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Mon, 24 Mar 2025 06:44:54 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFaa5vTcpk1dptrvpVglVn+tgdqFBEZLPOM6+LsxtTu6lENWQxrF/qzKXLwqK2KfC5znJMAXA== X-Received: by 2002:a05:622a:59c5:b0:476:6f90:395e with SMTP id d75a77b69052e-4771dd94fcbmr209859731cf.21.1742823892259; Mon, 24 Mar 2025 06:44:52 -0700 (PDT) Received: from [172.22.33.10] ([99.209.85.25]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4771d15a2cesm47493991cf.10.2025.03.24.06.44.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Mar 2025 06:44:51 -0700 (PDT) Message-ID: <899807c3-931f-43e6-bf3e-188787a4205a@redhat.com> Date: Mon, 24 Mar 2025 14:44:50 +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> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Stat-Signature: p68dkcthwt4hpab1o8jm7zkh6tod79bx X-Rspam-User: X-Rspamd-Queue-Id: 0B83AA001A X-HE-Tag: 1742823896-666771 X-HE-Meta: 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 U4QK7Nvj 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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 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 .. We could similarly to dumping folios, snapshot them, so we can read stable data. -- Cheers, David / dhildenb