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 X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 26C0EC5517A for ; Tue, 10 Nov 2020 04:20:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C453920781 for ; Tue, 10 Nov 2020 04:20:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="1iHe+xZR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731634AbgKJEUB (ORCPT ); Mon, 9 Nov 2020 23:20:01 -0500 Received: from mail.kernel.org ([198.145.29.99]:48582 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730520AbgKJEUB (ORCPT ); Mon, 9 Nov 2020 23:20:01 -0500 Received: from google.com (unknown [104.132.1.66]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8FB392068D; Tue, 10 Nov 2020 04:20:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604982000; bh=mtMkcnOFN4RlUUzRYrCLlt+g/UA6psyljz03o2ED1Wk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=1iHe+xZRrOfaeHxMTsyj7ALvSlQ+g1dAW1n+znRHzgrx6oY6IDpOepQtrbFD/7WDq dWa8dVV7NBTB7dd1uEvab2Kd+S5aq2PBmnhX1FdpopYa38kKl9VZuD5OvjWbklIkFZ LM9PUSrbXTbEHV2/tlTQgD1WptoYW/GgF1eq0aO4= Date: Mon, 9 Nov 2020 20:19:58 -0800 From: Jaegeuk Kim To: Chao Yu Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com, Light Hsieh Subject: Re: [f2fs-dev] [PATCH] f2fs: avoid race condition for shinker count Message-ID: <20201110041958.GA1598246@google.com> References: <20201109170012.2129411-1-jaegeuk@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/10, Chao Yu wrote: > On 2020/11/10 1:00, Jaegeuk Kim wrote: > > Light reported sometimes shinker gets nat_cnt < dirty_nat_cnt resulting in > > I didn't get the problem clearly, did you mean __count_nat_entries() will > give the wrong shrink count due to race condition? should there be a lock > while reading these two variables? > > > wrong do_shinker work. Basically the two counts should not happen like that. > > > > So, I suspect this race condtion where: > > - f2fs_try_to_free_nats __flush_nat_entry_set > > nat_cnt=2, dirty_nat_cnt=2 > > __clear_nat_cache_dirty > > spin_lock(nat_list_lock) > > list_move() > > spin_unlock(nat_list_lock) > > spin_lock(nat_list_lock) > > list_del() > > spin_unlock(nat_list_lock) > > nat_cnt=1, dirty_nat_cnt=2 > > nat_cnt=1, dirty_nat_cnt=1 > > nm_i->nat_cnt and nm_i->dirty_nat_cnt were protected by > nm_i->nat_tree_lock, I didn't see why expanding nat_list_lock range > will help... since there are still places nat_list_lock() didn't > cover these two reference counts. Yeah, I missed nat_tree_lock, and indeed it should cover this. So, the problem is Light reported subtle case of nat_cnt < dirty_nat_cnt in shrink_count. We may need to use nat_tree_lock in shrink_count? > > Thanks, > > > > > Reported-by: Light Hsieh > > Signed-off-by: Jaegeuk Kim > > --- > > fs/f2fs/node.c | 3 +-- > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c > > index 42394de6c7eb..e8ec65e40f06 100644 > > --- a/fs/f2fs/node.c > > +++ b/fs/f2fs/node.c > > @@ -269,11 +269,10 @@ static void __clear_nat_cache_dirty(struct f2fs_nm_info *nm_i, > > { > > spin_lock(&nm_i->nat_list_lock); > > list_move_tail(&ne->list, &nm_i->nat_entries); > > - spin_unlock(&nm_i->nat_list_lock); > > - > > set_nat_flag(ne, IS_DIRTY, false); > > set->entry_cnt--; > > nm_i->dirty_nat_cnt--; > > + spin_unlock(&nm_i->nat_list_lock); > > } > > static unsigned int __gang_lookup_nat_set(struct f2fs_nm_info *nm_i, > >