From patchwork Mon Jul 13 03:33:30 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 11658649 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 909D9138C for ; Mon, 13 Jul 2020 03:35:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 726B320722 for ; Mon, 13 Jul 2020 03:35:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594611305; bh=41IYY+/hX2sb2b1GBvHrVsrCwrGfmHuoNNwcohgG4Us=; h=From:To:Cc:Subject:Date:List-ID:From; b=xpS8UkEt23dbs1v4+8k8vsf0bLIAX88HkOVkLRNRdzLlluE+78hFV6EPrbKYiV+GE VP1g+RXyuxUNE80DuoB5t/6s1p2Lw+//E00THsrsCwR0XgHsFP6rWaWpLVTv/rOlnO sz7DdYrvLrTfYwRlI/VS0WMSLWCBLoigcrfPklz0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728252AbgGMDfE (ORCPT ); Sun, 12 Jul 2020 23:35:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:47574 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726491AbgGMDfE (ORCPT ); Sun, 12 Jul 2020 23:35:04 -0400 Received: from sol.hsd1.ca.comcast.net (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7D2E320722; Mon, 13 Jul 2020 03:35:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594611303; bh=41IYY+/hX2sb2b1GBvHrVsrCwrGfmHuoNNwcohgG4Us=; h=From:To:Cc:Subject:Date:From; b=zKLykD+ebs0yY0QSgcLifTmGtf0olv8jsDAubALRq2trmmLiErvOdj5Lt9Q5pktgz UerZhze4E3Z8Vnq8R++twoa81O8L6/XVIA6/7fKEO0o0KQBh9sBm7yvNt/Xd4/ZOtB J3u9YYUlHTWNLZLawnI+60HlK4L2C0qCxnhIAL2w= From: Eric Biggers To: linux-fsdevel@vger.kernel.org Cc: linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org Subject: [PATCH] fs/direct-io: avoid data race on ->s_dio_done_wq Date: Sun, 12 Jul 2020 20:33:30 -0700 Message-Id: <20200713033330.205104-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org From: Eric Biggers Fix the preliminary checks for ->s_dio_done_wq to use READ_ONCE(), since it's a data race, and technically the behavior is undefined without READ_ONCE(). Also, on one CPU architecture (Alpha), the data read dependency barrier included in READ_ONCE() is needed to guarantee that the pointed-to struct is seen as fully initialized. Signed-off-by: Eric Biggers --- fs/direct-io.c | 8 +++----- fs/internal.h | 9 ++++++++- fs/iomap/direct-io.c | 3 +-- 3 files changed, 12 insertions(+), 8 deletions(-) diff --git a/fs/direct-io.c b/fs/direct-io.c index 6d5370eac2a8..26221ae24156 100644 --- a/fs/direct-io.c +++ b/fs/direct-io.c @@ -590,7 +590,7 @@ static inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio) * filesystems that don't need it and also allows us to create the workqueue * late enough so the we can include s_id in the name of the workqueue. */ -int sb_init_dio_done_wq(struct super_block *sb) +int __sb_init_dio_done_wq(struct super_block *sb) { struct workqueue_struct *old; struct workqueue_struct *wq = alloc_workqueue("dio/%s", @@ -615,9 +615,7 @@ static int dio_set_defer_completion(struct dio *dio) if (dio->defer_completion) return 0; dio->defer_completion = true; - if (!sb->s_dio_done_wq) - return sb_init_dio_done_wq(sb); - return 0; + return sb_init_dio_done_wq(sb); } /* @@ -1250,7 +1248,7 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode, retval = 0; if (iocb->ki_flags & IOCB_DSYNC) retval = dio_set_defer_completion(dio); - else if (!dio->inode->i_sb->s_dio_done_wq) { + else { /* * In case of AIO write racing with buffered read we * need to defer completion. We can't decide this now, diff --git a/fs/internal.h b/fs/internal.h index 9b863a7bd708..6736c9eee978 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -178,7 +178,14 @@ extern void mnt_pin_kill(struct mount *m); extern const struct dentry_operations ns_dentry_operations; /* direct-io.c: */ -int sb_init_dio_done_wq(struct super_block *sb); +int __sb_init_dio_done_wq(struct super_block *sb); +static inline int sb_init_dio_done_wq(struct super_block *sb) +{ + /* pairs with cmpxchg() in __sb_init_dio_done_wq() */ + if (likely(READ_ONCE(sb->s_dio_done_wq))) + return 0; + return __sb_init_dio_done_wq(sb); +} /* * fs/stat.c: diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c index ec7b78e6feca..dc7fe898dab8 100644 --- a/fs/iomap/direct-io.c +++ b/fs/iomap/direct-io.c @@ -487,8 +487,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, dio_warn_stale_pagecache(iocb->ki_filp); ret = 0; - if (iov_iter_rw(iter) == WRITE && !wait_for_completion && - !inode->i_sb->s_dio_done_wq) { + if (iov_iter_rw(iter) == WRITE && !wait_for_completion) { ret = sb_init_dio_done_wq(inode->i_sb); if (ret < 0) goto out_free_dio;