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[2003:cb:c705:fb00:4bb9:5362:8a63:a97d]) by smtp.gmail.com with ESMTPSA id l3-20020adff483000000b0033719111458sm992009wro.36.2024.01.05.00.56.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Jan 2024 00:56:30 -0800 (PST) Message-ID: <556f8a4f-c739-41e0-85ec-643a0b32a2ce@redhat.com> Date: Fri, 5 Jan 2024 09:56:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity_checks To: Ryan Roberts , Yin Fengwei , syzbot , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, Matthew Wilcox References: <000000000000014174060e09316e@google.com> <3feecbd6-b3bd-440c-a4f9-2a7dba3ff8f1@intel.com> <36ace74a-1de7-4224-8bc1-7f487764f6e2@redhat.com> <8bc02927-a0f0-490a-a014-0e100d30ffe4@intel.com> <1eb61435-c89c-4ca1-b1b6-aa00b3478cd2@arm.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: <1eb61435-c89c-4ca1-b1b6-aa00b3478cd2@arm.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-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B5A511C0005 X-Stat-Signature: 6fuistmk56aagapbzxkfekxksq83kpjn X-HE-Tag: 1704444994-952171 X-HE-Meta: U2FsdGVkX19n1RXPM9xhOm9+dsx7XDUCICZHDFxIIx5HR6rRqUo47XvxL78hxym5+jDXXrB9DhieqGjFDb8gfg/T71ToqOX8nr14ZXaQTIY29GJEDN4FkyzSTTEfYv31QsZVhYcCRyHq2xZ0Ut/u6zuPfM9dNjuDT8gcQqNiW4Xg0WythWh5jdbhjyqFri78GdRu5YY6+EYqpFiUdvikYzyPa0psIOGgvCxhwBoW6YWSIY2xeBGopEqDl3Okqnx7bdgY2zljueDHmIB3ZU8obewT+tqN8NIER5WYNXYTFECYlu+r83fTa11eJQai9/ghVBFEmsjBCZ5TXkoUKiV39Bhmcb3IGeIve90n25F8SQ5c1jLI+VJymaWAT/QC0KsskqWqqKUILYlD+4olo6xmkve0TaINVt0/X7zwtCIL10rSILsuV0hvGrsYEl+/dtMJbFg9eNv5LYKriXplOqTAPDZPaCKcWJHUVW//BvpjpkItPI9u3h/TqAHwswOkwjjCTUiw1lGIFYin1RphVhmYmUKwljWLPhnmFpDwlYkvvRYYSjqg7PJMH7G5VIaYnRR8Lzx2KpiGjN2Kz+6G2mM1LUzU4bP6wVCMZQvm3X2qGG4Y3rqcSG2M0hEv7SLjJFkfNTfPYSOzLl2NXfJcj2YhdepWlW5wOT4S2cQwR0tAkHdaBKxi05DHc8yM8PazA5vHc+NRsxOsF6tdxSAJMJ1sZyc35FEgF6jeSpNhwZs3t8WyiUYtkQExyht14QP6Cyek6KEL0v1zLat1HvGmx4+NZiwU++KWuGvhBBGcmMjhBo/A72PJas3VOKubPiMiG3sMnCqNSsUwT2KhKNE5Yol8HTGMpxrkozT8lZRRqU+qVwQMInpw/83wkkGjyzRdJsTvmJyVch2C0oru1ZUJYazMTpJgSYQZaZD5pve8kgckOskmIZBpPi++n3R62MrrCwtiYG+U9Ii+DI0eswFvJSp 8m0frx4I 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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: >>>>> If I am not wrong, that triggers: >>>>> >>>>> VM_WARN_ON_FOLIO(folio_test_large(folio) && >>>>>            !folio_test_large_rmappable(folio), folio); >>>>> >>>>> So we are trying to rmap a large folio that did not go through >>>>> folio_prep_large_rmappable(). > > Would someone mind explaining the rules to me for this? As far as I can see, > folio_prep_large_rmappable() just inits the _deferred_list and sets a flag so we > remember to deinit the list on destruction. Why can't we just init that list for > all folios order-2 or greater? Then everything is rmappable? I think we much rather want to look into moving all mapcount-related stuff into folio_prep_large_rmappable(). It doesn't make any sense to initialize that for any compound pages, especially the ones that will never get mapped to user space. > >>>>> >>>>> net/packet/af_packet.c calls vm_insert_page() on some pages/folios stoed >>>>> in the "struct packet_ring_buffer". No idea where that comes from, but I >>>>> suspect it's simply some compound allocation. >>>> Looks like: >>>>    alloc_pg_vec >>>>      alloc_one_pg_vec_page >>>>           gfp_t gfp_flags = GFP_KERNEL | __GFP_COMP | >>>>                             __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY; >>>> >>>>           buffer = (char *) __get_free_pages(gfp_flags, order); >>>> So you are right here... :). >>> >>> Hm, but I wonder if this something that's supposed to work or is this one of >>> the cases where we should actually use a VM_PFN mapping? >>> >>> It's not a pagecache(file/shmem) page after all. >>> >>> We could relax that check and document why we expect something that is not >>> marked rmappable. But it fells wrong. I suspect this should be a VM_PFNMAP >>> instead (like recent udmabuf changes). >> >> VM_PFNMAP looks correct. > > And why is making the folio rmappable and mapping it the normal way not the > right solution here? Because the folio could be order-1? Or something more profound? > Think about it: we are adding/removing a page from rmap handling that can *never* be looked up using the rmap because there is no rmap for these pages, and folio->index is just completely unexpressive. VM_MIXEDMAP doesn't have any linearity constraints. Logically, it doesn't make any sense to involve rmap code although it currently might work. validate_page_before_insert() blocks off most pages where the order-0 mapcount would be used for other purposes and everything would blow up. Looking at vm_insert_page(), this interface is only for pages the caller allocated. Maybe we should just not do any rmap accounting when mapping/unmapping these pages: not involve any rmap code, including mapcounts? vm_normal_page() works on these mappings, so we'd also have to skip rmap code when unmapping these pages etc. Maybe that's the whole reason we have the rmap handling here: to not special-case the unmap path. Alternatively, we can: (1) Require the caller to make sure large folios are rmappable. We already require allocations to be compound. Should be easy to add. (2) Allow non-rmappable folios in rmap code just for mapcount tracking. Confusing but possible. >> >> I do have another question: why do we just check the large folio >> rmappable? Does that mean order0 folio is always rmappable? >> We didn't really have a check for that I believe. We simply reject all pages in vm_insert_page() that are problematic because the pagecount is overloaded. >> I ask this because vm_insert_pages() is called in net/ipv4/tcp.c >> and drivers call vm_insert_page. I suppose they all need be VM_PFNMAP. Right, similar problem. -- Cheers, David / dhildenb