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=1794272948; b=Rhsi8XdPhpe0sFsKfpKZ/gDW/bjbBO71CkWunexGMQeZqW/REf1JX/h+0/Nh2zhA5sUh Nxv4Vy1IpH5GiWgwly6SBZbAe+8y+GrZeoLMLyQHvcQJxX+yZAySWD4ToHG+oga86/fBd H8xsaUdUBUhoyXzoTM2/14LjnclquROqtv0GBiR5qcwYrR3ll3oe5yjT+vJxaDjFWCFWj Xw/W8bc1B4C4dOUIAvsoJ1JpvsS/VLPfiukhlo+mlZuvzUreCiApLYLoHgSJn8SyIwzYC 9QDjHZv6HQKs3RrC2t17q8Md2Ia4JrXrOSyeoU+Nn2AmfQ9tE9Pu4ROIrW4b8zBtMRA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794272948; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=1ZgP++7U1D5uNGrNu7HGK8sr20q9QV+NwvivNmfU2cE=; b=R4OFjZWnM920w22utEtGMk3oqESTLllJLPUvBRQnqwR2ax3fSK3xueBjdUUh/MuhIQO2 SK2NZrKVTc+MzugtTX5IvO1ItjJHoUBnpcHfiuIfrwmkhuh52fVIQeKH6f27/6v5/1GLL 3JhQ7qcx4em+kQjJbkswUlKUVNZuj1FKtqkd1tlplG8ao1SMbA53cB12ugLCQ9sg7GliZ keb9aomGukltaHzUpEG7IZjP6aSglRJ9/lGsy0dNBAcoIgDhCHvkvI4/HrU2zhgJm6R1L rviaTyj0y/wWJ0arvEfZVHBfcKu5MxDSe6dV3sO8aR94Qv363kbaLQ8wsdDMckKQtYw== 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=JW08M55d; 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 D1156606A31C for ; Tue, 10 Nov 2026 01:09:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=JW08M55d Received: by smtp.kernel.org (Postfix) with ESMTPSA id E06971F0089F; Tue, 10 Nov 2026 01:09:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794272947; bh=1ZgP++7U1D5uNGrNu7HGK8sr20q9QV+NwvivNmfU2cE=; h=From:To:Cc:Subject:Date; b=JW08M55dDxlpeQHg7OkWL5G617GbyvAPR/qY5zUK8l8lLqKkXy1ko0BrDlpm4SoQI No6Y79dge9BgzTJtlJqVGOce2zWi7JRXRKAOqvIRrkK/iuIiFAmGFvpzQetsVyjX/J r2UUZHOm11n9iSLzDjZ2dvzgjoJDc0tkIX2GA/sXLZbb65fl6C+FRVJ3h5xWYtkvrq JHK1t1qtNBx8UFxqITwm7oN9fGmWMCuVdbopGSaDaS7I/D3kbNpOJARXqzjarLAP2v mO3RdBuMHR/CtDBIEQXj23nEarjX8J81IzOtR/4pYht3hxkssDQmm9+0VkZa4wo200 sgW0e4DRw7p2g== From: Sasha Levin To: david@kernel.org, josef@toxicpanda.com, rppt@kernel.org, ljs@kernel.org, surenb@google.com, usama.anjum@arm.com Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] mm/userfaultfd: write-lock the VMA before waking waiters when unregistering" failed to apply to 6.12-stable tree Date: Mon, 9 Nov 2026 20:09:05 -0500 Message-ID: <20261109200905-failed-6.12-35f7ecd55ce7@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@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: 8bit The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 35f7ecd55ce7e51cb6d5ef49e6dd51f3c80f61e4 # git commit -s git send-email --to '' --in-reply-to '20261109200905-failed-6.12-35f7ecd55ce7@kernel.org' --subject-prefix 'PATCH 6.12.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 35f7ecd55ce7e51cb6d5ef49e6dd51f3c80f61e4 Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Sat, 31 Oct 2026 10:39:52 +0100 Subject: [PATCH] mm/userfaultfd: write-lock the VMA before waking waiters when unregistering 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 Link: https://patch.msgid.link/20261031-fixes_core-v3-23-d6437171ecc3@kernel.org 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 -- 2.53.0