From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 28C1A3D6CD3 for ; Mon, 11 May 2026 12:48:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778503682; cv=none; b=Ywh8bKNef9bq6fP7uYJMqXN1Oqdi5KomGeilHlR0guckyEI00oJ7LAWxB/WXpYFdrgUaLLAPV6vF85sRDUZt5KTejAz3qZPnm4XaR3XEKS6/ndBtVaCY6H2bNTmfSou/mwunz5GY3AXCBD7XYEHV05uxky+BwZ7mcK/AKVxFdN8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778503682; c=relaxed/simple; bh=xjCTB5ceIJr0tNHKjbbLsapZ9izKDwKmO+QdBIUbBGU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qKmkkQFGKxXx8neveYhxzPIyCvvAl877IRjWuHMNzz6yKDne7RRYmRL5rHagThyUCzvikxu/8ZWFhdzeWU57Sg0YvJDAxa37Q7ng31QEf5GjGEk0wJOorgh+qqu7DX3JYu/VuGfTJiBHqLSJajD74xOD1DS+0DUWe4uQ8qZyWCQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RxuFM0wY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RxuFM0wY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B7E77C2BD00; Mon, 11 May 2026 12:47:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778503681; bh=xjCTB5ceIJr0tNHKjbbLsapZ9izKDwKmO+QdBIUbBGU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; 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 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: "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; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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