From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D0CC7606A31E for ; Tue, 27 Oct 2026 19:23:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=j3ud/ZuJ Received: by kanga.kvack.org (Postfix) id DA27A6B0737; Tue, 27 Oct 2026 15:23:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D7A266B073E; Tue, 27 Oct 2026 15:23:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C69C56B0742; Tue, 27 Oct 2026 15:23:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id A51C26B0737 for ; Tue, 27 Oct 2026 15:23:29 -0400 (EDT) Received: from smtpin20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 56CE4A8859 for ; Tue, 27 Oct 2026 19:23:29 +0000 (UTC) X-FDA: 85369380138.20.FC0039C Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf15.hostedemail.com (Postfix) with ESMTP id 94ABCA000D for ; Tue, 27 Oct 2026 19:23:27 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="j3ud/ZuJ"; spf=pass (imf15.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793129007; b=h8KDn1FTUxO4Po1Obbi7STNRfJIaDI0eyM3ueGYmAcWWKukIWkAPCu0WPIR+IsCBUaPG9O Ri00/NTQPYyE12HBN0NlcjTSQxCamPjpjjk2A4oPZxTXJqVdKgS9JsfaRuyNyXa0fyCdKF uV9Z3nsxjxCUFGADo6EIYBpT5AcMtfQ= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="j3ud/ZuJ"; spf=pass (imf15.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793129007; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=J9gSRb3D7ogtqu1SdrAnawsdd8oVJY1XtzaSrPDBAaU=; b=XSnWhd6t032FBqAcA3kY2WIt7a1nRVh3vGzpa2iGOIlHcNy7/JFwnxJwyDZJDSePNt+VcU sBjvXrhQzyN1eL06XKy1nySK/vzK1KCGrLdPYS4P58CZFuHjYfMjOSgQI8Rgg9CNLGITwf odE43faqAMdLfled/h31KP5ddV/u68w= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 3B474601F6; Tue, 27 Oct 2026 19:23:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1D6CD1F01825; Tue, 27 Oct 2026 19:23:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793129006; bh=J9gSRb3D7ogtqu1SdrAnawsdd8oVJY1XtzaSrPDBAaU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=j3ud/ZuJbVW9Ht6RBnRGEDrT32arwt0VIBU0qKDUNIniXzHqRWI+D+aEx8+VeUx89 HqHfaNjLOyNGKRWV6YgOkr68n3/qo9W0eMTZKINy2npz5GIar9UTvOFFdcSrtP0vv5 4jBkpsSuk2SY0/VYo17xyO/vRjQmaJgmQ0ymbf30GmQWIepsYBU+WJr0/di38WoRq+ kqm7EYhMmPqKzwKCAnGfYtn00aLBJbManBRnsv0Wg6USpxdVWqOa63F7st/2+ucXEw SHdY9czvzINbUIfc9qTtV8eJv4VO6GuzywLfFvmEu/vIFmsGBnaOmiDW2PK2xQnMZa 1n5n8XUqi4ceg== Message-ID: Date: Tue, 27 Oct 2026 20:21:33 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 23/46] mm/userfaultfd: write-lock the VMA before waking waiters when unregistering To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org, Josef Bacik References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-23-6f74bec9a5bb@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 94ABCA000D X-Stat-Signature: 84bry95s9shrf17eu4iu1m4qxf69xqkd X-Rspamd-Server: rspam01 X-Spam-Status: No, score=-7.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1793129007-794712 X-HE-Meta: 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 ziipu9e1 4Cln6PRZ2PNV18KPPor9GpahDuIv0OIb4FpIhgXP2lGFpYXyD+rf6FoTY9IJXlj281GpcMFRZrTPWrjDhpM+Iu03asZl2QVii6YOY7agbW2JYJMhUPD7ez7yEIXxWOUt1+/AUXkvoU7cQiD8N/xdUZA9ta9A1zI+i5xAK5C0LZRVGfNmYoMfr/zcSbu1SESwJSHMeRsQEv2D6OlOosaJ0MkXsKjO53B7lC2GTo+5nBlcAhigkmz1LtIpdMNqAJwNo1Ygt19/FPy77q1jjIrVRD1eeneYinyDyG9nmRr4gCErtoxabBeSbiT65Wphm1CeyO8iVc1dQzDuAXE0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/27/26 09:43, Lorenzo Stoakes (ARM) wrote: > On Tue, Oct 27, 2026 at 12:17:43AM +0100, David Hildenbrand (Arm) wrote: >> userfaultfd_unregister() wakes pending missing faults before clearing the >> VMA's userfaultfd registration. With per-VMA fault locking, holding >> mmap_lock for write does not prevent another fault from queuing after >> the wakeup but before userfaultfd_clear_vma() write-locks the VMA. That >> waiter can then remain asleep indefinitely. > > Oof. > > I guess userfaultfd_clear_vma() only implicitly takes the VMA write lock via > vma_modify_flags_uffd(). Yes. And the original AI fix wanted to reshuffle waiting because of that (stupid). -- Cheers, David