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 263A2ECAAD3 for ; Wed, 14 Sep 2022 09:01:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229727AbiINJBO (ORCPT ); Wed, 14 Sep 2022 05:01:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37952 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230288AbiINJAs (ORCPT ); Wed, 14 Sep 2022 05:00:48 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A52445F8E; Wed, 14 Sep 2022 02:00:38 -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 487A35CD35; Wed, 14 Sep 2022 09:00:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1663146037; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=++TRGvwUmp+i5nL8+2zUUfPddCZzIMndHJUJU3TWquc=; b=0pJVoKCAJ3FBW3e1gyMtWHemmHz7UDLUu0VEFMGTyY8gaY1LTEGZoiWQKG28goN5FloqPb i4JmEYtwjE841exwbCpLmSljMeNbOm/4wnOGVdQSq6yKGqBb6dq3i90rvP1Mp55rIv5CNw CemMlwLK4kon39piQkntcYtMAqdtqLU= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1663146037; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=++TRGvwUmp+i5nL8+2zUUfPddCZzIMndHJUJU3TWquc=; b=W/FlRVx3EDd2iGJRcFy5GRKA4ZOATIqe2iAtwQV9BRa+RvcyfvK7ZIdxemUiG7eJjZO/V6 IA9o7fdI47wKyZDw== 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 3925813494; Wed, 14 Sep 2022 09:00:37 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id o8fzDTWYIWOKHQAAMHmgww (envelope-from ); Wed, 14 Sep 2022 09:00:37 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id C8E99A0680; Wed, 14 Sep 2022 11:00:36 +0200 (CEST) Date: Wed, 14 Sep 2022 11:00:36 +0200 From: Jan Kara To: Yu Kuai Cc: Paolo VALENTE , Jan Kara , cgroups@vger.kernel.org, linux-block , Tejun Heo , Jens Axboe , LKML , yi.zhang@huawei.com, "yukuai (C)" Subject: Re: [PATCH -next v10 3/4] block, bfq: refactor the counting of 'num_groups_with_pending_reqs' Message-ID: <20220914090036.46zsrj2l23ubvvk6@quack3> References: <2f94f241-445f-1beb-c4a8-73f6efce5af2@huaweicloud.com> <55A07102-BE55-4606-9E32-64E884064FB9@unimore.it> <5cb0e5bc-feec-86d6-6f60-3c28ee625efd@huaweicloud.com> <5e0b44b4-46cc-b3c6-1d93-00a0a683eda8@huaweicloud.com> <97534773-484f-5c2c-a371-446cc0680b73@huaweicloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <97534773-484f-5c2c-a371-446cc0680b73@huaweicloud.com> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi guys! On Wed 14-09-22 16:15:26, Yu Kuai wrote: > 在 2022/09/14 15:50, Paolo VALENTE 写道: > > > > > > > Il giorno 14 set 2022, alle ore 03:55, Yu Kuai ha scritto: > > > > > > > > > > > > 在 2022/09/07 9:16, Yu Kuai 写道: > > > > Hi, Paolo! > > > > 在 2022/09/06 17:37, Paolo Valente 写道: > > > > > > > > > > > > > > > > Il giorno 26 ago 2022, alle ore 04:34, Yu Kuai ha scritto: > > > > > > > > > > > > Hi, Paolo! > > > > > > > > > > > > 在 2022/08/25 22:59, Paolo Valente 写道: > > > > > > > > Il giorno 11 ago 2022, alle ore 03:19, Yu Kuai > ha scritto: > > > > > > > > > > > > > > > > Hi, Paolo > > > > > > > > > > > > > > > > 在 2022/08/10 18:49, Paolo Valente 写道: > > > > > > > > > > Il giorno 27 lug 2022, alle ore 14:11, Yu Kuai > ha scritto: > > > > > > > > > > > > > > > > > > > > Hi, Paolo > > > > > > > > > > > > > > > > > > > hi > > > > > > > > > > Are you still interested in this patchset? > > > > > > > > > > > > > > > > > > > Yes. Sorry for replying very late again. > > > > > > > > > Probably the last fix that you suggest is enough, but I'm a little bit > > > > > > > > > concerned that it may be a little hasty. In fact, before this fix, we > > > > > > > > > exchanged several messages, and I didn't seem to be very good at > > > > > > > > > convincing you about the need to keep into account also in-service > > > > > > > > > I/O. So, my question is: are you sure that now you have a > > > > > > > > > > > > > > > > I'm confused here, I'm pretty aware that in-service I/O(as said pending > > > > > > > > requests