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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-427d2b1825asm14728955e9.15.2024.07.18.07.02.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Jul 2024 07:02:56 -0700 (PDT) Message-ID: Date: Thu, 18 Jul 2024 16:02:55 +0200 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 RFC] mm/page_alloc: Fix pcp->count race between drain_pages_zone() vs __rmqueue_pcplist() To: "Vlastimil Babka (SUSE)" , Li Zhijian , linux-mm@kvack.org Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Yasunori Gotou , Yao Xingtao , Lucas Stach References: <20240716073929.843277-1-lizhijian@fujitsu.com> <6f2151a9-da23-4917-b985-8de6b0852e37@kernel.org> Content-Language: en-US From: David Hildenbrand 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: <6f2151a9-da23-4917-b985-8de6b0852e37@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 18.07.24 13:16, Vlastimil Babka (SUSE) wrote: > On 7/16/24 9:39 AM, Li Zhijian wrote: >> It's expected that no page should be left in pcp_list after calling >> zone_pcp_disable() in offline_pages(). Previously, it's observed that >> offline_pages() gets stuck [1] due to some pages remaining in pcp_list. >> >> Cause: >> There is a race condition between drain_pages_zone() and __rmqueue_pcplist() >> involving the pcp->count variable. See below scenario: >> >> CPU0 CPU1 >> ---------------- --------------- >> spin_lock(&pcp->lock); >> __rmqueue_pcplist() { >> zone_pcp_disable() { >> /* list is empty */ >> if (list_empty(list)) { >> /* add pages to pcp_list */ >> alloced = rmqueue_bulk() >> mutex_lock(&pcp_batch_high_lock) >> ... >> __drain_all_pages() { >> drain_pages_zone() { >> /* read pcp->count, it's 0 here */ >> count = READ_ONCE(pcp->count) >> /* 0 means nothing to drain */ >> /* update pcp->count */ >> pcp->count += alloced << order; >> ... >> ... >> spin_unlock(&pcp->lock); >> >> In this case, after calling zone_pcp_disable() though, there are still some >> pages in pcp_list. And these pages in pcp_list are neither movable nor >> isolated, offline_pages() gets stuck as a result. >> >> Solution: >> Expand the scope of the pcp->lock to also protect pcp->count in >> drain_pages_zone(), ensuring no pages are left in the pcp list. >> >> [1] https://lore.kernel.org/linux-mm/6a07125f-e720-404c-b2f9-e55f3f166e85@fujitsu.com/ >> >> Cc: David Hildenbrand >> Reported-by: Yao Xingtao >> Signed-off-by: Li Zhijian >> --- >> mm/page_alloc.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 9ecf99190ea2..1780df31d5f5 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -2323,16 +2323,17 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp) >> static void drain_pages_zone(unsigned int cpu, struct zone *zone) >> { >> struct per_cpu_pages *pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu); >> - int count = READ_ONCE(pcp->count); >> + int count; >> >> + spin_lock(&pcp->lock); >> + count = pcp->count; >> while (count) { >> int to_drain = min(count, pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX); >> count -= to_drain; >> >> - spin_lock(&pcp->lock); >> free_pcppages_bulk(zone, to_drain, pcp, 0); >> - spin_unlock(&pcp->lock); >> } >> + spin_unlock(&pcp->lock); > > This way seems to be partially going against the purpose of 55f77df7d715 > ("mm: page_alloc: control latency caused by zone PCP draining") - the zone > lock hold time will still be limited by the batch, but not the pcp lock > time. It should still be possible to relock between the iterations? To > prevent the race I think the main part is determining pcp->count under the > lock, but release/retake should still be ok if the pcp->count is reread > after relocking. Agreed, had the smame thing in mind when skimming over this patch. @Li, with this patch the problems you have been seeing are fully resolved, correct? -- Cheers, David / dhildenb