From patchwork Thu Sep 24 05:59:58 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Li, Hao" X-Patchwork-Id: 11796223 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 743B992C for ; Thu, 24 Sep 2020 06:00:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 586F4235FD for ; Thu, 24 Sep 2020 06:00:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726828AbgIXGAG (ORCPT ); Thu, 24 Sep 2020 02:00:06 -0400 Received: from mail.cn.fujitsu.com ([183.91.158.132]:41129 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726799AbgIXGAG (ORCPT ); Thu, 24 Sep 2020 02:00:06 -0400 X-IronPort-AV: E=Sophos;i="5.77,296,1596470400"; d="scan'208";a="99567075" Received: from unknown (HELO cn.fujitsu.com) ([10.167.33.5]) by heian.cn.fujitsu.com with ESMTP; 24 Sep 2020 14:00:02 +0800 Received: from G08CNEXMBPEKD06.g08.fujitsu.local (unknown [10.167.33.206]) by cn.fujitsu.com (Postfix) with ESMTP id 0A1AF48990E8; Thu, 24 Sep 2020 14:00:01 +0800 (CST) Received: from G08CNEXCHPEKD06.g08.fujitsu.local (10.167.33.205) by G08CNEXMBPEKD06.g08.fujitsu.local (10.167.33.206) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 24 Sep 2020 13:59:58 +0800 Received: from localhost.localdomain (10.167.225.206) by G08CNEXCHPEKD06.g08.fujitsu.local (10.167.33.209) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Thu, 24 Sep 2020 13:59:58 +0800 From: Hao Li To: , CC: , , , , , Subject: [PATCH v2] fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set Date: Thu, 24 Sep 2020 13:59:58 +0800 Message-ID: <20200924055958.825515-1-lihao2018.fnst@cn.fujitsu.com> X-Mailer: git-send-email 2.28.0 MIME-Version: 1.0 X-yoursite-MailScanner-ID: 0A1AF48990E8.ADB91 X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: lihao2018.fnst@cn.fujitsu.com X-Spam-Status: No Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org If DCACHE_REFERENCED is set, fast_dput() will return true, and then retain_dentry() have no chance to check DCACHE_DONTCACHE. As a result, the dentry won't be killed and the corresponding inode can't be evicted. In the following example, the DAX policy can't take effects unless we do a drop_caches manually. # DCACHE_LRU_LIST will be set echo abcdefg > test.txt # DCACHE_REFERENCED will be set and DCACHE_DONTCACHE can't do anything xfs_io -c 'chattr +x' test.txt # Drop caches to make DAX changing take effects echo 2 > /proc/sys/vm/drop_caches What this patch does is preventing fast_dput() from returning true if DCACHE_DONTCACHE is set. Then retain_dentry() will detect the DCACHE_DONTCACHE and will return false. As a result, the dentry will be killed and the inode will be evicted. In this way, if we change per-file DAX policy, it will take effects automatically after this file is closed by all processes. I also add some comments to make the code more clear. Signed-off-by: Hao Li Reviewed-by: Jan Kara Reviewed-by: Ira Weiny --- v1 is split into two standalone patch as discussed in [1], and the first patch has been reviewed in [2]. This is the second patch. [1]: https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/ [2]: https://lore.kernel.org/linux-fsdevel/20200906214002.GI12131@dread.disaster.area/ fs/dcache.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/dcache.c b/fs/dcache.c index ea0485861d93..97e81a844a96 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -793,10 +793,17 @@ static inline bool fast_dput(struct dentry *dentry) * a reference to the dentry and change that, but * our work is done - we can leave the dentry * around with a zero refcount. + * + * Nevertheless, there are two cases that we should kill + * the dentry anyway. + * 1. free disconnected dentries as soon as their refcount + * reached zero. + * 2. free dentries if they should not be cached. */ smp_rmb(); d_flags = READ_ONCE(dentry->d_flags); - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | + DCACHE_DISCONNECTED | DCACHE_DONTCACHE; /* Nothing to do? Dropping the reference was all we needed? */ if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))