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 3567A606A31B for ; Tue, 27 Oct 2026 08:16:52 +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=DqgW1ogH Received: by kanga.kvack.org (Postfix) id 3D1AE6B0614; Tue, 27 Oct 2026 04:16:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3A9A86B0615; Tue, 27 Oct 2026 04:16:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2E7086B0616; Tue, 27 Oct 2026 04:16:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 0ED4F6B0614 for ; Tue, 27 Oct 2026 04:16:51 -0400 (EDT) Received: from smtpin13.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 93F911A066F for ; Tue, 27 Oct 2026 08:16:50 +0000 (UTC) X-FDA: 85367700180.13.D75D71C Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf05.hostedemail.com (Postfix) with ESMTP id D7A8C100006 for ; Tue, 27 Oct 2026 08:16:48 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=DqgW1ogH; spf=pass (imf05.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@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=1793089009; 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=25JoUd0Ca4DSucyqp8VdpaHvYyD4L6ugc8HcJwXmagI=; b=c29YGmo0G2DjMuVG2MIu6PthnVcJ5XZ0pUcFYn3ITQMUIwUIkOmvJSYJNykHMkEs/iap+g EGCQ4a6vpN5KSMFYNzUwBG2HegavC/OamiWDCQ70AhYoRhtwi1cAeQJlCDqFnFuKoA5obS 0S0DSAXu2YkSunGqARe5G7bXhjsErxw= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793089009; b=SqGzHkrDTV76wtkjIBPUjBrtHG50+Qn5x8yr9rEtOr49DWZ4KSRM7yG3OpYHr7JgV09zgV ouohLxBHOXySxJVVfYnfxBT4GjZkDaNtiZyplFcEw51mfJia/50y8Mx5ithRX4CZlOkToe UTRE855fNXHVKONAeHTTTEXL6S3q9Jw= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=DqgW1ogH; spf=pass (imf05.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 14E1740DBA; Tue, 27 Oct 2026 08:16:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB6EE1F01825; Tue, 27 Oct 2026 08:16:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793089008; bh=25JoUd0Ca4DSucyqp8VdpaHvYyD4L6ugc8HcJwXmagI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=DqgW1ogHskC3KjpnvkmfF/B2DYXhDZoPDNeziDRz5NYseOTPq/Bt3d/gR2uwOi5tt l0FKm0+vSEXyriWPhPAPthXH1Up+UF+85+8a4DRAWSbZRYMnvjqZUBuxtSS9VhexcH QjEToIVl39sflEhmYe9ziXX5NCu06RELjf5E7IRB4kHtHZXSvXfgKEoP26dOW1+9IE ffVmPh+WFa/36AqcOLOz1lEuekRW0rjPES5+SXPWLU9gfjD0+35/LrvlH8duWv+GbJ RuWAou4+YDgaZUIhlBwjRnVkYYWwTrj2jlqPucPxJ4gaehaWDjNNziTUjRRUgWOZSb cgzDt4LnM1kJg== Date: Tue, 27 Oct 2026 10:16:25 +0200 From: Mike Rapoport To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , 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-Server: rspam11 X-Rspamd-Queue-Id: D7A8C100006 X-Stat-Signature: ws4nu7o9xftjf64mpwy7spiw1z1pmn6c X-Rspam-User: 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-HE-Tag: 1793089008-284665 X-HE-Meta: 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 kB/M/DYE 4qiTr3xK56b//HL6PuebT92jWhbmMOimIJKgiXdZZibE4tofaKiBpYrB4JAMK3bUR6BEKis2TowM5JeghsuhPJIgo6HVDrOr+TkbRzGupg6ntYK65ZMSk3/rqIsvDvDPWk24o/npogsKcTCfZ+QwBmcfxP92UrEnF7w6jgAs0uH+fHee8F8rSYjjNgOka8kQ/H7I6pJfhHzJvNM7+YEj/7bcAFHOYiUrgJNzqTFUhsdh46ON8rMIRHt+ogW9G/LT1uyZXw1z0YN87MCH4tXvmKBKITrtUGMO9ednAsSlxyNbVg5vMGpYY4S34SBKZEXE60S7qU4qZbCPT2zRAql5o6fn4vnN31HWgPShkqoq+RhSBuntEGccHY/oznF0Q/FLHfIV1cMhn4g4F13X+bd2Xw6ha3QY5TfJw58Tm 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. > > 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(). > > 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: Mike Rapoport (Microsoft) > --- > 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 > -- Sincerely yours, Mike.