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=1793057350; b=Vgh8bFdy1DH+ZX480hdvevReYQKC570rguiAgmzS/mqkmIslvrQTasNq4B4INR9Sj7QS 2EgE8d7Mix+X3DXQrfY6bbXF/h6vByVGe334doWSE6GyK2/JtDJTXO94d14HAGGI1k92z q076qNDj73Y91iVqirzVCCGkxz/B64Twpu90U8O8PQMAoqpmZYOF9BxRQB4Ir4cHuuOfP TehLgNebIv0RqbtN0q9WzUOvb1VIaTGsnieDOdJpXamxrMUohCKjHrxtMnKbxDRjpPmmc 1fPmE27hnbGVxHsdodxxYA+VCJUq9C4ldrOuEyCKu61TbXHrCOZ7iJG9bpxWKT3p45Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793057350; 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=OoFHaYBhm5BDHRt4hk2dDlai0Lu5WpyAocva34cAfYA=; b=upEET9uWfLzCTjdHb1OnoY6G6IqGN7mzr4HFQ9ww7FZCpyZf6QVvBCVEzvXn/C6aWPGa zFx6MCPI0QKSNxX3KvkAtQISpdfH+UoK52J+oV65MGh0PWEYHKlnfhgCcEUrEWZoyiwHb 7VMIMqLJ5/78fkodnemCBczZtwPt8o/SGV2Ebsiry1+K74kL6kpDli+zBydd8ZrqmW/nZ 5EpeFBm+zhiOVkuls87voAIPbLPTzmd/0ZRoHAYd1+vV5B8XUvnyZE8fPRNjv5MV7bHS0 9tFWbvkAEfqIj/w1zOycJQN+ZPT83UtnNB/qsRJtPak06as+m2gnRiNaFX4QokqOqgw== 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="UNbUEG/S"; 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 485EC606A31A; Mon, 26 Oct 2026 23:29:10 +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=UNbUEG/S Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0B0091F01825; Mon, 26 Oct 2026 23:28:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793057349; bh=OoFHaYBhm5BDHRt4hk2dDlai0Lu5WpyAocva34cAfYA=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=UNbUEG/SujRxvLabLs1Ob9p21oBhi+rGXvfUKjqMDQc12IUiZnwmTDApSDiN/doHK Htp9Ipsw+SQp+pFzIORI8kLx2XLdu4rOahJ0TPlelHfX1GJ1qLDkN8+N+aWCn8WCds tZKLfzo3kEI2Ic5a7yAs64WNXkp0GQ9463s7JB2V/ciJHVqOo5idW1iS2SKYE4l3o+ mmQ3vIfL+tDLHRHgEyxeKpggddER2NA819TKZnVHtRhi+Sq3NPEIiR5ET0FwgZX6ei fEZXbzJhICbnx1enS+A8NU5WTSrME8TXg/tsHJn7ecpC43Su1OH1tQwLJM8cp/lhBz YEOm5b5Nlxakg== From: "David Hildenbrand (Arm)" Date: Tue, 27 Oct 2026 00:17:56 +0100 Subject: [PATCH 36/46] mm: fix unkillable fault loop on MAP_DROPPABLE memory 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-v1-36-6f74bec9a5bb@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, Chris Mason , stable@vger.kernel.org, "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1689; i=david@kernel.org; h=from:subject:message-id; bh=pzxM/cFKO4VXQWnP1gi4l+XWqAOEVbNka7bwCiIYBW0=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLLu358ufnWFRtyuxz0v7f0W/Xstsp+rpij0whZOtoAdj O+fvJVI6ShlYRDjYJAVU2QJCr5v8PLlutpqNz5mmDmsTCBDGLg4BWAipR2MDJPYqpQSJzxd+VjV Sur4qftq4hcCTkXs/XHuWWzbsvvV/zwZGT7UT1FdZiUx0a1TNyc2/fYVjS1HumMsfZ2tf/o2Fkz IZgcA X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A From: Chris Mason handle_mm_fault() suppresses VM_FAULT_OOM for VM_DROPPABLE mappings. For user-mode faults, pending signals are processed before retrying the access. Kernel-mode faults on user buffers instead return directly to the faulting instruction. With persistent allocation failures (esp. memcg limits), a syscall, such as write(), can therefore loop while not dropping locks. Only suppress VM_FAULT_OOM when FAULT_FLAG_USER is set, allowing kernel-mode faults and GUP to fail and signal allocation errors. Fix generated by an LLM and sent by Chris Mason in private. Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings") Cc: stable@vger.kernel.org Signed-off-by: Chris Mason Reviewed-by: Lorenzo Stoakes (ARM) [ david: simplify description ] Signed-off-by: David Hildenbrand (Arm) --- mm/memory.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 5c5f326b8bcbe..230a2f4dafa13 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -6957,8 +6957,12 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address, lru_gen_exit_fault(); - /* If the mapping is droppable, then errors due to OOM aren't fatal. */ - if (is_droppable) + /* + * If the mapping is droppable, then errors due to OOM aren't fatal: the + * task returns to user mode, handles its signals and tries again. A + * fault from kernel mode has no such return, so it must see the error. + */ + if (is_droppable && (flags & FAULT_FLAG_USER)) ret &= ~VM_FAULT_OOM; if (flags & FAULT_FLAG_USER) { -- 2.43.0