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b=glGQBqNc1KRIJY+4eXYuyo4x8xsdMn7qscU1jXE+LdfRxl8N3+y7ch4kG0XZEC13w Rst3Ki2cfX5RVngCHsPWS3TxlWdiwjCqWw+mxwEzj76Ld9oGrEEE8izN+Qlfp09h6k GQ6fflH7jVvzFIHnmKXBit/AboWC0MKEQ9gPQ1sRrS2y4uRLI8NqMbhvYFWTGM/Iih G8dYr0EG5rZhZ1lvCP0hlskJ7cRHzE+lxy37XUjT538hZGp+rif9cejL7L5Uvjxmmn Fw15ZFguBcITOg3hc+tfABh/s03IszofdxDKfTadhI+XvKL1DGOGrxGHDxhg1QUZVw Sb6pbD0NFEMfg== Message-ID: Date: Mon, 11 May 2026 14:18:13 +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 Cc: Andrew Morton , 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> <3a04ae6a-049f-4d3d-b5c9-e60e86be8e5a@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: b7b1h1rbsfru3zm3xe44g4c11kqzen8g X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 0BB3D40012 X-Rspam-User: X-HE-Tag: 1778501897-634272 X-HE-Meta: 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 KBJYcT57 W5sTEMJm6mEGz5REaxb41L3fv0LZxefqhD7MvoXjq5dsfxf366wa1R4QemrJ5ZJTCY0Vtpcip2+m6HPs7+YgHtU0zJuUdwzt9TWt1oG37tHUv1YYfJ4b+h3qKl0U3vdgWIq5lBu0zNIAL7rbwGzh7KPVq45msoTtUtoTisln7aMPKDVp0NfzLuEsVSXmQtQbGSIV+cGRYYE7SbxuuudYIMz2gAuAUcO+vpO1bjeeca52toGUbkuy6IUnVJ8g781NUtva3kjYccMg6qNf9OndQp/FzJ0EA6gVZ4YwsDOWrpFA3H49j924r9Eniqa2Tz5bAfueLUNvQ/P5pD/j6FqK/rlG10wXfYFFTjBt9IWu75nUWmhsbBPIWS5I8ca0YWdqzeyuc Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/11/26 12:48, Mike Rapoport wrote: > On Mon, May 11, 2026 at 11:15:34AM +0200, David Hildenbrand (Arm) wrote: >> 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? > > Yes. > >>> 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? > > Yeah, we could. In any case Reviewed-by: David Hildenbrand (Arm) -- Cheers, David