIG_TEST_HMM=m >>> +CONFIG_MEM_ALLOC_PROFILING=y >>> +CONFIG_MEM_ALLOC_PROFILING_DEBUG=y >> >> I assume there is a weird interaction between alloc tags and simulated >> ZONE_DEVICE memory in test_hmm.c > > FYI this can be reproduced by running the migrate_partial_unmap_fault > test case. > > TEST_F(hmm, migrate_partial_unmap_fault) > { > buffer->mirror = malloc(TWOMEG); > buffer->ptr = map; // points to a THP > > /* Initialize buffer in system memory. */ > for (i = 0, ptr = buffer->ptr; i < TWOMEG / sizeof(*ptr); ++i) > ptr[i] = i; > > ret = hmm_migrate_sys_to_dev(self->fd, buffer, npages); > > munmap(buffer->ptr, ONEMEG); > > /* Fault pages back to system memory and check them. */ > for (i = 0, ptr = buffer->ptr; i < TWOMEG / sizeof(*ptr); ++i) > if (i * sizeof(int) < 0 || > i * sizeof(int) >= ONEMEG) > ASSERT_EQ(ptr[i], i); // triggers a fault -> > > > dmirror_devmem_fault() > migrate_vma_setup() > migrate_vma_collect_pmd() > // !pte_present(pte) && folio_test_large(folio) > migrate_vma_split_folio() > split_folio() > [...] > > __folio_split() { > unmap_folio(); > > __folio_freeze_and_split_unmapped() { > __split_unmapped_folio(); > > for (...) { > zone_device_private_split_cb(.., new_folio); > // -> dmirror_devmem_folio_split() which doesn't > // set alloc tag for the backing system memory > // page being split, i.e., rpage_tail > } > > zone_device_private_split_cb(.., NULL); > } > > remap_page(); > > for (...) > free_folio_and_swap_cache(new_folio); > // -> dmirror_devmem_free()/__free_page() which warns if > // the page being freed doesn't have alloc tag set, in > // alloc_tag_sub_check(). > } > > The WARN disappears with the following diff. But I'm not sure if I've > missed more important points (which is likely to happen ;-) ). > > diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c > index ed1bdcf1f8ab..eefa2a739917 100644 > --- a/lib/alloc_tag.c > +++ b/lib/alloc_tag.c > @@ -191,6 +191,7 @@ void pgalloc_tag_split(struct folio *folio, int > old_order, int new_order) > } > } > } > +EXPORT_SYMBOL(pgalloc_tag_split); > > void pgalloc_tag_swap(struct folio *new, struct folio *old) > { > diff --git a/lib/test_hmm.c b/lib/test_hmm.c > index 213504915737..3bec51828916 100644 > --- a/lib/test_hmm.c > +++ b/lib/test_hmm.c > @@ -1713,6 +1713,7 @@ static void dmirror_devmem_folio_split(struct > folio *head, struct folio *tail) > rfolio = page_folio(rpage); > > if (tail == NULL) { > + pgalloc_tag_split(rfolio, folio_order(rfolio), 0); > folio_reset_order(rfolio); > rfolio->mapping = NULL; > folio_set_count(rfolio, 1); > > Thanks, > Zenghui zone_device_private_split_cb(), that ends up calling ->folio_split(). We do have a call to pgalloc_tag_split() in __split_unmapped_folio(), invoked in __folio_freeze_and_split_unmapped() before calling zone_device_private_split_cb() when iterating the folios. The zone_device_private_split_cb(folio, NULL); is then called on the first folio after looping over the other (new) folios. I would assume that __folio_freeze_and_split_unmapped() would already do the right thing? Maybe the issue is the hard-coded folio_reset_order() in dmirror_devmem_folio_split(), where we seem to assume that we split to an order-0 folio? -- Cheers, David