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=1794273212; b=3VTC4TJdGWItPf4hUPX0KR+uo0CsMNuijhonkDCKhPNEDeABA0kUM+lDlRdzU8wDmkXR HcJLoxZGOp2z4X5v5EmRpvJu0QioXNpYFjFTmv4ZwaFUwXgns/ZWXlU4nuyPJyyP+q9wn jjUDHdlEkLZEckH2xptMU10j91ZvjJjKVD70fOaFHyISQCXW5y4Qr+h1G9yvso53BipHu BgrSAEKuTNy9/EscVtEvJ5DJxvx6wUjWOLOVGCPrh6tLTwlD2ORlFLiRSpNwN8mh6ho7m Lj218/LKaoHzEm0FDhG5xk0KMZ0/BiWZKfSh9/X5yncOE4GFBHrQMd9yR9zIssdL2YQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794273212; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=9nU557c0kDDCXR1md+W2gXlS+vjp4yxM4KBf2jRbexk=; b=dT2y1JSnX+YFQ9bdfPd3wro37xW+PS3m4ZwJGfZYlsH79Qj0PSUn6tWF+tN99B/nSPYS QX4345V1vL9fr/3x3VfHQBuQZDDBD27QxUlPM8yxmIDo9d0XJ2T8x9RnQM9efDsayFJ8I wujhih2Kod/Mx2Sx1Q5EJRiqFq3fEmRLuIrm8SSUEEbel4ZhwUaBxLg/c6nX4c08j+aZc o0xSw3kVTfeFmeukBEtWcQ43rKpZhIFu14oSFFcrWfeF4uCVHxHcvT0k3MV2Iy6ow2Fv2 p665B3WJ2ETzDkBc237SZPgDEeBuDBdm0MErbEdF4M58PlA9Qg+EOv/z6IxZtJEZOMg== 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=cgGWXoaS; 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 C5AC4606A31C for ; Tue, 10 Nov 2026 01:13:31 +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=cgGWXoaS Received: by smtp.kernel.org (Postfix) with ESMTPSA id 86ED71F0089F; Tue, 10 Nov 2026 01:13:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794273211; bh=9nU557c0kDDCXR1md+W2gXlS+vjp4yxM4KBf2jRbexk=; h=From:To:Cc:Subject:Date; b=cgGWXoaSiZTED8vOzN+fhuJiEmWRsH/uM5nSG7p1Jd/KxELVqPBNLFXvPJae5CsYF Q1HIGaXuHaVJ9Wuq8m7zddORSuJFvyd8l425zyrMRapPGSYDzUe+A3yEJF8oOPS1Qm WBmrbrmY9Hc3dQjRFfNhFRlz9Abj93R2bxBV9mS9dxHx2y3LZzR+hBtMQjdr/GAhwH vCY5CN6hKwss7ieneQKeNaAT2jAvljzYRD23iHOTa2ZQgj4VoP9qCs8uSrmoW5CysW aMZACdmVTSPa1jGUZjNmX1foKv9PanGdtDM0Zu3plis1Pm6f425xa7gmXVwQmsTGeA p4WkPJN4BXlSw== 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 6.6-stable tree Date: Mon, 9 Nov 2026 20:13:29 -0500 Message-ID: <20261109201329-failed-6.6-35f7ecd55ce7@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 6.6-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-6.6.y git checkout FETCH_HEAD git cherry-pick -x 35f7ecd55ce7e51cb6d5ef49e6dd51f3c80f61e4 # git commit -s git send-email --to '' --in-reply-to '20261109201329-failed-6.6-35f7ecd55ce7@kernel.org' --subject-prefix 'PATCH 6.6.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