From patchwork Tue Dec 8 18:42:41 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Goldwyn Rodrigues X-Patchwork-Id: 11959705 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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 E454CC4167B for ; Tue, 8 Dec 2020 20:54:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA1B323B03 for ; Tue, 8 Dec 2020 20:54:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729376AbgLHUyt (ORCPT ); Tue, 8 Dec 2020 15:54:49 -0500 Received: from mx2.suse.de ([195.135.220.15]:60732 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729314AbgLHUyW (ORCPT ); Tue, 8 Dec 2020 15:54:22 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 071B5AD09; Tue, 8 Dec 2020 18:42:49 +0000 (UTC) From: Goldwyn Rodrigues To: linux-btrfs@vger.kernel.org Cc: Goldwyn Rodrigues Subject: [PATCH 2/2] btrfs: Make btrfs_direct_write atomic with respect to inode_lock Date: Tue, 8 Dec 2020 12:42:41 -0600 Message-Id: X-Mailer: git-send-email 2.29.2 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org From: Goldwyn Rodrigues btrfs_direct_write() fallsback to buffered write in case btrfs is not able to perform or complete a direct I/O. During the fallback inode lock is unlocked and relocked. This does not guarantee the atomicity of the entire write since the lock can be acquired by another write between unlock and relock. __btrfs_buffered_write() is used to perform the write without locks or checks and called from btrfs_direct_write(). fa54fc76db94 ("btrfs: push inode locking and unlocking into buffered/direct write") Signed-off-by: Goldwyn Rodrigues --- fs/btrfs/file.c | 55 +++++++++++++++++++++++++++---------------------- 1 file changed, 30 insertions(+), 25 deletions(-) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 272660a8279f..03569fe20237 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1649,11 +1649,11 @@ static ssize_t btrfs_write_check(struct kiocb *iocb, struct iov_iter *from) return count; } -static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb, +static noinline ssize_t __btrfs_buffered_write(struct kiocb *iocb, struct iov_iter *i) { struct file *file = iocb->ki_filp; - loff_t pos; + loff_t pos = iocb->ki_pos; struct inode *inode = file_inode(file); struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); struct page **pages = NULL; @@ -1667,20 +1667,7 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb, bool only_release_metadata = false; bool force_page_uptodate = false; loff_t old_isize = i_size_read(inode); - unsigned int ilock_flags = 0; - - if (iocb->ki_flags & IOCB_NOWAIT) - ilock_flags |= BTRFS_ILOCK_TRY; - - ret = btrfs_inode_lock(inode, ilock_flags); - if (ret < 0) - return ret; - - ret = btrfs_write_check(iocb, i); - if (ret <= 0) - goto out; - pos = iocb->ki_pos; nrptrs = min(DIV_ROUND_UP(iov_iter_count(i), PAGE_SIZE), PAGE_SIZE / (sizeof(struct page *))); nrptrs = min(nrptrs, current->nr_dirtied_pause - current->nr_dirtied); @@ -1884,10 +1871,33 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb, iocb->ki_pos += num_written; } out: - btrfs_inode_unlock(inode, ilock_flags); return num_written ? num_written : ret; } +static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb, + struct iov_iter *i) +{ + struct inode *inode = file_inode(iocb->ki_filp); + unsigned int ilock_flags = 0; + ssize_t ret; + + if (iocb->ki_flags & IOCB_NOWAIT) + ilock_flags |= BTRFS_ILOCK_TRY; + + ret = btrfs_inode_lock(inode, ilock_flags); + if (ret < 0) + return ret; + + ret = btrfs_write_check(iocb, i); + if (ret <= 0) + goto out; + + ret = __btrfs_buffered_write(iocb, i); +out: + btrfs_inode_unlock(inode, ilock_flags); + return ret; +} + static ssize_t check_direct_IO(struct btrfs_fs_info *fs_info, const struct iov_iter *iter, loff_t offset) { @@ -1928,10 +1938,8 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) return err; err = btrfs_write_check(iocb, from); - if (err <= 0) { - btrfs_inode_unlock(inode, ilock_flags); + if (err <= 0) goto out; - } pos = iocb->ki_pos; /* @@ -1945,16 +1953,12 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) goto relock; } - if (check_direct_IO(fs_info, from, pos)) { - btrfs_inode_unlock(inode, ilock_flags); + if (check_direct_IO(fs_info, from, pos)) goto buffered; - } dio = __iomap_dio_rw(iocb, from, &btrfs_dio_iomap_ops, &btrfs_dio_ops, is_sync_kiocb(iocb)); - btrfs_inode_unlock(inode, ilock_flags); - if (IS_ERR_OR_NULL(dio)) { err = PTR_ERR_OR_ZERO(dio); if (err < 0 && err != -ENOTBLK) @@ -1970,7 +1974,7 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) buffered: pos = iocb->ki_pos; - written_buffered = btrfs_buffered_write(iocb, from); + written_buffered = __btrfs_buffered_write(iocb, from); if (written_buffered < 0) { err = written_buffered; goto out; @@ -1991,6 +1995,7 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) invalidate_mapping_pages(file->f_mapping, pos >> PAGE_SHIFT, endbyte >> PAGE_SHIFT); out: + btrfs_inode_unlock(inode, ilock_flags); return written ? written : err; }