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[2003:cb:c738:3100:8133:26cf:7877:94aa]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-437c16640bcsm8024435e9.1.2025.01.14.01.40.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Jan 2025 01:40:29 -0800 (PST) Message-ID: Date: Tue, 14 Jan 2025 10:40:27 +0100 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: [PATCH 2/2] hwpoison, memory_hotplug: lock folio before unmap hwpoisoned folio To: mawupeng , akpm@linux-foundation.org, osalvador@suse.de, nao.horiguchi@gmail.com, linmiaohe@huawei.com, mhocko@suse.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250113082718.1872494-1-mawupeng1@huawei.com> <20250113082718.1872494-3-mawupeng1@huawei.com> <65b1122c-f107-44af-8c9d-726a38d04c24@huawei.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <65b1122c-f107-44af-8c9d-726a38d04c24@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 14.01.25 10:08, mawupeng wrote: > > > On 2025/1/13 20:35, David Hildenbrand wrote: >> On 13.01.25 09:27, Wupeng Ma wrote: >>> From: Ma Wupeng >>> >>> Commit b15c87263a69 ("hwpoison, memory_hotplug: allow hwpoisoned pages to >>> be offlined) add page poison checks in do_migrate_range in order to make >>> offline hwpoisoned page possible by introducing isolate_lru_page and >>> try_to_unmap for hwpoisoned page. However folio lock must be held before >>> calling try_to_unmap. Add it to fix this problem. >>> >>> Waring will be produced if filio is not locked during unmap: >>> >>>    ------------[ cut here ]------------ >>>    kernel BUG at ./include/linux/swapops.h:400! >>>    Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP >>>    Modules linked in: >>>    CPU: 4 UID: 0 PID: 411 Comm: bash Tainted: G        W          6.13.0-rc1-00016-g3c434c7ee82a-dirty #41 >>>    Tainted: [W]=WARN >>>    Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015 >>>    pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) >>>    pc : try_to_unmap_one+0xb08/0xd3c >>>    lr : try_to_unmap_one+0x3dc/0xd3c >>>    Call trace: >>>     try_to_unmap_one+0xb08/0xd3c (P) >>>     try_to_unmap_one+0x3dc/0xd3c (L) >>>     rmap_walk_anon+0xdc/0x1f8 >>>     rmap_walk+0x3c/0x58 >>>     try_to_unmap+0x88/0x90 >>>     unmap_poisoned_folio+0x30/0xa8 >>>     do_migrate_range+0x4a0/0x568 >>>     offline_pages+0x5a4/0x670 >>>     memory_block_action+0x17c/0x374 >>>     memory_subsys_offline+0x3c/0x78 >>>     device_offline+0xa4/0xd0 >>>     state_store+0x8c/0xf0 >>>     dev_attr_store+0x18/0x2c >>>     sysfs_kf_write+0x44/0x54 >>>     kernfs_fop_write_iter+0x118/0x1a8 >>>     vfs_write+0x3a8/0x4bc >>>     ksys_write+0x6c/0xf8 >>>     __arm64_sys_write+0x1c/0x28 >>>     invoke_syscall+0x44/0x100 >>>     el0_svc_common.constprop.0+0x40/0xe0 >>>     do_el0_svc+0x1c/0x28 >>>     el0_svc+0x30/0xd0 >>>     el0t_64_sync_handler+0xc8/0xcc >>>     el0t_64_sync+0x198/0x19c >>>    Code: f9407be0 b5fff320 d4210000 17ffff97 (d4210000) >>>    ---[ end trace 0000000000000000 ]--- >>> >>> Fixes: b15c87263a69 ("hwpoison, memory_hotplug: allow hwpoisoned pages to be offlined") >>> Signed-off-by: Ma Wupeng >>> --- >>>   mm/memory_hotplug.c | 6 +++++- >>>   1 file changed, 5 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index 330668d37e44..9bedecfc3577 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -1805,8 +1805,12 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn) >>>               (folio_test_large(folio) && folio_test_has_hwpoisoned(folio))) { >>>               if (WARN_ON(folio_test_lru(folio))) >>>                   folio_isolate_lru(folio); >>> -            if (folio_mapped(folio)) >>> +            if (folio_mapped(folio)) { >>> +                folio_lock(folio); >>>                   unmap_poisoned_folio(folio, TTU_IGNORE_MLOCK | TTU_HWPOISON); >>> +                folio_unlock(folio); >>> +            } >> >> The comment above says "have elevated reference counts", but I I wonder if this code could race with un-poisoning (although probably a rare event). >> >> >> If there is an elevated reference already, why not move that chunk after the folio_try_get() and just drop the comment that describes the implied magic? >> >> I mean, migration of hwpoison is dangerous either way, so that's not the biggest problem I guess :) > > AFAICT during memory_failure, the refcount will not be cleared for poisoned page in order to keep it away from free buddy pages. > So move that chunk after the folio_try_get() do seems nice and poisoned free pages do seems weird to me. If the "free" poisoned pages have a raised refcount, folio_try_get() would be able to grab them to essentially skip them (not mapped). If the "free" poisoned pages don't have a raised refcount (impossible right now IIRC), folio_try_get() would skip, them, which would be the right thing to do. So I think that should work. -- Cheers, David / dhildenb