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 X-Spam-Level: X-Spam-Status: No, score=-17.2 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_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C6002C4320A for ; Fri, 23 Jul 2021 20:59:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A57E960720 for ; Fri, 23 Jul 2021 20:59:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231829AbhGWUSh (ORCPT ); Fri, 23 Jul 2021 16:18:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:54369 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229530AbhGWUSa (ORCPT ); Fri, 23 Jul 2021 16:18:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1627073942; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ToHKBvWvBrc0+WOm0av91CBmkxfOIfNAK1a0+NJg6iY=; b=hOj/WcGaU21voYpA7YE2Jr3HCBpJIjNQWI96oFt+xPTOF2EBOeLxs0V/IKtsJqk/nQwevF uqKLhBe+g04ypU/SArmK5OkRvgQz+x7i3m4/UnN/PNkcKgXv6hc1RNALFq8d1oj3bCvJQo EQAZaTumsh8huKuRi4f9y86YJOQDM0o= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-167-Eo-FTJ3MPdK3ZrWqG8zDPw-1; Fri, 23 Jul 2021 16:58:58 -0400 X-MC-Unique: Eo-FTJ3MPdK3ZrWqG8zDPw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 151131853029; Fri, 23 Jul 2021 20:58:57 +0000 (UTC) Received: from max.com (unknown [10.40.194.164]) by smtp.corp.redhat.com (Postfix) with ESMTP id A7023100238C; Fri, 23 Jul 2021 20:58:54 +0000 (UTC) From: Andreas Gruenbacher To: Linus Torvalds , Alexander Viro , Christoph Hellwig , "Darrick J. Wong" Cc: Jan Kara , Matthew Wilcox , cluster-devel@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com, Andreas Gruenbacher Subject: [PATCH v3 3/7] gfs2: Fix mmap + page fault deadlocks for buffered I/O Date: Fri, 23 Jul 2021 22:58:36 +0200 Message-Id: <20210723205840.299280-4-agruenba@redhat.com> In-Reply-To: <20210723205840.299280-1-agruenba@redhat.com> References: <20210723205840.299280-1-agruenba@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In the .read_iter and .write_iter file operations, we're accessing user-space memory while holding the inodes glock. There's a possibility that the memory is mapped to the same file, in which case we'd recurse on the same glock. More complex scenarios can involve multiple glocks, processes, and even cluster nodes. Avoids these kinds of problems by disabling page faults while holding a glock. If a page fault occurs, we either end up with a partial read or write, or with -EFAULT if nothing could be read or written. In that case, we drop the glock, fault in the requested pages manually, and repeat the operation. This locking problem in gfs2 was originally reported by Jan Kara. Linus came up with the proposal to disable page faults. Many thanks to Al Viro and Matthew Wilcox for their feedback as well. Signed-off-by: Andreas Gruenbacher --- fs/gfs2/file.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c index 55ec1cadc9e6..f66ac7f56f6d 100644 --- a/fs/gfs2/file.c +++ b/fs/gfs2/file.c @@ -843,6 +843,12 @@ static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to) size_t written = 0; ssize_t ret; + /* + * In this function, we disable page faults when we're holding the + * inode glock while doing I/O. If a page fault occurs, we drop the + * inode glock, fault in the pages manually, and then we retry. + */ + if (iocb->ki_flags & IOCB_DIRECT) { ret = gfs2_file_direct_read(iocb, to, &gh); if (likely(ret != -ENOTBLK)) @@ -864,13 +870,19 @@ static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to) } ip = GFS2_I(iocb->ki_filp->f_mapping->host); gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh); +retry: ret = gfs2_glock_nq(&gh); if (ret) goto out_uninit; + pagefault_disable(); ret = generic_file_read_iter(iocb, to); + pagefault_enable(); if (ret > 0) written += ret; gfs2_glock_dq(&gh); + if (unlikely(iov_iter_count(to) && (ret > 0 || ret == -EFAULT)) && + fault_in_iov_iter(to)) + goto retry; out_uninit: gfs2_holder_uninit(&gh); return written ? written : ret; @@ -882,9 +894,20 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, struct iov_iter *fro struct inode *inode = file_inode(file); ssize_t ret; + /* + * In this function, we disable page faults when we're holding the + * inode glock while doing I/O. If a page fault occurs, we drop the + * inode glock, fault in the pages manually, and then we retry. + */ + +retry: current->backing_dev_info = inode_to_bdi(inode); + pagefault_disable(); ret = iomap_file_buffered_write(iocb, from, &gfs2_iomap_ops); + pagefault_enable(); current->backing_dev_info = NULL; + if (unlikely(ret == -EFAULT) && fault_in_iov_iter(from)) + goto retry; return ret; } -- 2.26.3