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 CF7E0EB64D7 for ; Mon, 26 Jun 2023 13:10:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230023AbjFZNKG (ORCPT ); Mon, 26 Jun 2023 09:10:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57682 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229481AbjFZNKE (ORCPT ); Mon, 26 Jun 2023 09:10:04 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8E699B9; Mon, 26 Jun 2023 06:10:03 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 3A4031F8AB; Mon, 26 Jun 2023 13:10:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1687785002; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=p6JfJgn7WigU75C2F7rQV1RIBlnMRsvyrWJCIdw/dCA=; b=eys9iBcHZeEhwoM+4xJcArAsNTJEoZ4F5/JuvySgzA6lig0YQ2tKBwmhJgJeGuTKW0ojic uU6ctK6n8OkxZ1BPLsNhpVVwGfa3dN5NOYQdiORfGNJsaHjXve08g9PgKOjHS89z+XuLtS G20EEJ5kA0P7k0HkW1y/WVHUf7dDKB8= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1687785002; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=p6JfJgn7WigU75C2F7rQV1RIBlnMRsvyrWJCIdw/dCA=; b=VXWH/ebYmCkoxq1Jrdwc3zdPADBQ/c6B+J2fQ2Otd4ECu7PfiGlen3urUdNidZRR7g2tvt zOaSHX36FGPHZwAQ== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 9D9F613483; Mon, 26 Jun 2023 13:10:01 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id hTf9JSmOmWQaXgAAMHmgww (envelope-from ); Mon, 26 Jun 2023 13:10:01 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id 472B1A0754; Mon, 26 Jun 2023 15:09:57 +0200 (CEST) Date: Mon, 26 Jun 2023 15:09:57 +0200 From: Jan Kara To: Baokun Li Cc: Jan Kara , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, yangerkun@huawei.com, chengzhihao1@huawei.com, yukuai3@huawei.com Subject: Re: [PATCH] quota: fix race condition between dqput() and dquot_mark_dquot_dirty() Message-ID: <20230626130957.kvfli23djxc2opkq@quack3> References: <20230616085608.42435-1-libaokun1@huawei.com> <20230616152824.ndpgvkegvvip2ahh@quack3> <20230622145620.hk3bdjxtlr64gtzl@quack3> 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-ext4@vger.kernel.org Hello! On Sun 25-06-23 15:56:10, Baokun Li wrote: > > > I think we can simply focus on the race between the DQ_ACTIVE_B flag and > > > the DQ_MOD_B flag, which is the core problem, because the same quota > > > should not have both flags. These two flags are protected by dq_list_lock > > > and dquot->dq_lock respectively, so it makes sense to add a > > > wait_on_dquot() to ensure the accuracy of DQ_ACTIVE_B. > > But the fundamental problem is not only the race with DQ_MOD_B setting. The > > dquot structure can be completely freed by the time > > dquot_claim_space_nodirty() calls dquot_mark_dquot_dirty() on it. That's > > why I think making __dquot_transfer() obey dquot_srcu rules is the right > > solution. > Yes, now I also think that making __dquot_transfer() obey dquot_srcu > rules is a better solution. But with inode->i_lock protection, why would > the dquot structure be completely freed? Well, when dquot_claim_space_nodirty() calls mark_all_dquot_dirty() it does not hold any locks (only dquot_srcu). So nothing prevents dquot_transfer() to go, swap dquot structure pointers and drop dquot references and after that mark_all_dquot_dirty() can use a stale pointer to call mark_dquot_dirty() on already freed memory. Honza -- Jan Kara SUSE Labs, CR