is the patchset) should be counted, as you suggested in v7, are > > > > > > > > you still thinking that the way in this patchset is problematic? > > > > > > > > > > > > > > > > I'll try to explain again that how to track is bfqq has pending pending > > > > > > > > requests, please let me know if you still think there are some problems: > > > > > > > > > > > > > > > > patch 1 support to track if bfqq has pending requests, it's > > > > > > > > done by setting the flag 'entity->in_groups_with_pending_reqs' when the > > > > > > > > first request is inserted to bfqq, and it's cleared when the last > > > > > > > > request is completed. specifically the flag is set in > > > > > > > > bfq_add_bfqq_busy() when 'bfqq->dispatched' if false, and it's cleared > > > > > > > > both in bfq_completed_request() and bfq_del_bfqq_busy() when > > > > > > > > 'bfqq->diapatched' is false. > > > > > > > > > > > > > > > This general description seems correct to me. Have you already sent a new version of your patchset? > > > > > > > > > > > > It's glad that we finially on the same page here. > > > > > > > > > > > > > > > > Yep. Sorry for my chronicle delay. > > > > Better late than never 😁 > > > > > > > > > > > Please take a look at patch 1, which already impelement the above > > > > > > descriptions, it seems to me there is no need to send a new version > > > > > > for now. If you think there are still some other problems, please let > > > > > > me know. > > > > > > > > > > > > > > > > Patch 1 seems ok to me. I seem to have only one pending comment on this patch (3/4) instead. Let me paste previous stuff here for your convenience: > > > > That sounds good. > > > > > > > > > > > > > > > > > > > - /* > > > > > > > - * Next function is invoked last, because it causes bfqq to be > > > > > > > - * freed if the following holds: bfqq is not in service and > > > > > > > - * has no dispatched request. DO NOT use bfqq after the next > > > > > > > - * function invocation. > > > > > > > - */ > > > > > > I would really love it if you leave this comment. I added it after > > > > > > suffering a lot for a nasty UAF. Of course the first sentence may > > > > > > need to be adjusted if the code that precedes it is to be removed. > > > > > > Same as above, if this patch is applied, this function will be gone. > > > > > > Hi, I'm curious while I'm trying to add the comment, before this > > > patchset, can bfqq be freed when bfq_weights_tree_remove is called? > > > > > > bfq_completed_request > > > bfqq->dispatched-- > > > if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) > > > bfq_weights_tree_remove(bfqd, bfqq); > > > > > > // continue to use bfqq > > > > > > It seems to me this is problematic if so, because bfqq is used after > > > bfq_weights_tree_remove() is called. > > > > > > > It is. Yet, IIRC, I verified that bfqq was not used after that free, > > and I added that comment as a heads-up. What is a scenario (before > > your pending modifications) where this use-after-free happens? > > > > No, it never happens, I just notice it because it'll be weird if I > place the comment where bfq_weights_tree_remove() is called, since bfqq > will still be accessed. > > If the suituation that the comment says is possible, perhaps we should > move bfq_weights_tree_remove() to the last of bfq_completed_request(). > However, it seems that we haven't meet the problem for quite a long > time... I'm bit confused which comment you are speaking about but bfq_completed_request() gets called only from bfq_finish_requeue_request() and the request itself still holds a reference to bfqq. Only later in bfq_finish_requeue_request() when we do: bfqq_request_freed(bfqq); bfq_put_queue(bfqq); bfqq can get freed. Honza -- Jan Kara SUSE Labs, CR