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[2003:cb:c737:1f00:94ff:246b:30d0:686b]) by smtp.gmail.com with ESMTPSA id z7-20020a2e8e87000000b002d45ad8efdesm1408810ljk.106.2024.03.18.03.54.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Mar 2024 03:54:31 -0700 (PDT) Message-ID: <8819b03d-7715-4159-863d-f15e94adcc29@redhat.com> Date: Mon, 18 Mar 2024 11:54:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/ksm: fix ksm exec support for prctl To: Jinjiang Tu , akpm@linux-foundation.org, shr@devkernel.io, hannes@cmpxchg.org, riel@surriel.com, wangkefeng.wang@huawei.com, sunnanyong@huawei.com, linux-mm@kvack.org References: <20240318090441.179486-1-tujinjiang@huawei.com> <527963a1-e7e5-78ab-99dd-2677de980eed@huawei.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: <527963a1-e7e5-78ab-99dd-2677de980eed@huawei.com> 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: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A33F810000C X-Stat-Signature: zwbodeusw4tk6kdsiryknh86e1g7smdn X-Rspam-User: X-HE-Tag: 1710759275-393264 X-HE-Meta: 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 Tl1m86U+ SEG0d6m06xT7DmFvYM7TCtLQO+3j1L9nR5PSHz3X3vsCKd4UDUH8OyJbXrFcmb8en6UVDY+fxf43CGjePbojqzyMi9JgrHpFikKMwGOkMUL3BlKLjP+XXBJClhyC7hjJIMzcpRbbNnlbvz4mYMNn89p332/rLyp5XmMyi 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: >>>   +static inline int ksm_execve(struct mm_struct *mm) >>> +{ >>> +    if (test_bit(MMF_VM_MERGE_ANY, &mm->flags)) >>> +        return __ksm_enter(mm); >> >> As soon as we did the __ksm_enter(), we have to set MMF_VM_MERGEABLE. >> I don't think it would be set right now, because: >> >> mm_alloc()->mm_init() will initialize the flags using >> >>     mm->flags = mmf_init_flags(current->mm->flags); >> >> Whereby MMF_INIT_MASK contains only MMF_VM_MERGE_ANY_MASK. >> >> >> So we likely need a set_bit(MMF_VM_MERGEABLE, &mm->flags) here as >> well. Otherwise ksm_exit() wouldn't clean up, and we might call >> __ksm_enter() twice. > > __ksm_enter() will set MMF_VM_MERGEABLE when it succeeds. > Ah, indeed! >> >> >> And now I wonder, when would be the right point to call __ksm_enter(). >> >> __mmput() calls ksm_exit(). But for example, if __bprm_mm_init() fails >> after __ksm_enter(), we will only call mmdrop(), not cleaning up ... >> so that looks wrong. > Yes, I forgot cleanup in error path. ksm_exit() should be called when > __bprm_mm_init() fails after __ksm_enter(). >> >> We would have to make sure we call __ksm_enter() only once we know >> that callers will call mm_put(). that is the case once we return from >> bprm_mm_init() with success. >> >> Maybe move the ksm_execve() to bprm_mm_init(), adding a comment that >> cleanup will only happen during mm_put(), so it's harder to mess up in >> the future? >> > __ksm_enter() should be called under mmap write lock to avoid race with > ksmd. So we can't move ksm_execve() to bprm_mm_init(). Makes sense. We have to be careful that this won't silently break in the future. Better add some comment as well. -- Cheers, David / dhildenb