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 27318606A31E for ; Tue, 27 Oct 2026 08:43:36 +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=WzfqTN9d Received: by kanga.kvack.org (Postfix) id 25C5D6B0628; Tue, 27 Oct 2026 04:43:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 20AE06B0629; Tue, 27 Oct 2026 04:43:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0D4FE6B062A; Tue, 27 Oct 2026 04:43:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id D22C06B0628 for ; Tue, 27 Oct 2026 04:43:34 -0400 (EDT) Received: from smtpin14.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 4C17EA09A5 for ; Tue, 27 Oct 2026 08:43:34 +0000 (UTC) X-FDA: 85367767548.14.B5DC839 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf09.hostedemail.com (Postfix) with ESMTP id AAF48140005 for ; Tue, 27 Oct 2026 08:43:32 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=WzfqTN9d; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf09.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793090612; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=dHr232roZz4zxvNcr7fz7EZ96bBQfhBelI7N1e6dtIg=; b=ibt+Z2yiLcTgB4k75c2iMA3R+mGc3scAv1zy1eNIzIkw3nLiZGgt/1TuEy/S7vBdmpjux1 U2JaCSsdSpKrQ4Yh30BFH+G5lJWqouAyU/27B/E+I77OMerZcUWzLz4ZR6WDnGHoGYgPkP K6PMdJG51dLoO1toguqIMdh5zJ3NZmI= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=WzfqTN9d; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf09.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793090612; b=wBlz3+PbTHKAU/VNBj1iTsXFLnsyJAWpyiZlkTWcZLVhb8BI7NSGTkjJWfQBKIGn+V8qqL V7aHL5yREDyighCTBGJ1oUaO5ilVo+XDwc68MgfJOWhPW5NJAJfBmC3MsABI8cmGFDUpY0 eTGYhlwmiB0FBpiF73jCCJ9q5cswolQ= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 36E81601FE; Tue, 27 Oct 2026 08:43:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9500B1F01829; Tue, 27 Oct 2026 08:43:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793090611; bh=dHr232roZz4zxvNcr7fz7EZ96bBQfhBelI7N1e6dtIg=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=WzfqTN9dybqeLWoA8oUAZ1tXSG8xyenSoildQDFUPskrIwuh0Om8GmkGOBhQ5FsqX 3B6I40g9wmGk8NCIIhxhAbDqi/ZMQNeLz88bXgkLZL9wp3hp24AVldencxxNOmO56E 4Dk/LyzP9i6+CjPNOmovIvMvgBMfOCP5ftzi7ttPrA1HXuEw+YPYQEt8JuPCPhU9Qh FTU2I/BXKFE66SYqvBcFQdHZeCq08jT60hhxAZK8vNRyQ92PVr8LzDAXu2OR6KFYh4 ggHTOX/ZZnJQfYnUIldz4DBR8skhm8PsS7DC9s4XnGtCHDusD1BrLy77dRYwXUQQzN YEpV0CA1ETDaQ== Date: Tue, 27 Oct 2026 08:43:14 +0000 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (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 Subject: Re: [PATCH 23/46] mm/userfaultfd: write-lock the VMA before waking waiters when unregistering Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-23-6f74bec9a5bb@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261027-fixes_core-v1-23-6f74bec9a5bb@kernel.org> X-Rspamd-Queue-Id: