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Wed, 26 Mar 2025 05:53:53 -0700 (PDT) X-Google-Smtp-Source: AGHT+IE08r2oP2q1wjXgv2UW+Hz/KpEjdw6OIzNgcAqvmcn1/G8sUsEHYLVYKNY4QZQTlPmx7b1xJA== X-Received: by 2002:a05:622a:5514:b0:476:8d14:6e7 with SMTP id d75a77b69052e-4771de15a3dmr349026071cf.33.1742993633293; Wed, 26 Mar 2025 05:53:53 -0700 (PDT) Received: from [172.20.3.205] ([99.209.85.25]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4771d15a10esm71320841cf.13.2025.03.26.05.53.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Mar 2025 05:53:52 -0700 (PDT) Message-ID: Date: Wed, 26 Mar 2025 13:53:51 +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-Queue-Id: 680F7C0022 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: sjupmhgd1iiccz1r13tb9guzhr7ttwh7 X-HE-Tag: 1742993636-536516 X-HE-Meta: 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 B/2NAWR9 7tsmcXC6XRLXwwosiqxuILKHG4hu89A6Tka6BN1xBFmeswS7viVjgPRLkxqkgkA9kZ26esolZ2U4n5Bdw/xQUnmC+6XE8M1P/p0mQggbmE1aAkgZDZOCCFndVaCcnZvEg6PwivOeVVDJK6GbARDregOqZmVmGR4rq2FIPYSoiEKA0SELQygf/6mJcHLgLOSsD6YcRb1JSRTzpfx/TUwX7DSCn6ENhuhEvW9WgQ3Z9gixVjmSvzGaTd5WQayt89kZ/YvBdsUM0kIIEOt0Yo3EnCbVKXTG5XWPXI8l7T+3Px639ChPIavd2Zb3QAjNQjt4u4K85a9WcevzipPOen8mhu4HgT5LhflSvG8uf2d1ucZ8iIiNvV/OVYq3XH9KrTZ989HGm6jAFPl2lLgVByTYCJ+4uS2TBvwkzdjSRlbzrJjw30EhBAdScY8DZ5QSwTaP+FT+XuuOBsxIuXU/+nbuXdm6MVOTnYaW7wujM+Y98VOR+PGR3N2fSpqie4l2w3uPK4KhuAPyn4Xqlk+p4EygMCSln+dYsU1mNVG86PzKhgcEohprzWmUFin+iQvypRtKU+x++lmDqRdnR+xY9TO4Cl+xWKy1FGoCF+uNdw0Tqz5OYU1A= 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 26.03.25 03:40, Jinjiang Tu wrote: > > 在 2025/3/26 3:05, David Hildenbrand 写道: >> 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. > > commit 8135d8926c08 adds PageTransHuge() call, which may lead to VM_BUG_ON if the page is tail page. Right; we check for PageHuge before that. > Before it, for hugetlb, PageHuge()、compound_head() and compound_order() are called before getting > page ref, PageHuge()、compound_head() allows to pass a tail page, compound_order() will not trigger > trigger VM_BUG_ON for tail page, and only lead to reading garbage data, leading to fail offline, but We will retry as documented, so offlining should not fail. > it will not trigger any VM_BUG_ON. So I think 8135d8926c08 is the introducing commit. Not for the hugetlb issue you describe I assume. That should be caused by commit b62b51d2d1593e6590669e781768c3c5a7394eb5 Author: Kefeng Wang Date: Tue Aug 27 19:47:24 2024 +0800 mm: memory_hotplug: remove head variable in do_migrate_range() Patch series "mm: memory_hotplug: improve do_migrate_range()", v3. So probably we should have both commits as Fixes (one for the hugetlb path, one for the THP path) -- Cheers, David / dhildenb