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b=YXv1Nkm3xbY6GJx8oQhu2MsMgulMHa/cQoMnyJw1P1KEgOk/H/al3/FHoNEDlhm3C dizgRDOwzPBdRREetZv+k2tzchrbJ5e06Gh26ci4WJZFzvtWYKhtXddU9Slgu/xmon X+mM1Y0hEdfrQjqkw8x9jvIRY1ASBq5lAWyxE0PCPHZqDqGSlVOwtGkFFJDK4W9MY+ ok4YO2iZIzBJqOtbfpEFr922lA4R9OlgMjkS9WvYERbGzP8FTBKcomH6anAsll7FY2 qXBtdy4Bhj9iXZ+j5kfgj8iqKfNTABUgAJNChvmy66GGpEudTfKBxwVE7xoQ/9+oIl /hQNGn7OAISxA== Message-ID: <3a04ae6a-049f-4d3d-b5c9-e60e86be8e5a@kernel.org> Date: Mon, 11 May 2026 11:15:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] userfaultfd: ensure mremap_userfaultfd_fail() releases mmap_changing To: Mike Rapoport , Andrew Morton Cc: Alexander Viro , Christian Brauner , Jan Kara , Peter Xu , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260501145433.156211-1-rppt@kernel.org> <20260501145433.156211-2-rppt@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <20260501145433.156211-2-rppt@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 36DDDC0007 X-Rspam-User: X-Stat-Signature: mr7gb1z58w35ku9tse4nmip8ky8ouoor X-HE-Tag: 1778490938-49350 X-HE-Meta: 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 dL1Xrwi5 ZpIt2AJT+LkmiVRRf3eQaQ9oRrspXZQQNVp8c7efkjsS9PMMzB8wBoSB8TtEb2rZO2wbs2SmWnPm9b9EqsLBEufOXSUqtyqxgOYTMIcSYj0if2oetG267gfG9GB/RS3rx6biPcKWCRozzad4Tk0cDLvo1Q2U+quc6BzYz3DihYVo9sgog6VbCW/bS9cj5A1LHKR9g6i9KTYC/tpMsGxif98Lv9lx66h87ZX+eOli/3qh4sTQRTR3PpIdqiXbYw5ThsW0jOWyQYY798U8rAsVhwDZtCW+Ne9QRiOFlv2IdQsghPzg0OQoD5j0JiF0mtzxFnSylSTfWg2OlFoeRlogGAnBXtN2bqXNZEpUJ/kfQ5gjatDqK6BYq6UzsKu0XUZDAtZBb Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/1/26 16:54, Mike Rapoport wrote: > From: "Mike Rapoport (Microsoft)" > > Sashiko says: > > mremap_userfaultfd_prep() increments ctx->mmap_changing to stall > concurrent operations, but mremap_userfaultfd_fail() does not > decrement it before dropping the context reference. > > If an mremap operation fails, ctx->mmap_changing remains elevated. This > will causes subsequent userfaultfd operations like a UFFDIO_COPY to fail > with -EAGAIN. > Sounds like we should CC stable? > Decrement ctx->mmap_changing in mremap_userfaultfd_fail(). > > Link: https://sashiko.dev/#/patchset/20260430113512.115938-1-rppt@kernel.org > Fixes: df2cc96e7701 ("userfaultfd: prevent non-cooperative events vs mcopy_atomic races") > Signed-off-by: Mike Rapoport (Microsoft) > --- > fs/userfaultfd.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index 4b53dc4a3266..ef963a58f1a1 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -786,6 +786,7 @@ void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *vm_ctx) > if (!ctx) > return; > > + atomic_dec(&ctx->mmap_changing); I'll note that other users have a VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0); In there. Likely we should do the same? -- Cheers, David