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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A41F9C433EF for ; Tue, 2 Nov 2021 12:31:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8B31A60C51 for ; Tue, 2 Nov 2021 12:31:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231890AbhKBMdx (ORCPT ); Tue, 2 Nov 2021 08:33:53 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:36575 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231620AbhKBMdm (ORCPT ); Tue, 2 Nov 2021 08:33:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635856267; 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=7Mdxq38vDJ4XMLbX00dkdYRD7BHsLHxKYztHG08uvc0=; b=TOi0HMLmDTWZHC5mVHG1am+Fbrblg3VV3mrlHvGtsIFFwIlHXRGLksr5a8ECgpwGV5zRZ8 4yJmY7Qqwnpq54Ik/SfIiNoNhxn5QKeyYOVRGSThVW8tXSsTMo+D9DOGRkdJBFGJc20mBB nBop+qikztWwsghAJr6hz0aYGw+f5vg= 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-104-agWatDk_Pta2oHOwazM-pg-1; Tue, 02 Nov 2021 08:31:04 -0400 X-MC-Unique: agWatDk_Pta2oHOwazM-pg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C4282120C841; Tue, 2 Nov 2021 12:31:02 +0000 (UTC) Received: from max.localdomain (unknown [10.40.195.95]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7542919811; Tue, 2 Nov 2021 12:30:59 +0000 (UTC) From: Andreas Gruenbacher To: cluster-devel@redhat.com Cc: Linus Torvalds , Catalin Marinas , Alexander Viro , Christoph Hellwig , "Darrick J. Wong" , Paul Mackerras , Jan Kara , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com, kvm-ppc@vger.kernel.org, linux-btrfs@vger.kernel.org, Andreas Gruenbacher Subject: [PATCH v9 11/17] gfs2: Fix mmap + page fault deadlocks for buffered I/O Date: Tue, 2 Nov 2021 13:29:39 +0100 Message-Id: <20211102122945.117744-12-agruenba@redhat.com> In-Reply-To: <20211102122945.117744-1-agruenba@redhat.com> References: <20211102122945.117744-1-agruenba@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org In the .read_iter and .write_iter file operations, we're accessing user-space memory while holding the inode glock. There is a possibility that the memory is mapped to the same file, in which case we'd recurse on the same glock. We could detect and work around this simple case of recursive locking, but more complex scenarios exist that involve multiple glocks, processes, and cluster nodes, and working around all of those cases isn't practical or even possible. Avoid these kinds of problems by disabling page faults while holding the inode glock. If a page fault would occur, we either end up with a partial read or write or with -EFAULT if nothing could be read or written. In either case, we know that we're not done with the operation, so we indicate that we're willing to give up the inode glock and then we fault in the missing pages. If that made us lose the inode glock, we return a partial read or write. Otherwise, we resume the operation. This locking problem was originally reported by Jan Kara. Linus came up with the idea of disabling page faults. Many thanks to Al Viro and Matthew Wilcox for their feedback. Signed-off-by: Andreas Gruenbacher --- fs/gfs2/file.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 94 insertions(+), 5 deletions(-) diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c index 8f37e4bab995..d9126e3e6dd6 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 inline bool should_fault_in_pages(ssize_t ret, 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); + int pages = 1; + + if (likely(!count)) + return false; + if (ret <= 0 && ret != -EFAULT) + return false; + 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); + } + + *prev_count = count; + *window_size = (size_t)PAGE_SIZE * pages - offset_in_page(p); + return true; +} + static ssize_t gfs2_file_direct_read(struct kiocb *iocb, struct iov_iter *to, struct gfs2_holder *gh) { @@ -840,9 +870,17 @@ 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 indicate + * that the inode glock may be dropped, 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 +902,34 @@ 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 (should_fault_in_pages(ret, 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; @@ -885,8 +944,17 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, struct gfs2_inode *ip = GFS2_I(inode); struct gfs2_sbd *sdp = GFS2_SB(inode); struct gfs2_holder *statfs_gh = NULL; + 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 indicate + * that the inode glock may be dropped, fault in the pages manually, + * and retry. + */ + if (inode == sdp->sd_rindex) { statfs_gh = kmalloc(sizeof(*statfs_gh), GFP_NOFS); if (!statfs_gh) @@ -894,10 +962,11 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, } gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, gh); +retry: ret = gfs2_glock_nq(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); @@ -908,21 +977,41 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, } 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) + if (ret > 0) { iocb->ki_pos += ret; + read += ret; + } if (inode == sdp->sd_rindex) gfs2_glock_dq_uninit(statfs_gh); + if (should_fault_in_pages(ret, from, &prev_count, &window_size)) { + size_t leftover; + + gfs2_holder_allow_demote(gh); + leftover = fault_in_iov_iter_readable(from, window_size); + gfs2_holder_disallow_demote(gh); + if (leftover != window_size) { + if (!gfs2_holder_queued(gh)) { + if (read) + goto out_uninit; + goto retry; + } + goto retry_under_glock; + } + } out_unlock: - gfs2_glock_dq(gh); + if (gfs2_holder_queued(gh)) + gfs2_glock_dq(gh); out_uninit: gfs2_holder_uninit(gh); if (statfs_gh) kfree(statfs_gh); - return ret; + return read ? read : ret; } /** -- 2.31.1