From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 135B6606A32C for ; Thu, 29 Oct 2026 11:06:31 +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=DG5qlG+6 Received: by kanga.kvack.org (Postfix) id 410326B00EF; Thu, 29 Oct 2026 07:06:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3C0F46B05B1; Thu, 29 Oct 2026 07:06:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2892B6B05B5; Thu, 29 Oct 2026 07:06:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 0196E6B00EF for ; Thu, 29 Oct 2026 07:06:29 -0400 (EDT) Received: from smtpin30.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id B0409403AD for ; Thu, 29 Oct 2026 11:06:27 +0000 (UTC) X-FDA: 85375385214.30.9F0DB16 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf01.hostedemail.com (Postfix) with ESMTP id E372240010 for ; Thu, 29 Oct 2026 11:06:25 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=DG5qlG+6; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf01.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793271985; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=G4SI2MOIEpxP5HU3ERLaWsdHJtIDnixVPHVu+nHUwyQ=; b=T9FOhPjCkHAShkKzDO8J67hICJfwjol7Nt/2w56oFFTGoN82PRMx8WRkk3YRYksLyjJtNs PewqcMaH0THVIPlkNc8tZ4wUBa0h+wF71ohzgPuvv8SMKNzwyyWxM/ztgirNa1l5XnGYp/ KoTrWNmpBHvIM91iMH0GFnQGmKhSYXo= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=DG5qlG+6; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf01.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793271985; b=pDyzOXgZ9HPAf3d2tAg/k5pcOHMBIy3dnT3SZayhsJIevzpUVRiK70840lFndgyZI8gzr4 k2y5w2baGOUG4AEjOoVDeGYDoTPSUP+26zHZkSy5K4mU0Tc74dsGwaQlpwtZhmkZTflc3R jpvgFh+4QnFSVRot3lwlc8if/RCESmY= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 16B53600D1; Thu, 29 Oct 2026 11:06:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7D77C1F01825; Thu, 29 Oct 2026 11:06:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793271983; bh=G4SI2MOIEpxP5HU3ERLaWsdHJtIDnixVPHVu+nHUwyQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=DG5qlG+6Sja3SZ5kFUK34tgk4SYB6mT49t9Ydiwl1UmmUSD3Z7eZTpdi9hErSp6J3 rJy+pdJ4xnrv+lAE+8PJM9LuhQ91KO44IKjD6i7lRiQF5sAG6yfA42ECErt9i+4hlZ VqUZ+q8IKKTOoKoRg0gz3v3YNhG4U3iakSFkuH5T2JEkY20iTWI+uTLXikjQQRHGFM iitTQcffWyPVBKOk5dKhoqgHt5X5LmnO9yty8zuvAujX+5k++YqHcbVx84qeghojpP ONGbbquOo1zaFCKZkU54MNJA/SW+jdnu2TfP3rM7xp551okzH9jzB8lL389t/PCYJF RNML/haAtaDfA== Message-ID: <676e49b1-6cc0-4d0a-8492-452ffb294d2a@kernel.org> Date: Thu, 29 Oct 2026 12:06:02 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 36/46] mm: fix unkillable fault loop on MAP_DROPPABLE memory 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 , Johannes Weiner , Shakeel Butt , Michal Hocko , Roman Gushchin 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 References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-36-6f74bec9a5bb@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E372240010 X-Stat-Signature: iu6hgj5nkmx7e5qx8nfgayjkimg4cfd9 X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793271985-128203 X-HE-Meta: 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 4TCIUL1U ruUXnmDm8ToLlVw1eNIJy7alsuWFvcmJX3+krdSuciGe7dT6wDC60g4V9ZzFiVb1Hy94Q8DRgIM5lMqqm4/9o6808yMz+Ex3SPTY6q0Paa2gm4YvMBlP/kcO4KRJYoFfh9NsBk1zGESTnFOaJXfCRrdn7Ulqmg3kguDIK8WhRR9gCA0mlAaZ4bTyhnvKLxlR3xWrST7PNQsvUHsvFO/XPbglAY155bRbHas20a/soDmtzVme5YxHdS01auyJINA6e0i4gkw9ei/3AIEN9b8yAVUM1HOTIjTumnSdh9TB1D/1Mf5RTZI+fA9MliEfLCUCDocbZDbk/U2znwbRUtKyGe0voT8PqzHeQuirymjmJrQ+M4LfCE7PIW+RJUz4dgCgImTidNBvyxn3WlC/sQWGTl5wa5A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/27/26 00:17, David Hildenbrand (Arm) wrote: > 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) { > I think this is the single patch in here where I struggle with the side-effects and possibly remaining issues for user faults. It feels like the obviously right thing to do, but it all feels a bit shaky. Maybe the memcg/reclaim folks have a better understanding of this? -- Cheers, David