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=1793306555; b=5FCaWWdjKH5oQ6ZhLNy9OqHB8V6YWNw0tWkV7NavvgxbK61VCun+NVvgRKqlK13vTEsh lN9TIVc+oN+4/ae+kJBoJKa2E2VkYZT1sswbMCvrcYKKgflo1K+KO0/HTiTmZtyRtCx8c rEuBeVlQIk9cZ5cT7IXhhmnCadiePuTPrC1OoSSaq30cyrRdJi+T3Tub0og9CWlQk+FD6 qo4W6tynHf2JUywHcK8oEE1G3m7FwwWmEcjTm4t9rdjMx+KbO74N/kvJMSsPTqekcxoAI 31jVAct0fhUEtKWk/6J576spRDPafCjKFIDnPi4TSNtoFXHmsM4/29N1zxDvvsFQmCw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793306555; 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=GzohAuTFTF3f/1hrG58iOYYkxgWAfRYzNd87kJom8ew=; b=TZAH8UyhLoP3HG5825mENMEjhdQluiVX9QRFkO30Nw41HA8K4pQVI8Logdrnp2ZA5UGq mvwusgBgzDvTyOvlpuqcQfWY8Q9seP5iszZBR14RZWWY+87YawzKetk8n/I8uV7E14a+S 0yNpDtxMfL65FK96kaz5mCRci9KcFgXZD1Od8SaeC9YnIGtc9L0qGzV6qNNfD0vPeMiVQ 8HHefL2p4FUTXYRCG6h3b/PNeIdGAZ/YwEmeQ5CYbA2xR4+4leSQFz1CegajwnugVbWKv Ek9NFEKcYByR0M4YoeyIQ4nQ7bkaRKOIkoUp2SCAO2bCgrL8POtoE0IoQ9z7vcXZhqQ== 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=odGKC4Xb; 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 26D11606A321; Thu, 29 Oct 2026 20:42:35 +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=odGKC4Xb Received: by smtp.kernel.org (Postfix) with ESMTPSA id 038A81F01816; Thu, 29 Oct 2026 20:42:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793306555; bh=GzohAuTFTF3f/1hrG58iOYYkxgWAfRYzNd87kJom8ew=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=odGKC4XbmYtEAL0Gbsmsvx/WY4VvPYy77ntTduDNGVxTee9x8eCFs1dlirZrbm7zy iC+kt5OPi0b7fGJlGk807OCvIbOWr/Z78TV/dFDtdfnfrPq2aHFVXyMPhLCSOvB1Y2 ZrN4hFhr9U2G7pJPJRhXKDaX8gWNjGlvbNVUoesFXn/q0rr+u58Qom2mW6f0Q09dKe 3q0AyCRIpFeQddnbKDlVIMB1qh/ZQ3BtSWnCL5WPB7IN9/D8mom8vqt7yZu9Csa5jg BDnVwDUFvXRY6YrP7saZiBtyJiwIROc+tG9ELKoNHPe8loZEUzoVScdiDJdLpehZRi /RsACXHCoLgfQ== From: "David Hildenbrand (Arm)" Date: Thu, 29 Oct 2026 21:33:32 +0100 Subject: [PATCH v2 37/47] 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: <20261029-fixes_core-v2-37-a64ce7f83abb@kernel.org> References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> In-Reply-To: <20261029-fixes_core-v2-0-a64ce7f83abb@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=1687; i=david@kernel.org; h=from:subject:message-id; bh=yoxwQ2Y6qIbeUiwHGT1Y0HumpGAEonmZ/vQerxKuLzY=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIer+3czvM5O0THx//vtoUbudj7mWSPupTa/Tnr4Jkd8 Tn+Vk51RykLgxgHg6yYIktQ8H2Dly/X1Va78THDzGFlAhnCwMUpABNZl8XI8FEnafGyvrx5M6Kn sCw4PefgS4/ySwEXYgxE4k5desdXsorhf+JjyZr1Ze+2Bc4VtlpxsJI/8JO19IGImflnzH06jdO qmAE= 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 732b8f926de6..77d4bbf444bc 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