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[2003:cb:c743:5100:93b1:f654:ad11:cd81]) by smtp.gmail.com with ESMTPSA id b5-20020a5d4d85000000b00324853fc8adsm1843327wru.104.2023.10.17.07.53.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Oct 2023 07:53:47 -0700 (PDT) Message-ID: <17a890e2-a87b-446e-9088-bd608504378b@redhat.com> Date: Tue, 17 Oct 2023 16:53:46 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/sparsemem: fix race in accessing memory_section->usage To: Charan Teja Kalla , Pavan Kondeti Cc: akpm@linux-foundation.org, osalvador@suse.de, dan.j.williams@intel.com, vbabka@suse.cz, mgorman@techsingularity.net, aneesh.kumar@linux.ibm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1697202267-23600-1-git-send-email-quic_charante@quicinc.com> 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: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 070161C000D X-Stat-Signature: rbpjtegosq7p1fhyodcy5qr5crbior6p X-Rspam-User: X-HE-Tag: 1697554440-508775 X-HE-Meta: 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 dBpsD58Y 6qFw0mE7FYC/lbNEUZgdhPMS4Y9oYLzFIzaKoyiCgOn1dis3YvyrGccKCcpfVJTzf5H3uATGpc5NfM2t/eQTvw9wQxWzJ3ugxaoKVsX8bUH69uykRnTu2tybUtHSN4RRNKKsxg/ED9tyzv74SHJEQ8X6DwoDu0aBpnw3gvcRj3HUbGcbd6wVa2B/iljui1ZC3mmnGZA2jsr9azqEDUWwDXkSjZbLwkseqfEfGKhsZ3B4fnYjceSY0r4TPAAvn7mO56RdUW8SidbFlsWajHQtoEIscuVYVEsDHZGqokNxAz2xjPejRXHiqu00j8kByxxA1huYR08msZHbomh4H0El9gMnt+GameaUaWDXAhG1sJJim4car31OAn+aB/e+IXdc3zzqmxNogDoKsYJaUvVpRG+GSPoWL3c5bBtLiyO/KDx2IqbNIBR7d0Yteg8SkXpeT5jbbBRES4YvYW+vpDPTrUveJmA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000031, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 17.10.23 16:10, Charan Teja Kalla wrote: > Thanks Pavan!! > > On 10/16/2023 4:03 PM, Pavan Kondeti wrote: >>> Fix this issue by the below steps: >>> a) Clear SECTION_HAS_MEM_MAP before freeing the ->usage. >>> b) RCU protected read side critical section will either return NULL when >>> SECTION_HAS_MEM_MAP is cleared or can successfully access ->usage. >>> c) Synchronize the rcu on the write side and free the ->usage. No >>> attempt will be made to access ->usage after this as the >>> SECTION_HAS_MEM_MAP is cleared thus valid_section() return false. >>> >>> Since the section_deactivate() is a rare operation and will come in the >>> hot remove path, impact of synchronize_rcu() should be negligble. >> struct mem_section_usage has other field like pageblock_flags. Do we >> need to protect its readers with RCU? Also can we annotate usage field >> in struct mem_section with __rcu and use RCU accessors like >> rcu_dereference() while using memsection::usage field? > > Good question about the pageblock_flags!! I think we rely on the > get_pageblock_bitmap() to read the ms->usage->pageblock_flags by passing > struct page*. > > 1) All the functions that I have come across calling > get_pageblock_bitmap()/get_pfnblock_flags_mask() passing the page* which > it get from buddy. I think we are safe here as the device pages(from > which the problem is coming will never be onlined/added to buddy) > > 2) There are functions in compaction which directly operate on the pfn's > through pfn_to_online_page(). As for device pages, it is going to return > NULL, I think we are safe here too. > > 3) alloc_contig_range() which also operate on the pfn's directly, and > TMK, we will not pass the [start , end) values of this function to > contains the hole/offlined pages. I think we are safe here too. > > May be David/other reviewers can help in commenting if there are some > mistakes above. Sound reasonable to me; most PFN walkers shouldn't deal with pageblock flags. alloc_contig_range() is certainly interesting, I suspect it's fine but we better double-check. -- Cheers, David / dhildenb