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=1793057106; b=kVC0Wtlp89km5Hbhe6NDRZjvfQMHgT9zgSmXx5wWuyM3xYbCKnSCt5m5LVupqlC3TKqv itcOFolX/JWUwnLkpVzOlP0tprN/SzGwpbtZS2lHAGRX/NvEUKXNfeyig3GZMO2a78CQZ Kk0VIhaDLdJ+0pn16q+7yiapttP1r1qAOeKUar8Eey2W3EvXG6EUsSYDBKtO7JulNNoDO ytSofv2UCbBks0CaKQ0aWzXlrGKhiHOmSKQhum705FT9NRvTiHpMGi8Cbr6W2qoJGsrK7 5MSiPitUPbcHCIx2UuDhU35BoN1IZigPEcW0PBq8oyRkAMUWUqc5IvNjCGfgvFzvLcA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793057106; 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=NWNJ/XENAKSS8XJu2StXXvDx4pA/ZlIpefLloruQ3+A=; b=XhnAiw+J4rPsXkeJR7Pe1jO2JTf2ZsO572FzVErFj0SAXoiHSpq/fAuDRYNeCN8/U5dD Q9sIifrN2kexXvr0veCAlvtSArWmXEeyiHLD/SFrZU22QWMfxD5x1zrCbwhTmm2IufwjM Clw5yPHBq4Rn6Om1Xmb9iCPsXxtl1Jx6eZTHRzYIs4nqgS+9FIZK3W8hF0ws+pEAqkHUK dE29r7Es3fX+jA5DBl5m+5JU5/EjkCbEi2GWRBfWdLM+ldrrod84PVt4RvGGPZEXrT7Qr yrqabkh4lQulswTRCxw7xKj2F4x95XJcFzElzuT4AJbJUEZtPST4+gq4g6TKVTC/+Ew== 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=XmfZUdKj; 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 E6CF7606A325; Mon, 26 Oct 2026 23:25:05 +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=XmfZUdKj Received: by smtp.kernel.org (Postfix) with ESMTPSA id BAC9B1F01825; Mon, 26 Oct 2026 23:24:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793057105; bh=NWNJ/XENAKSS8XJu2StXXvDx4pA/ZlIpefLloruQ3+A=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=XmfZUdKj2CDA3hO/9OSbirdo/tI8K3m4+KVIN68gYUkWYDqjcQkm5g1INwhB61XHz B7RwKeG1CHsN5S6OJkvQsHmA0cql1QWmgbZ5b07svv40y4SxyrPzL9VUHMao1+/lbv pDTINIXQaAyXCwuj/k/OuayFvhOlGgVfUtolZmXavmCRIrRKJuvsa8MOnJFaFRq87R SIHKlLe+V7Ng+b4lAvM+DKz0SlqtEc9SiBdUFWJwiu2lctCWh0cYkKTc28rEazIUI+ jxN1CCeJj3IYrRDtRR5yXE9lyp4+zAuIjWbwmIF85IHU5AghTyKrUsQAlewE4xpgIz p8s5ToS7ru13A== From: "David Hildenbrand (Arm)" Date: Tue, 27 Oct 2026 00:17:43 +0100 Subject: [PATCH 23/46] mm/userfaultfd: write-lock the VMA before waking waiters when unregistering X-Mailing-List: linux-kernel@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: <20261027-fixes_core-v1-23-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> In-Reply-To: <20261027-fixes_core-v1-0-6f74bec9a5bb@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=1288; i=david@kernel.org; h=from:subject:message-id; bh=SZZ0c1Ekk71/HNTctZ9IxQIrBH8id6NjD8hfDnFWvMg=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLLu35/m/ShOQ+gHDwePwf/j9sIbLn+O83as/W7OorTuo pR2iufujlIWBjEOBlkxRZag4PsGL1+uq61242OGmcPKBDKEgYtTACbyTpyR4dflzBz7RJm7Wi7e fkozPU4pZU8RvNeV+djcwsszqL8ghuF/+r1nL/aekqm5sah+zstDGa/fJO6drqF1452p++uS9GA 1fgA= 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 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 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