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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5BF64C433F5 for ; Tue, 4 Jan 2022 13:18:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229568AbiADNSN (ORCPT ); Tue, 4 Jan 2022 08:18:13 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:55048 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233375AbiADNSN (ORCPT ); Tue, 4 Jan 2022 08:18:13 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1C12D61426 for ; Tue, 4 Jan 2022 13:18:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EE805C36AE7; Tue, 4 Jan 2022 13:18:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1641302292; bh=YnMaCUMaN6MFS9SW5hsu5+kjGgZjuaZQH7Uhhs1C3Gg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=LtIDotKL3VLhomm+82i1sW3l066f/grL3B9XKtLTY0T6yApKTBaRXQpTye4wZ5g5Y /F0m/BxlGPQ7xYsM7qzh2E/eoUcLxiHhJDalfvIPmZ5TR+1vxCTXEe2+1a5blzUeh7 ggARx95Bcyy7aBDcvQ/fdEwB9uV70d70CfVlMuy8= Date: Tue, 4 Jan 2022 14:18:08 +0100 From: Greg KH To: Chao Yu Cc: stable@vger.kernel.org, jaegeuk@kernel.org, linux-f2fs-devel@lists.sourceforge.net, Yi Zhuang Subject: Re: [PATCH] f2fs: quota: fix potential deadlock Message-ID: References: <20220104130513.3077-1-chao@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220104130513.3077-1-chao@kernel.org> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Tue, Jan 04, 2022 at 09:05:13PM +0800, Chao Yu wrote: > commit a5c0042200b28fff3bde6fa128ddeaef97990f8d upstream. > > As Yi Zhuang reported in bugzilla: > > https://bugzilla.kernel.org/show_bug.cgi?id=214299 > > There is potential deadlock during quota data flush as below: > > Thread A: Thread B: > f2fs_dquot_acquire > down_read(&sbi->quota_sem) > f2fs_write_checkpoint > block_operations > f2fs_look_all > down_write(&sbi->cp_rwsem) > f2fs_quota_write > f2fs_write_begin > __do_map_lock > f2fs_lock_op > down_read(&sbi->cp_rwsem) > __need_flush_qutoa > down_write(&sbi->quota_sem) > > This patch changes block_operations() to use trylock, if it fails, > it means there is potential quota data updater, in this condition, > let's flush quota data first and then trylock again to check dirty > status of quota data. > > The side effect is: in heavy race condition (e.g. multi quota data > upaters vs quota data flusher), it may decrease the probability of > synchronizing quota data successfully in checkpoint() due to limited > retry time of quota flush. > > Fixes: db6ec53b7e03 ("f2fs: add a rw_sem to cover quota flag changes") > Cc: stable@vger.kernel.org # v5.3+ > Reported-by: Yi Zhuang > Signed-off-by: Chao Yu > Signed-off-by: Jaegeuk Kim > --- > fs/f2fs/checkpoint.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c > index 83e9bc0f91ff..7b0282724231 100644 > --- a/fs/f2fs/checkpoint.c > +++ b/fs/f2fs/checkpoint.c > @@ -1162,7 +1162,8 @@ static bool __need_flush_quota(struct f2fs_sb_info *sbi) > if (!is_journalled_quota(sbi)) > return false; > > - down_write(&sbi->quota_sem); > + if (!down_write_trylock(&sbi->quota_sem)) > + return true; > if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH)) { > ret = false; > } else if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR)) { > -- > 2.32.0 > What stable tree(s) is this for? thanks, greg k-h