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=1793439974; b=ufFhD3tTGIidNsejAfPdLvNaZELteVafx4TYLPuF6P8EWGrEGVAWn29Rk9EfJgG9HBPi Pn3p14/IwgJpPv/f9j5S1JjYecwrdGa6Zt693x4AyvPM5Zr9dqfQ5q2DlxRmk4CITS9NW 7NLVvt2Qn0SgNy6k57eLs6diWgok0NI2ppCpC9bXRS1lOWoP88zV8ctQoKiaDddOnlCD+ PJejQYAaR23xy6PsrIIJv9c/YYXUx1TngjupUvQNcTQbhGcKv6kd8mVdBlbIj3qKwRIDI AK00QhDWB42M0T3LRz3R1NYaTBEtfRGyz4ktGwvvzhsMeNcl8vG3cCL95Imu9W3LP1w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793439974; 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=4sgsef0PgIF0cfrADdJuNAAJq268avrj1EIWVyDlN9A=; b=AzN3tPvw/Y19J/eGQq7YPFjRKC7NSLuC8qzaSJZdkHl2HXwhnMb1BFEIIrpMmeJHIkD/ 73xztfNsdy/Fq8SAplMjBWrFvRgYcxe4ldvDJNpNL/8+JprtPrshwZiO1YGkAfzLP2llN XZGp8fjLriV+2B4YU5dydVWvVQhEqcmx+te116ZWw7k/zo34o6xuc67Uor0o+0mD5Hbgr 5BUhS00y88iHaj4AohDxEf+c6819LkbTi98BLYW74gbp7KSAnPt9jKtE96icrU4AQlHjS EzziJVRGbzTfQB2La5bzYKmCJQQAyYbDx4wCKJBOs2Em6e0oUWjEip0KLsYusnYJBLA== 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=d6CFfneP; 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)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 48082606A321; Sat, 31 Oct 2026 09:46:13 +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=d6CFfneP Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6136E1F000C1; Sat, 31 Oct 2026 09:45:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793439973; bh=4sgsef0PgIF0cfrADdJuNAAJq268avrj1EIWVyDlN9A=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=d6CFfnePukIWxq1RflVVt4wxWBc+6vCaK03YtXkPiVGAT1MLhmGttqbCKpZC8CMv0 ykZG9YuZhqJBGj8aR09OSLgRuWTYMZWKwLUnOtAFD0NmRWhh/hkNYdyjvdkGrtM/HC NvXMCLg235yYjJ1P9mJHTNNH7LQX4WGY6VQxjXRLERdE7L37vvhfQideQle/aO4CF2 rz9IJxRxQ+TD0DOdP47cmawMrJuPX8KczA2npuhKSEktnAwI/DZutaxbl1koK56PVe 4Qx6oqX4wL1+I/FemH+A6y6sdwfYTdtWxi7NEEoGuMBtRUXETKv8bzi+XlHEkQntS7 4jzXemYA3bcMA== From: "David Hildenbrand (Arm)" Date: Sat, 31 Oct 2026 10:39:52 +0100 Subject: [PATCH v3 23/47] mm/userfaultfd: write-lock the VMA before waking waiters when unregistering X-Mailing-List: linux-cxl@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: <20261031-fixes_core-v3-23-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-0-d6437171ecc3@kernel.org> In-Reply-To: <20261031-fixes_core-v3-0-d6437171ecc3@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 , Muhammad Usama Anjum , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1507; i=david@kernel.org; h=from:subject:message-id; bh=wm0iwUtDDosDLjqj9xBcxV65LFmKykeK8WHMHyZPLHw=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLKebs+QOvwkeiXTRJbcv69PJk23spi0JO3lV54Jugxc1 +3fPj4R2VHKwiDGwSArpsgSFHzf4OXLdbXVbnzMMHNYmUCGMHBxCsBEXhkw/K8Jnfd9x5bTzUxX pftZNxgezJ8YN90hhLtU3enYreUr/mQwMlwUz5Tcc+IGq0Txmea3//4c6PzmP2uueYjKLiaP75X zrrMAAA== 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 Tested-by: Muhammad Usama Anjum 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 928ad95eeb2ba..3ca04b582329f 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