From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F03921940B3; Mon, 25 Nov 2024 10:50:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732531844; cv=none; b=jCScvSjiwHwdd42OriygoVg//hzx+MEbBfSTYe9up3W6LOj27Mb52Flf2GOHzRpa0LFCd5vLpmQAd26fnhgfaIeCxogdpk7o4c0/LFE/LgtsA01uuX0lDgj2txHu+jqcJNM0CAwoEE2eY9aLtIb7HAKzkc6bY9roVKevEds8lfQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732531844; c=relaxed/simple; bh=9hXOVBNdgVCWJqpNWpCcCp/Lejcixifw+eGIIr0WdSA=; h=Subject:To:Cc:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=n7jBh8BM/34jO6ZC24NXeC2b2cebAxa0sesGb2pUZT7BLydH1PPVkB+X69c95LOm0xdBeNIEtPtjw5GA6C+RIlUs2/v1MyZ1WxR5EhmCqkRTczY2wRdoFtIaIGlq3se0R2lDYmXCYLmKQxuWRmduF80/b71lXOxzao3xmEcF9q4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.163.216]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTP id 4XxjCT0KHrz4f3jXK; Mon, 25 Nov 2024 18:50:13 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id B6D8F1A0197; Mon, 25 Nov 2024 18:50:31 +0800 (CST) Received: from [10.174.176.73] (unknown [10.174.176.73]) by APP4 (Coremail) with SMTP id gCh0CgCngYV1VkRnOnwnCw--.39352S3; Mon, 25 Nov 2024 18:50:31 +0800 (CST) Subject: Re: [PATCH] block: iocost: ensure hweight_inuse is at least 1 To: =?UTF-8?B?5oi05Z2k5rW3IFRvbnkgRGFp?= , Yu Kuai , "tj@kernel.org" , "josef@toxicpanda.com" , "axboe@kernel.dk" Cc: "cgroups@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "yukuai (C)" References: <3B8BC663-3B34-454D-AE79-4FCE50001D6E@didiglobal.com> From: Yu Kuai Message-ID: <3e69ac2d-aa3b-2065-2bb6-d3888fddfe5a@huaweicloud.com> Date: Mon, 25 Nov 2024 18:50:29 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <3B8BC663-3B34-454D-AE79-4FCE50001D6E@didiglobal.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgCngYV1VkRnOnwnCw--.39352S3 X-Coremail-Antispam: 1UD129KBjvJXoW7KF4rKFy7tr18Jr1DCw4kJFb_yoW5JryDpr WrW3WYyFZrGF4I93WrKr129wn0vws3WF4xKrn3Z3yxCr48Gr9Ikr1xKF4DW34rXrsaqr4I vw17KFyrG3y7Cr7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvK14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvEwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lc7I2V7IY0VAS07AlzVAY IcxG8wCY1x0262kKe7AKxVWUtVW8ZwCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7xkEbV WUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF 67kF1VAFwI0_Jw0_GFylIxkGc2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42 IY6xIIjxv20xvEc7CjxVAFwI0_Jr0_Gr1lIxAIcVCF04k26cxKx2IYs7xG6r1j6r1xMIIF 0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxh VjvjDU0xZFpf9x0JUd-B_UUUUU= X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ Hi 在 2024/11/24 21:44, 戴坤海 Tony Dai 写道: > In fact, we did encounter such a special situation where the kernel printed out `iocg: invalid donation weights in /a/b/c: active=1 donating=1 after=0`, and then it immediately panic. I analyzed the code but could not figure out how this happened; it might be a concurrency issue or some other hidden bug. Do you have a reporducer for this? I'd like to take a look at the WARN first. Thanks, Kuai > > Our kernel is not the latest, but it includes the patch edaa26334c117a584add6053f48d63a988d25a6e (iocost: Fix divide-by-zero on donation from low hweight cgroup). > > 在 2024/11/22 16:16，“Yu Kuai”> 写入: > > > Hi, > > > 在 2024/11/22 15:26, Kunhai Dai 写道: >> The hweight_inuse calculation in transfer_surpluses() could potentially >> result in a value of 0, which would lead to division by zero errors in >> subsequent calculations that use this value as a divisor. >> >> Signed-off-by: Kunhai Dai > >> --- >> block/blk-iocost.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/block/blk-iocost.c b/block/blk-iocost.c >> index 384aa15e8260..65cdb55d30cc 100644 >> --- a/block/blk-iocost.c >> +++ b/block/blk-iocost.c >> @@ -1999,9 +1999,10 @@ static void transfer_surpluses(struct list_head *surpluses, struct ioc_now *now) >> parent = iocg->ancestors[iocg->level - 1]; >> >> /* b' = gamma * b_f + b_t' */ >> - iocg->hweight_inuse = DIV64_U64_ROUND_UP( >> - (u64)gamma * (iocg->hweight_active - iocg->hweight_donating), >> - WEIGHT_ONE) + iocg->hweight_after_donation; >> + iocg->hweight_inuse = max_t(u64, 1, >> + DIV64_U64_ROUND_UP( >> + (u64)gamma * (iocg->hweight_active - iocg->hweight_donating), >> + WEIGHT_ONE) + iocg->hweight_after_donation); > > > I'm confused, how could DIV64_U64_Round_UP() end up less than 1? > > > #define DIV64_U64_ROUND_UP(ll, d) \ > ({ u64 _tmp = (d); div64_u64((ll) + _tmp - 1, _tmp); }) > > > AFAIK, the only case that could happen is that > iocg->hweight_active - iocg->hweight_donating is 0, then I don't > get it now how cound active iocg donate all the hweight, if this > really happend perhaps the better solution is to avoid such case. > > > Thanks, > Kuai > > >> >> /* w' = s' * b' / b'_p */ >> inuse = DIV64_U64_ROUND_UP( >> > > > > >