From patchwork Wed Jun 12 17:24:08 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Amir Goldstein X-Patchwork-Id: 10990485 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id CDF721515 for ; Wed, 12 Jun 2019 17:24:20 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B35CD28A8E for ; Wed, 12 Jun 2019 17:24:20 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id A4A8728A95; Wed, 12 Jun 2019 17:24:20 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 13E7328A99 for ; Wed, 12 Jun 2019 17:24:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407290AbfFLRYT (ORCPT ); Wed, 12 Jun 2019 13:24:19 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:40390 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407019AbfFLRYS (ORCPT ); Wed, 12 Jun 2019 13:24:18 -0400 Received: by mail-wr1-f67.google.com with SMTP id p11so17799039wre.7; Wed, 12 Jun 2019 10:24:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=JaDk0B2JuZF4UPbktkuAfxaGadSzIqD38JFVgmfBIWs=; b=L/8aQM0zZfjRGpclojJSpYbbgU7RKIEziz0NHfsIDDLYRDOt+iAy7LlpErcteY5hbk Zk8xPd24vIzJ+HhiWHf5i+cHYyroTfaPCN6cDKDlObpRb4pyOAqhEeXfMbxz2zEYK37M uZ43tQodaOLP8QEgDQNgtY/bk3mtv2/hYCwHAYIQydD2iLFAJJZTvRvFwyJRR1vokBFr UQbGJLErLOZIkSPuzDj91DHtrPsJR8Wmd6XlLiEx/bgS5aBrH8Pz6kOdPULmMaDjiPHB 0gOFBLuMleWHilRh4Cz5vJTOrjRvlbr1USqXgrhDH9kAWBcHXywc+LKzzfF8HsY2iXpv 9JUQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=JaDk0B2JuZF4UPbktkuAfxaGadSzIqD38JFVgmfBIWs=; b=RWSpmAFULhfjhDFG7/5HQT4w8K9zyIrmAjqBJn6Qrd1Mi6rI0oScPptxcOrkQ6wrBH PjoM6OZjJglAJmFDWw4MdXhtuoP0mDlW4TAYC8TxRcYdBSgrZRsuoJZVwImDN8LzRvWi jKACR399hoSwseoKIuE1bvzCFaX7lzT95NpgL2P26OCi6Zv9csvMjjEIPmgomUiys9Po n951D6N105xVj6mUl7jv/XmCjEfep5sbFEkLUaL0xqDMTBdDVg3He8Cy2r1SZNYkwjcQ Bva2Q5pTlLc7/NfaROiH8ZMqc3K4/6eDXZTW6rO2Ik7tI5PMGUXTCzXX01xuh4kTl8DW /pCQ== X-Gm-Message-State: APjAAAXf13JyBGlJxxt+Vd4d1v5SXh55wOowFNzBdPYJU3G49XFcmY5W dvpiBC4jjfmhN7MmzVYOD3U= X-Google-Smtp-Source: APXvYqwStm/z+FAde/SFAgWzsa5IoAKISOCAtEsvi1y9UO+FcQKU4hEaIb9WOUjr2yY/00ILxAJHyw== X-Received: by 2002:a5d:6b47:: with SMTP id x7mr3863898wrw.83.1560360255667; Wed, 12 Jun 2019 10:24:15 -0700 (PDT) Received: from localhost.localdomain ([5.102.238.208]) by smtp.gmail.com with ESMTPSA id j17sm423482wrw.6.2019.06.12.10.24.14 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 12 Jun 2019 10:24:14 -0700 (PDT) From: Amir Goldstein To: Miklos Szeredi , Jeff Layton , "J . Bruce Fields" Cc: linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-unionfs@vger.kernel.org Subject: [PATCH v2] locks: eliminate false positive conflicts for write lease Date: Wed, 12 Jun 2019 20:24:08 +0300 Message-Id: <20190612172408.22671-1-amir73il@gmail.com> X-Mailer: git-send-email 2.17.1 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP check_conflicting_open() is checking for existing fd's open for read or for write before allowing to take a write lease. The check that was implemented using i_count and d_count is an approximation that has several false positives. For example, overlayfs since v4.19, takes an extra reference on the dentry; An open with O_PATH takes a reference on the dentry although the file cannot be read nor written. Change the implementation to use i_readcount and i_writecount to eliminate the false positive conflicts and allow a write lease to be taken on an overlayfs file. The change of behavior with existing fd's open with O_PATH is symmetric w.r.t. current behavior of lease breakers - an open with O_PATH currently does not break a write lease. This increases the size of struct inode by 4 bytes on 32bit archs when CONFIG_FILE_LOCKING is defined and CONFIG_IMA was not already defined. Cc: # v4.19 Signed-off-by: Amir Goldstein Signed-off-by: Amir Goldstein Signed-off-by: Amir Goldstein --- Miklos, Jeff and Bruce, This patch fixes a v4.19 overlayfs regression with taking write leases. It also provides correct semantics w.r.t RDONLY open counter that Bruce also needed for nfsd. Since this is locks