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[2003:d8:2f22:1000:d72d:fd5f:4118:c70b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-437c74c65b7sm202921535e9.23.2025.01.20.06.02.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jan 2025 06:02:07 -0800 (PST) Message-ID: <996a7582-a0a4-4fe2-a156-0112c7f12ade@redhat.com> Date: Mon, 20 Jan 2025 15:02:04 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: khugepaged: fix call hpage_collapse_scan_file() for anonymous vma To: Yang Shi , Liu Shixin , Andrew Morton , Chengming Zhou , Matthew Wilcox , Kefeng Wang , Nanyong Sun , Muchun Song , Qi Zheng , Johannes Weiner Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250111034511.2223353-1-liushixin2@huawei.com> <8a561ea1-56d5-4914-8186-f0546a84dcb2@os.amperecomputing.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: <8a561ea1-56d5-4914-8186-f0546a84dcb2@os.amperecomputing.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: oaiShA2jNBOmnVVA_0WEbQMO0BNuuj4zyv6pqSIUF00_1737381732 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 63653C000F X-Stat-Signature: s3k8duupciwg9dcyotdrpjbhnd4pwra6 X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1737381735-550598 X-HE-Meta: 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 z1TgmUvK 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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 14.01.25 19:00, Yang Shi wrote: > > > > On 1/14/25 8:56 AM, David Hildenbrand wrote: >> On 11.01.25 04:45, Liu Shixin wrote: >>> syzkaller reported such a BUG_ON(): >>> >>>   ------------[ cut here ]------------ >>>   kernel BUG at mm/khugepaged.c:1835! >>>   Internal error: Oops - BUG: 00000000f2000800 [#1] SMP >>>   ... >>>   CPU: 6 UID: 0 PID: 8009 Comm: syz.15.106 Kdump: loaded Tainted: >>> G        W          6.13.0-rc6 #22 >>>   Tainted: [W]=WARN >>>   Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 >>>   pstate: 00400005 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) >>>   pc : collapse_file+0xa44/0x1400 >>>   lr : collapse_file+0x88/0x1400 >>>   sp : ffff80008afe3a60 >>>   ... >>>   Call trace: >>>    collapse_file+0xa44/0x1400 (P) >>>    hpage_collapse_scan_file+0x278/0x400 >>>    madvise_collapse+0x1bc/0x678 >>>    madvise_vma_behavior+0x32c/0x448 >>>    madvise_walk_vmas.constprop.0+0xbc/0x140 >>>    do_madvise.part.0+0xdc/0x2c8 >>>    __arm64_sys_madvise+0x68/0x88 >>>    invoke_syscall+0x50/0x120 >>>    el0_svc_common.constprop.0+0xc8/0xf0 >>>    do_el0_svc+0x24/0x38 >>>    el0_svc+0x34/0x128 >>>    el0t_64_sync_handler+0xc8/0xd0 >>>    el0t_64_sync+0x190/0x198 >>> >>> This indicates that the pgoff is unaligned. After analysis, I confirm >>> the vma is mapped to /dev/zero. Such a vma certainly has vm_file, but >>> it is set to anonymous by mmap_zero(). So even if it's mmapped by >>> 2m-unaligned, it can pass the check in thp_vma_allowable_order() as it >>> is an anonymous-mmap, but then be collapsed as a file-mmap. >>> >>> It seems the problem has existed for a long time, but actually, since >>> we have khugepaged_max_ptes_none check before, we will skip collapse it >>> as it is /dev/zero and so has no present page. But commit d8ea7cc8547c >>> limit the check for only khugepaged, so the BUG_ON() can be triggered >>> by madvise_collapse(). >>> >>> Add vma_is_anonymous() check to make such vma be processed by >>> hpage_collapse_scan_pmd(). >>> >>> Fixes: d8ea7cc8547c ("mm/khugepaged: add flag to predicate >>> khugepaged-only behavior") >>> Signed-off-by: Liu Shixin >>> --- >>> v1->v2: Remove the redundant vm_file check, suggested by Matthew Wilcox. >>> >>>   mm/khugepaged.c | 4 ++-- >>>   1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>> index 653dbb1ff05c..bad1e130eda8 100644 >>> --- a/mm/khugepaged.c >>> +++ b/mm/khugepaged.c >>> @@ -2422,7 +2422,7 @@ static unsigned int >>> khugepaged_scan_mm_slot(unsigned int pages, int *result, >>>               VM_BUG_ON(khugepaged_scan.address < hstart || >>>                     khugepaged_scan.address + HPAGE_PMD_SIZE > >>>                     hend); >>> -            if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) { >>> +            if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) { >>>                   struct file *file = get_file(vma->vm_file); >>>                   pgoff_t pgoff = linear_page_index(vma, >>>                           khugepaged_scan.address); >>> @@ -2768,7 +2768,7 @@ int madvise_collapse(struct vm_area_struct >>> *vma, struct vm_area_struct **prev, >>>           mmap_assert_locked(mm); >>>           memset(cc->node_load, 0, sizeof(cc->node_load)); >>>           nodes_clear(cc->alloc_nmask); >>> -        if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) { >>> +        if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) { >>>               struct file *file = get_file(vma->vm_file); >>>               pgoff_t pgoff = linear_page_index(vma, addr); >> >> Acked-by: David Hildenbrand >> >> The whole CONFIG_SHMEM is all weird and needs to be cleaned up ... at >> some point. >> >> BTW, do we correctly handle MAP_PRIVATE of these files, where we would >> have vma->vm_file and !vma_is_anonymous(vma), but could end up having >> anonymous pages in there? > > > I think so. There are a couple of cases if I don't miss something: > > 1. non-shmem: khugepaged just supports collapse read-only opened regular > file at this point, there should be no anonymous pages in this case > 2. Shmem: >     2.1. small folios in page cache: it should be fine to collapse page > cache itself even though there are anonymous pages >     2.2. large folios in page cache: khugepaged should bail out from > collapse_pte_mapped_thp() if CoW'ed anonymous folio is met > Great, thanks! -- Cheers, David / dhildenb