AAF48140005 X-Stat-Signature: 1dtn4co5zm7kjnxt8g6ppo9ipm4m1w1s X-Spam-Status: No, score=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1793090612-380959 X-HE-Meta: U2FsdGVkX18JpDmwAjujCFMQz7YNVBt/OcXwf8EZnVKEDLvXSUBCGhaCiXTGjXProFZLUZdno78JBu8B5Wc7iYS53rxcS0QFkaq1Cu6/WC63hb6RjahaogpXuwbGWcFh4vGpbmWwb7vCRP3HLZiXWQ413UDey5VOc5pjqiWsR8TF4DduddHOVMC1KUBGaeA5BKHySwrC2Y/z28fV8KYlQfp04Uxoj+DBoq3KqCVNj/DHoWQ92Q+UMCGRX3gLWr0cc4aMQcnTcKQw3h5i42lojKkHMIKB+pkXZSrXsw5XYrDcMqxR/fzUF7uHDSZZnXt6+enS74O2Rl2FzXVEmRWYIgwscWJNrW3GxSz25E6ujE7cPdLmOPvIDQjxgd/ZV+ixqv4//wXE+7FvM1Rux3Ma+Nj64JttVgIqyNvyZ9Mi697hJ6CJo0xyQKuknrCD7OsGnae6+RuUv85MEJSBe5AchcHc7NuByUmIDMUiHQbTK+Fb+/K5aTVweEVhB7MtThPhFdsdPFuXzf+d/dIE3CdcbXrt4eD118kDVtXmhjOj8z/J2lsrswj20lwbzJMhiT3qHuPxfCN7v+/bzJrob84lh0gALvUn+Q9J10i+GXuN7XilhSuvaq6hqZogkwm+2SFBBGl6GpAdXJ+dieTHpkuwWj5E8uWbAkkeE8MYIjl/Wc3cqnbmiyQVOXm2hnZkVdyhp4PplPpyceNXoYjcJnhM7nQbtQaMMZbHwl5mT8I+JDbjCEZkBsV6cbQaWDDvIo4EsfjWhwqq2pItkrB0JW0C+lpdklGKno6R0pEKDeoyipi/JkvC+6LdjLjNg61D1xS+IBnKbT0kwvd03L/zr9+aEmBMtYOHhevZ9FiN8CeUCm1NMzCNN9C/rqPcIU3E9tZ75Mx+eSO2e2fvirj9bLRlA7sUhDRrn2SzU1lQiRA+/Z0Hkh/sNnsg+xNt9WIZGP+RHdovXyD7486KNGkA391 Jm9WQAxJ IFvaS94tA62PmjZH/XW0y7nSXVbsRM+ahGEl4OnMXy8jk2AD9E4StRHubGoZoMQqGTgT+QX90ouMIbZnfKKM+kqeoL/XQCfFbQQMPuBY2F56ICazyYim9/xEQZ5gGuBtNaw0m5Ih/peZN8FJn6CTckEKvX5HoTkhTfWC+UqjXFEDIqnTXHehBXux+Qt9KBRQSiLRyASLnnJaXto2HQ4j5aaB44m45eSWMiH8qQRBeftBg8e9v9/TCZteIGEx/3rmfpsASrDr/URwRJxcphbajmGG2hj458vNMCKjEhE5WDRs4OTsBht8h1TOZji694Xmh1JJFoCyfwXwq/8Hd/fzw8BaH0eglg+KH2knjDcJ8IXwN1SDkNsGRBMg5YZfkKIjtOV+PSb5lbGZ8OUZ2bINOjmu/9Xg+PAwT5XC0 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 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(). > > Call vma_start_write() before waking waiters. Existing fault handlers > queue themselves before dropping the VMA read lock, and new readers are > excluded until mmap_write_unlock(). Clearly an oversight from the VMA locks work. I guess was always a Herculean task to catch every single point at which there is an implicit assumption that mmap write lock ~ readers (esp. faults) excluded. > > Fixes: 29a22b9e08d7 ("mm: handle userfaults under VMA lock") > Cc: stable@vger.kernel.org > Reported-by: Josef Bacik > Signed-off-by: David Hildenbrand (Arm) Reviewed-by: Lorenzo Stoakes (ARM) > --- > mm/userfaultfd.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 669f71d485d02..7e30b5ff17be1 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -3991,6 +3991,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, > start = vma->vm_start; > vma_end = min(end, vma->vm_end); > > + /* Prevent new userfaults from being queued after the wakeup. */ > + vma_start_write(vma); > + > if (userfaultfd_missing(vma)) { > /* > * Wake any concurrent pending userfault while > > -- > 2.43.0 > -- Cheers, Lorenzo