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Tue, 25 Mar 2025 12:05:52 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFupWAtbKpiZvvOfbbZq9GJdSDmQY7RKU2qwxmjnHUkIfvmGUNxIRGoVb5jLS6liSgyDaYMPg== X-Received: by 2002:a05:620a:269b:b0:7c5:6375:144c with SMTP id af79cd13be357-7c5ba15e475mr2801837085a.23.1742929552411; Tue, 25 Mar 2025 12:05:52 -0700 (PDT) Received: from [172.20.3.205] ([99.209.85.25]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c5b9348358sm672810285a.71.2025.03.25.12.05.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Mar 2025 12:05:51 -0700 (PDT) Message-ID: Date: Tue, 25 Mar 2025 20:05:50 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/memory_hotplug: fix call folio_test_large with tail page in do_migrate_range To: Jinjiang Tu , osalvador@suse.de, akpm@linux-foundation.org, nao.horiguchi@gmail.com, zi.yan@cs.rutgers.edu Cc: linux-mm@kvack.org, wangkefeng.wang@huawei.com, sunnanyong@huawei.com References: <20250324131750.1551884-1-tujinjiang@huawei.com> <899807c3-931f-43e6-bf3e-188787a4205a@redhat.com> <68ab727b-dc3d-327f-33b6-25bbfce8530e@huawei.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 6594D20014 X-Stat-Signature: in8muhhqk4w6m63si6i8m9u7e5nnygbo X-Rspam-User: X-HE-Tag: 1742929561-972826 X-HE-Meta: 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 zdVsCEWq 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 25.03.25 04:02, Jinjiang Tu wrote: > > 在 2025/3/24 21:44, David Hildenbrand 写道: >> On 24.03.25 14:17, Jinjiang Tu wrote: >>> We triggered the below BUG: >>> >>>   page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x2 >>> pfn:0x240402 >>>   head: order:9 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 >>> pincount:0 >>>   flags: 0x1ffffe0000000040(head|node=1|zone=3|lastcpupid=0x1ffff) >>>   page_type: f4(hugetlb) >>>   page dumped because: VM_BUG_ON_PAGE(page->compound_head & 1) >>>   ------------[ cut here ]------------ >>>   kernel BUG at ./include/linux/page-flags.h:310! >>>   Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP >>>   Modules linked in: >>>   CPU: 7 UID: 0 PID: 166 Comm: sh Not tainted 6.14.0-rc7-dirty #374 >>>   Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015 >>>   pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) >>>   pc : const_folio_flags+0x3c/0x58 >>>   lr : const_folio_flags+0x3c/0x58 >>>   Call trace: >>>    const_folio_flags+0x3c/0x58 (P) >>>    do_migrate_range+0x164/0x720 >>>    offline_pages+0x63c/0x6fc >>>    memory_subsys_offline+0x190/0x1f4 >>>    device_offline+0xc0/0x13c >>>    state_store+0x90/0xd8 >>>    dev_attr_store+0x18/0x2c >>>    sysfs_kf_write+0x44/0x54 >>>    kernfs_fop_write_iter+0x120/0x1cc >>>    vfs_write+0x240/0x378 >>>    ksys_write+0x70/0x108 >>>    __arm64_sys_write+0x1c/0x28 >>>    invoke_syscall+0x48/0x10c >>>    el0_svc_common.constprop.0+0x40/0xe0 >>> >>> When allocating a hugetlb folio, between the folio is taken from buddy >>> and prep_compound_page() is called, start_isolate_page_range() and >>> do_migrate_range() is called. When do_migrate_range() scans the head >>> page >>> of the hugetlb folio, the compound_head field isn't set, so scans the >>> tail page next. And at this time, the compound_head field of tail >>> page is >>> set, folio_test_large() is called by tail page, thus triggers >>> VM_BUG_ON(). >>> >>> To fix it, get folio refcount before calling folio_test_large(). >>> >>> Fixes: 8135d8926c08 ("mm: memory_hotplug: memory hotremove supports >>> thp migration") >>> Signed-off-by: Jinjiang Tu >>> --- >>>   mm/memory_hotplug.c | 12 +++--------- >>>   1 file changed, 3 insertions(+), 9 deletions(-) >>> >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index 16cf9e17077e..f600c26ce5de 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -1813,21 +1813,15 @@ static void do_migrate_range(unsigned long >>> start_pfn, unsigned long end_pfn) >>>           page = pfn_to_page(pfn); >>>           folio = page_folio(page); >>>   -        /* >>> -         * No reference or lock is held on the folio, so it might >>> -         * be modified concurrently (e.g. split).  As such, >>> -         * folio_nr_pages() may read garbage.  This is fine as the >>> outer >>> -         * loop will revisit the split folio later. >>> -         */ >>> -        if (folio_test_large(folio)) >>> -            pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1; >>> - >>>           if (!folio_try_get(folio)) >>>               continue; >>>             if (unlikely(page_folio(page) != folio)) >>>               goto put_folio; >>>   +        if (folio_test_large(folio)) >>> +            pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1; >> >> Moving that will not make it able to skip the large frozen >> (refcount==0, e.g., free hugetlb) folio in the continue/put_folio case >> above. Hmmmm .. > For free hugetlb, pfn is increased by 1 in each loop. This leads to skip > free hugetlb slower. Yes. But now I realize that we have the same issue with free buddy pages already (folio_try_get of each individual page :( ). >> >> We could similarly to dumping folios, snapshot them, so we can read >> stable data. > extract the code in __dump_page()? But snapshot may lead to > do_migrate_range() slower too. There is a patch series on the list to do that, but it might take a while to clean that up. Ideally, we'd also jump over free buddy pages. In the future we might have better ways to do that. I don't consider this change here really important, but if all it affects is free hugetlb folios, it's not really worth it to have this code around. Acked-by: David Hildenbrand But: I suspect 8135d8926c08 is not the introducing commit. Please re-verify. We should not CC stable. -- Cheers, David / dhildenb