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=-16.5 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 C5FE4C43214 for ; Thu, 19 Aug 2021 19:42:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AD43B60EBD for ; Thu, 19 Aug 2021 19:42:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235378AbhHSTml (ORCPT ); Thu, 19 Aug 2021 15:42:41 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:56311 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235328AbhHSTmh (ORCPT ); Thu, 19 Aug 2021 15:42:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1629402120; 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=1XWuyMTj+hy427MD7LC7x2B24g+i8ekxZt//CLsVy4g=; b=YpVbbmEUdKeHHHDPLegYTHzmAxpUXwtG/iX15VctuQ/q/FxIgSPsNdTe5CDoMbe4cB7hKY ZLXhGKAvtxMb/STd3Pn3e3n77YLk/wnph6hn3BdhXgfztx79S8Xb0HILqqXU3jW9euP/h2 FUcy4+a5BCrzgvO8Esy24ovI1B4e5M0= 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-380-BlzBVgWhNvaG1TWQzD2q2Q-1; Thu, 19 Aug 2021 15:41:57 -0400 X-MC-Unique: BlzBVgWhNvaG1TWQzD2q2Q-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B36AA87D542; Thu, 19 Aug 2021 19:41:55 +0000 (UTC) Received: from max.com (unknown [10.40.194.206]) by smtp.corp.redhat.com (Postfix) with ESMTP id 36EFB60938; Thu, 19 Aug 2021 19:41:53 +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 v6 12/19] gfs2: Fix mmap + page fault deadlocks for buffered I/O Date: Thu, 19 Aug 2021 21:40:55 +0200 Message-Id: <20210819194102.1491495-13-agruenba@redhat.com> In-Reply-To: <20210819194102.1491495-1-agruenba@redhat.com> References: <20210819194102.1491495-1-agruenba@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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 indicate that we're willing to give up the glock, fault in the requested pages manually, and repeat the operation. This kind of 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. Signed-off-by: Andreas Gruenbacher --- fs/gfs2/file.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 93 insertions(+), 5 deletions(-) diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c index 813154d60834..c4262d6ba5e4 100644 --- a/fs/gfs2/file.c +++ b/fs/gfs2/file.c @@ -776,6 +776,36 @@ static int gfs2_fsync(struct file *file, loff_t start, loff_t end, return ret ? ret : ret1; } +static bool should_fault_in_pages(struct iov_iter *i, size_t *prev_count, + size_t *window_size) +{ + char __user *p = i->iov[0].iov_base + i->iov_offset; + size_t count = iov_iter_count(i); + size_t size; + + if (!iter_is_iovec(i)) + return false; + + if (*prev_count != count || !*window_size) { + int pages, nr_dirtied; + + pages = min_t(int, BIO_MAX_VECS, + DIV_ROUND_UP(iov_iter_count(i), PAGE_SIZE)); + nr_dirtied = max(current->nr_dirtied_pause - + current->nr_dirtied, 1); + pages = min(pages, nr_dirtied); + size = (size_t)PAGE_SIZE * pages - offset_in_page(p); + } else { + size = (size_t)PAGE_SIZE - offset_in_page(p); + if (*window_size <= size) + return false; + } + + *prev_count = count; + *window_size = size; + return true; +} + static ssize_t gfs2_file_direct_read(struct kiocb *iocb, struct iov_iter *to, struct gfs2_holder *gh) { @@ -840,9 +870,16 @@ static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to) { struct gfs2_inode *ip; struct gfs2_holder gh; + size_t prev_count = 0, window_size = 0; 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 retry. + */ + if (iocb->ki_flags & IOCB_DIRECT) { ret = gfs2_file_direct_read(iocb, to, &gh); if (likely(ret != -ENOTBLK)) @@ -864,13 +901,35 @@ 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; +retry_under_glock: + 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)) && + should_fault_in_pages(to, &prev_count, &window_size)) { + size_t leftover; + + gfs2_holder_allow_demote(&gh); + leftover = fault_in_iov_iter_writeable(to, window_size); + gfs2_holder_disallow_demote(&gh); + if (leftover != window_size) { + if (!gfs2_holder_queued(&gh)) { + if (written) + goto out_uninit; + goto retry; + } + goto retry_under_glock; + } + } + if (gfs2_holder_queued(&gh)) + gfs2_glock_dq(&gh); out_uninit: gfs2_holder_uninit(&gh); return written ? written : ret; @@ -882,13 +941,22 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, struct iov_iter *fro struct inode *inode = file_inode(file); struct gfs2_inode *ip = GFS2_I(inode); struct gfs2_sbd *sdp = GFS2_SB(inode); + size_t prev_count = 0, window_size = 0; + size_t read = 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 retry. + */ + gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, &ip->i_gh); +retry: ret = gfs2_glock_nq(&ip->i_gh); if (ret) goto out_uninit; - +retry_under_glock: if (inode == sdp->sd_rindex) { struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode); @@ -899,20 +967,40 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, struct iov_iter *fro } 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 (ret > 0) + read += ret; if (inode == sdp->sd_rindex) { struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode); gfs2_glock_dq_uninit(&m_ip->i_gh); } - + if (unlikely(iov_iter_count(from) && (ret > 0 || ret == -EFAULT)) && + should_fault_in_pages(from, &prev_count, &window_size)) { + size_t leftover; + + gfs2_holder_allow_demote(&ip->i_gh); + leftover = fault_in_iov_iter_readable(from, window_size); + gfs2_holder_disallow_demote(&ip->i_gh); + if (leftover != window_size) { + if (!gfs2_holder_queued(&ip->i_gh)) { + if (read) + goto out_uninit; + goto retry; + } + goto retry_under_glock; + } + } out_unlock: - gfs2_glock_dq(&ip->i_gh); + if (gfs2_holder_queued(&ip->i_gh)) + gfs2_glock_dq(&ip->i_gh); out_uninit: gfs2_holder_uninit(&ip->i_gh); - return ret; + return read ? read : ret; } /** -- 2.26.3