From patchwork Wed Apr 6 18:09:19 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Catalin Marinas X-Patchwork-Id: 12804012 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9178FC4332F for ; Wed, 6 Apr 2022 19:45:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232290AbiDFTqy (ORCPT ); Wed, 6 Apr 2022 15:46:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231789AbiDFTpx (ORCPT ); Wed, 6 Apr 2022 15:45:53 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2E4CB1DE59B; Wed, 6 Apr 2022 11:09:28 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B891461C4B; Wed, 6 Apr 2022 18:09:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B317FC385A3; Wed, 6 Apr 2022 18:09:24 +0000 (UTC) From: Catalin Marinas To: Linus Torvalds , Andreas Gruenbacher , Josef Bacik Cc: Al Viro , Andrew Morton , Chris Mason , David Sterba , Will Deacon , linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 0/3] Avoid live-lock in btrfs fault-in+uaccess loop Date: Wed, 6 Apr 2022 19:09:19 +0100 Message-Id: <20220406180922.1522433-1-catalin.marinas@arm.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi, I finally got around to reviving this series. However, I simplified it from v2 and focussed on solving the btrfs search_ioctl() problem only: https://lore.kernel.org/r/20211201193750.2097885-1-catalin.marinas@arm.com The btrfs search_ioctl() function can potentially live-lock on arm64 with MTE enabled due to a fault_in_writeable() + copy_to_user_nofault() unbounded loop. The uaccess can fault in the middle of a page (MTE tag check fault) even if a prior fault_in_writeable() successfully wrote to the beginning of that page. The btrfs loop always restarts the fault-in loop from the beginning of the user buffer, hence the live-lock. The series introduces fault_in_subpage_writeable() together with the arm64 probing counterpart and the btrfs fix. I don't think with the current kernel anything other than btrfs search_ioctl() can live-lock. The buffered file I/O can already cope with current fault_in_*() + copy_*_user() loops (the uaccess makes progress). Direct I/O either goes via GUP + kernel mapping access (and memcpy() can't fault) or, if the user buffer is not PAGE aligned, it may fall back to buffered I/O. So we really only care about fault_in_writeable(), hence this simplified series. If at some point we'll need to address other places, we can expand the sub-page probing to the other fault_in_*() functions. Thanks. Catalin Marinas (3): mm: Add fault_in_subpage_writeable() to probe at sub-page granularity arm64: Add support for user sub-page fault probing btrfs: Avoid live-lock in search_ioctl() on hardware with sub-page faults arch/Kconfig | 7 +++++++ arch/arm64/Kconfig | 1 + arch/arm64/include/asm/mte.h | 1 + arch/arm64/include/asm/uaccess.h | 15 +++++++++++++++ arch/arm64/kernel/mte.c | 30 ++++++++++++++++++++++++++++++ fs/btrfs/ioctl.c | 7 ++++++- include/linux/pagemap.h | 1 + include/linux/uaccess.h | 22 ++++++++++++++++++++++ mm/gup.c | 29 +++++++++++++++++++++++++++++ 9 files changed, 112 insertions(+), 1 deletion(-)