code that fixes an overlayfs regression which is also needed for nfsd, it could go via either of your trees. I didn't want to pick sides, so first one to grab the patch wins ;-) I verified the changes using modified LTP F_SETLEASE tests [1], which I ran over xfs and overlayfs. Thanks, Amir. [1] https://github.com/amir73il/ltp/commits/overlayfs-devel Changes since v1: - Drop patch to fold i_readcount into i_count - Make i_readcount depend on CONFIG_FILE_LOCKING fs/locks.c | 33 ++++++++++++++++++++++----------- include/linux/fs.h | 4 ++-- 2 files changed, 24 insertions(+), 13 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index ec1e4a5df629..28528b4fc53b 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -1753,10 +1753,10 @@ int fcntl_getlease(struct file *filp) } /** - * check_conflicting_open - see if the given dentry points to a file that has + * check_conflicting_open - see if the given file points to an inode that has * an existing open that would conflict with the * desired lease. - * @dentry: dentry to check + * @filp: file to check * @arg: type of lease that we're trying to acquire * @flags: current lock flags * @@ -1764,19 +1764,31 @@ int fcntl_getlease(struct file *filp) * conflict with the lease we're trying to set. */ static int -check_conflicting_open(const struct dentry *dentry, const long arg, int flags) +check_conflicting_open(struct file *filp, const long arg, int flags) { int ret = 0; - struct inode *inode = dentry->d_inode; + struct inode *inode = locks_inode(filp); + int wcount = atomic_read(&inode->i_writecount); + int self_wcount = 0, self_rcount = 0; if (flags & FL_LAYOUT) return 0; - if ((arg == F_RDLCK) && inode_is_open_for_write(inode)) + if (arg == F_RDLCK && wcount > 0) return -EAGAIN; - if ((arg == F_WRLCK) && ((d_count(dentry) > 1) || - (atomic_read(&inode->i_count) > 1))) + /* Eliminate deny writes from actual writers count */ + if (wcount < 0) + wcount = 0; + + /* Make sure that only read/write count is from lease requestor */ + if (filp->f_mode & FMODE_WRITE) + self_wcount = 1; + else if ((filp->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) + self_rcount = 1; + + if (arg == F_WRLCK && (wcount != self_wcount || + atomic_read(&inode->i_readcount) != self_rcount)) ret = -EAGAIN; return ret; @@ -1786,8 +1798,7 @@ static int generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **priv) { struct file_lock *fl, *my_fl = NULL, *lease; - struct dentry *dentry = filp->f_path.dentry; - struct inode *inode = dentry->d_inode; + struct inode *inode = locks_inode(filp); struct file_lock_context *ctx; bool is_deleg = (*flp)->fl_flags & FL_DELEG; int error; @@ -1822,7 +1833,7 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr percpu_down_read(&file_rwsem); spin_lock(&ctx->flc_lock); time_out_leases(inode, &dispose); - error = check_conflicting_open(dentry, arg, lease->fl_flags); + error = check_conflicting_open(filp, arg, lease->fl_flags); if (error) goto out; @@ -1879,7 +1890,7 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr * precedes these checks. */ smp_mb(); - error = check_conflicting_open(dentry, arg, lease->fl_flags); + error = check_conflicting_open(filp, arg, lease->fl_flags); if (error) { locks_unlink_lock_ctx(lease); goto out; diff --git a/include/linux/fs.h b/include/linux/fs.h index 79ffa2958bd8..2d55f1b64014 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -694,7 +694,7 @@ struct inode { atomic_t i_count; atomic_t i_dio_count; atomic_t i_writecount; -#ifdef CONFIG_IMA +#if defined(CONFIG_IMA) || defined(CONFIG_FILE_LOCKING) atomic_t i_readcount; /* struct files open RO */ #endif union { @@ -2895,7 +2895,7 @@ static inline bool inode_is_open_for_write(const struct inode *inode) return atomic_read(&inode->i_writecount) > 0; } -#ifdef CONFIG_IMA +#if defined(CONFIG_IMA) || defined(CONFIG_FILE_LOCKING) static inline void i_readcount_dec(struct inode *inode) { BUG_ON(!atomic_read(&inode->i_readcount));