From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (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 54A422D7814 for ; Mon, 11 May 2026 16:38:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778517541; cv=none; b=b+dgPS92UNOaZUK0z5OZw49FVvmackAmc4QEOZ4sWYMjLPgufnS3o2HM4xRm775RG5Zzs2xhe3htfyZX6Y8YDc0qf/kyKPMgG6gXzX4BwarXhHg8q14EQaewqO242nHHekjt9QY15XBjWnRc2r7LV/2jIHikWN7WHb39NrxSfRQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778517541; c=relaxed/simple; bh=gIX6NMvbqt04gxx75FxaAdeG3wj82+k2cAyNgkJXVxQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OSDnxiG9BTGC8qIHzuT0/kqBNCSEdEfPxe49LOfMUouBnqQ11nUBHcuQYnNI5v/NiY3Iv9psXJf5CXARjCjhmWKljBmbp16pA13xV4l3IEYHKWn9Wu24sxvgFECWgZGLUoJ9u2Lod28U2355IyLa/JkUZO4TQpO1UX0iOmgZmdw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=HPVz3qKC; arc=none smtp.client-ip=91.218.175.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="HPVz3qKC" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1778517536; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=atbYDvhBZSt0K6jPPBLuz6AZnTDfzHuTJr9adJta60Q=; b=HPVz3qKC0mlPPZmmMKe3J4vbCgTMVfn2DcNZC1+M/f9M+SEXrcIhkEiCf/86dPHEUG1bkG tw5nAOI9f8c7aQL07C4voz1JGK6Na9VaUgsy/dxnWg9cvcDM5JaPxby/TlO12+j35TLXXP kkLSOyb06x2/9Z+05GuzavuU3UKCp24= Date: Tue, 12 May 2026 00:38:36 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: "alloc_tag was not set" when running mm/ksft_hmm.sh To: "David Hildenbrand (Arm)" 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> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Zenghui Yu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Hi David, On 5/11/26 8:47 PM, David Hildenbrand (Arm) wrote: > 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); > > > 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. If I read the code correctly, pgalloc_tag_split() in __split_unmapped_folio() deals with device private pages' alloc tag. But what alloc_tag_sub_check() warns on are real system memory pages (device page's backing page), which are allocated by dmirror_devmem_alloc_page()/folio_page(). static void dmirror_devmem_folio_split(struct folio *head, struct folio *tail) { struct page *rpage = BACKING_PAGE(folio_page(head, 0)); Thanks, Zenghui > 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? >