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(p200300d82f22060053c7df437dc3ae39.dip0.t-ipconnect.de. [2003:d8:2f22:600:53c7:df43:7dc3:ae39]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45a221bbadfsm125147675e9.0.2025.08.18.02.44.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Aug 2025 02:44:18 -0700 (PDT) Message-ID: <3970cd97-2e9e-403f-867a-3addfbe399dc@redhat.com> Date: Mon, 18 Aug 2025 11:44:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/6] Remove XA_ZERO from error recovery of To: "Liam R. Howlett" , Lorenzo Stoakes Cc: maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Andrew Morton , Jann Horn , Pedro Falcato , Charan Teja Kalla , shikemeng@huaweicloud.com, kasong@tencent.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, chrisl@kernel.org, Matthew Wilcox References: <20250815191031.3769540-1-Liam.Howlett@oracle.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250815191031.3769540-1-Liam.Howlett@oracle.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: _GhCGK2Ln9AP0I1cpNsUmkhQnrCN3kb_gSsJfNTBUbk_1755510259 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: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 6899720004 X-Stat-Signature: pk9co39y45u4f9iwkuc9r3pj4g64mkkx X-HE-Tag: 1755510263-652262 X-HE-Meta: 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 wfVv6qz0 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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 15.08.25 21:10, Liam R. Howlett wrote: > Before you read on, please take a moment to acknowledge that David > Hildenbrand asked for this, so I'm blaming mostly him :) :) > > It is possible that the dup_mmap() call fails on allocating or setting > up a vma after the maple tree of the oldmm is copied. Today, that > failure point is marked by inserting an XA_ZERO entry over the failure > point so that the exact location does not need to be communicated > through to exit_mmap(). > > However, a race exists in the tear down process because the dup_mmap() > drops the mmap lock before exit_mmap() can remove the partially set up > vma tree. This means that other tasks may get to the mm tree and find > the invalid vma pointer (since it's an XA_ZERO entry), even though the > mm is marked as MMF_OOM_SKIP and MMF_UNSTABLE. > > To remove the race fully, the tree must be cleaned up before dropping > the lock. This is accomplished by extracting the vma cleanup in > exit_mmap() and changing the required functions to pass through the vma > search limit. > > This does run the risk of increasing the possibility of finding no vmas > (which is already possible!) in code this isn't careful. Right, it would also happen if __mt_dup() fails I guess. > > The passing of so many limits and variables was such a mess when the > dup_mmap() was introduced that it was avoided in favour of the XA_ZERO > entry marker, but since the swap case was the second time we've hit > cases of walking an almost-dead mm, here's the alternative to checking > MMF_UNSTABLE before wandering into other mm structs. Changes look fairly small and reasonable, so I really like this. I agree with Jann that doing a partial teardown might be even better, but code-wise I suspect it might end up with a lot more churn and weird allocation-corner-cases to handle. -- Cheers David / dhildenb