From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793306349; b=pt2o0sNJ9zSYt5Bq9TuR8xaMriIphoLqoJ5VW4PE9iMomTIqF/tPt3JX5ywIgiIKStNQ LyzAYEsJkRRTU2BTNjZCdp+zSK/15ogwLtzlJd+Abh8nCthScdvXi+tlbDdyEsuPpQuZx pq349Qx7Q1NBEQel1ghOmR4RswiHp7frHY15EmoUpAdgMXK6qqVUpZSF1r0zELCVlVYtB pJIr7NJPGyCfRB5m24sIX9eViC/GwJN/839rcLke8HaegAfekGcJC6EKMk0YnsMFZQ+ZF j6MSRvOiGhgtw+/auenNkfTBFP73NM8bhgLTh23uGdcuBih+/hn6AarlP6OUbUxCiGA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793306349; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=zVfPl9MgmcK9sfU4MC+6S2mU4/7MWZEGtGJA+Gf+TwM=; b=ALenkbTZgxt4975Mcnh+YLWU28reYVCYlNA+MBfUWsJUaA20RnqBUk+L+h5M41xzsT1e D3HZVClVSKSr45n6yXxP69PyR5RClDy4WoW3yT5G31wJr7LjERIMrW9skgBa5nA/6aCOW YHEi6qVG3pbM5Jek8PsY5b+/UbB/cZgOXY+j85hOar2IPPZZaQ6aa3Zx9EO1T4ag5MKwL LIdEQDfD1RW95N5hOi2qfSp+g0VFCFSomOLTZdGeg28N7BT3dGe47UjLQLeKNkZSj2k8H IFZOWJR8Le3exKpSPZrj66l6w7L0yJy8pBmzBjRLvhvwGVgVlAzpg1wA1+LzTk/Enmg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=kz2AvSL8; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 79132606A31F; Thu, 29 Oct 2026 20:39:09 +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=kz2AvSL8 Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA2931F01816; Thu, 29 Oct 2026 20:38:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793306349; bh=zVfPl9MgmcK9sfU4MC+6S2mU4/7MWZEGtGJA+Gf+TwM=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=kz2AvSL81IHV86Y6xy2E2U1XsKVedZLudNnrvAi3R6LwSOiwulMVFEkdVCzj4b8mv cJ/ZZkh2/Qx6UTpNE9wJoAwwaFh0wJfMLmQ0UiYfsRcVlWXuz1oEdtl2LTA6ma+W5x 3G1d5jMl2VufXF/QWz5sAP0Jlxt6/O4yznwAno24YQ7K4D9RBffWJ2vgS8qltPFrTW 3YgpmX34se9pgvw5ePx/p+4vJRq/wFoerwCOuFB1DR0jPYIlQXh2pB8yM2wDRftfk3 hBeJr9FkYgsni8V/+/N91Qkn21XvQjId4eyK8MYKS0mxlR97xpOYo7FctBaQluZQ+I ZdiJ2oJGbuUng== From: "David Hildenbrand (Arm)" Date: Thu, 29 Oct 2026 21:33:18 +0100 Subject: [PATCH v2 23/47] mm/userfaultfd: write-lock the VMA before waking waiters when unregistering X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261029-fixes_core-v2-23-a64ce7f83abb@kernel.org> References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> In-Reply-To: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> To: 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 , 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 Cc: 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 , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1450; i=david@kernel.org; h=from:subject:message-id; bh=sxKVqTRFf7nv8Rk2AxGSEpTSCRWGcpA8V6JR+zulqqE=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIer21/Yxakd+CiyJNQ2zmOll9uxhntdKtc5rXnK8v9R bvilHO3dpSyMIhxMMiKKbIEBd83ePlyXW21Gx8zzBxWJpAhDFycAjCRU5MZGZpnb8kptntYn2z6 juHxPK+NosJMz3KrSvRVGLyezRR/d5mR4eqGdRYB9WncadsXKvz9e8UqQCpxh9x/Pre6y5vCz0x 2ZQAA X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A 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 Reviewed-by: Mike Rapoport (Microsoft) Reviewed-by: Lorenzo Stoakes (ARM) Reviewed-by: Suren Baghdasaryan Signed-off-by: David Hildenbrand (Arm) --- mm/userfaultfd.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 928ad95eeb2b..3ca04b582329 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