From mboxrd@z Thu Jan 1 00:00:00 1970 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 53A60C38A02 for ; Wed, 26 Oct 2022 02:03:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231164AbiJZCDr (ORCPT ); Tue, 25 Oct 2022 22:03:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229995AbiJZCDp (ORCPT ); Tue, 25 Oct 2022 22:03:45 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D271833E2A for ; Tue, 25 Oct 2022 19:03:44 -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 ams.source.kernel.org (Postfix) with ESMTPS id 8AD1FB81FDF for ; Wed, 26 Oct 2022 02:03:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 18FF2C433D6; Wed, 26 Oct 2022 02:03:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1666749822; bh=pptR85L0lYdLNV6IA0whrHErejm2dpCZHkStQ4ynRjE=; h=Date:To:From:Subject:From; b=xohL6P5+fGwFFcfA8oLtLhsu8WusJjj6UqJW08TN/tSbT4x6LP79walG/7lASGSPm sozS7IZ/X4TB81qszNmWMez+jYpv2PWlRaFt3jhXSmS/XbHguxwuBX/IfFWtJ2hBeb ji9cenVal2fekbpSXv5iU5DxdVvmIb8NTob/uMMU= Date: Tue, 25 Oct 2022 19:03:40 -0700 To: mm-commits@vger.kernel.org, willy@infradead.org, peterx@redhat.com, akpm@linux-foundation.org, aarcange@redhat.com, ira.weiny@intel.com, akpm@linux-foundation.org From: Andrew Morton Subject: + mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page-v2.patch added to mm-hotfixes-unstable branch Message-Id: <20221026020342.18FF2C433D6@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page-v2 has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page-v2.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page-v2.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Ira Weiny Subject: mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page-v2 Date: Tue, 25 Oct 2022 15:01:36 -0700 Update the commit message and comment based on additional discussion Thanks to Matt for pointing out the deadlock potential despite recursive reads. Link: https://lkml.kernel.org/r/20221025220136.2366143-1-ira.weiny@intel.com Signed-off-by: Ira Weiny Cc: Matthew Wilcox Cc: Andrew Morton Cc: Andrea Arcangeli Cc: Peter Xu Signed-off-by: Andrew Morton --- --- a/mm/userfaultfd.c~mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page-v2 +++ a/mm/userfaultfd.c @@ -159,9 +159,19 @@ static int mcopy_atomic_pte(struct mm_st page_kaddr = kmap_local_page(page); /* - * The mmap_lock is held here. Disable page faults to - * prevent deadlock should copy_from_user() fault. The - * copy will be retried outside the mmap_lock. + * The read mmap_lock is held here. Despite the + * mmap_lock being read recursive a deadlock is still + * possible if a writer has taken a lock. For example: + * + * process A thread 1 takes read lock on own mmap_lock + * process A thread 2 calls mmap, blocks taking write lock + * process B thread 1 takes page fault, read lock on own mmap lock + * process B thread 2 calls mmap, blocks taking write lock + * process A thread 1 blocks taking read lock on process B + * process B thread 1 blocks taking read lock on process A + * + * Disable page faults to prevent potential deadlock + * and retry the copy outside the mmap_lock. */ pagefault_disable(); ret = copy_from_user(page_kaddr, _ Patches currently in -mm which might be from ira.weiny@intel.com are mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page.patch mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page-v2.patch