From patchwork Fri Sep 11 22:40:49 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tejun Heo X-Patchwork-Id: 11771583 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D7FB5746 for ; Fri, 11 Sep 2020 22:40:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B78A120770 for ; Fri, 11 Sep 2020 22:40:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599864054; bh=0WnzoqXCclTHhHqFfB6PYCzR6uLt3J7rZwT7EQXkKCw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ZsS397pr5aSUfVMkw7bleSaFemp4Ek8zjgEt+nPZZ6PR4aB8gbsQ5ExPq123+OXKX 4poAoInHZsEXyrexTTp8hg6kx3Yv2+bHIJwFMdNaB5nnpfrw6TUXAa4JiVrO+fZRvi rz3cY48345E5+JQg7oLOWnA9kj12F5fcz1DGbLKk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725873AbgIKWkx (ORCPT ); Fri, 11 Sep 2020 18:40:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44998 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725849AbgIKWkw (ORCPT ); Fri, 11 Sep 2020 18:40:52 -0400 Received: from mail-qk1-x741.google.com (mail-qk1-x741.google.com [IPv6:2607:f8b0:4864:20::741]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B3DAC061573; Fri, 11 Sep 2020 15:40:52 -0700 (PDT) Received: by mail-qk1-x741.google.com with SMTP id q63so10696093qkf.3; Fri, 11 Sep 2020 15:40:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=YYtbWxsMj/6n0uZf9WI97Rz4VWxjIwP6xqNBdneeUNo=; b=JkeVh8VK3P/IsY0yYuXRdbFDfSKwWuZBsdVeYQRNJXfK2KGyYQA/AQG1w6u3J0hR27 xeKsvGfP60teeylfKsR7sGVXFMV23UrkcYS7IDmwba1mQ6wUDlymmXWC2YHbSd29ru18 pt2KX5E/s3IOIPopfD1+EeR9VSvm3ykan7xzxtVrzfWo4ez/vOxR+5JrJjTOwyjKrpFu TuMTwzTuMnCHWaDumPkGYbWJTCWoxq4zR3eSIPh7oON1BRWWNFipreIaAwRz8hYzfHqT 1o5fPvv/NulyfvabHbVdfiQCigpSGk1nVtsUJ2oyfjGmIk7eh233XREeAOk/JxjqdGzp 66JQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=YYtbWxsMj/6n0uZf9WI97Rz4VWxjIwP6xqNBdneeUNo=; b=Z+j1neCA+DIyHAVJooW8hbEFVzaoyF6pPlF3Q7SJAXBl5EuAEUzNro/cHXNwKgZtp2 5HfIB7HfJzgDmPbsdvcM8vMg5TfO2nIxCG9E8jwhMYFlpnpdCT65zoIs1vlcmUhPUgiQ yhJn9E789zcob3AecRt43nn7v01W47oUzBGpVLN3ycsfbSusT+8rrqslCO+BUsxNp7sw JbfUi5oe2rjAHOqJzV2L5zSyJ+cU+zQvfUkp863A/FexSB8QpsRcGsk/CEDoWQ0hH0C9 /GNRr+M86Tr7+CJtS1eDf6nRS8fQijZgWMz/85ytIc81lFq+usl6vZx9boKkJ1IuNaoA QafQ== X-Gm-Message-State: AOAM533K0jI0eXmGgFQJ8YXZF7Hg6asyGiVMGjlrl+gLXmMMKQDaL9Bz gDtfa/DquL6bgx7hbcXnzdc= X-Google-Smtp-Source: ABdhPJzYGdYMQAwnuAGDo9b4JV7knr1wG0BIH42y4L824JuZkGPlSDZvBU9CfgyDOTI4FYI1TP5zbA== X-Received: by 2002:a37:5684:: with SMTP id k126mr3444195qkb.43.1599864051399; Fri, 11 Sep 2020 15:40:51 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::1:95ac]) by smtp.gmail.com with ESMTPSA id b43sm4570299qtk.84.2020.09.11.15.40.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Sep 2020 15:40:50 -0700 (PDT) Date: Fri, 11 Sep 2020 18:40:49 -0400 From: Tejun Heo To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, cgroups@vger.kernel.org Subject: [PATCH v2 block/for-next] blk-iocost: fix divide-by-zero in transfer_surpluses() Message-ID: <20200911224049.GA865564@mtj.thefacebook.com> References: <20200911170746.GG4295@mtj.thefacebook.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Conceptually, root_iocg->hweight_donating must be less than WEIGHT_ONE but all hweight calculations round up and thus it may end up >= WEIGHT_ONE triggering divide-by-zero and other issues. Bound the value to avoid surprises. Signed-off-by: Tejun Heo Fixes: e08d02aa5fc9 ("blk-iocost: implement Andy's method for donation weight updates") Signed-off-by: Tejun Heo --- Jens, I was flipping between doing max_t(, 1) over the whole divider and doing min_t(, WEIGHT_ONE - 1) for hweight_donating. I thought that I as testing after the last change but it obviously wasn't and the previous patch doesn't compile due to missing type argument. Can you please apply this patch instead? I can send an incremental patch if that'd be better. My apologies. Thanks. block/blk-iocost.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/block/blk-iocost.c b/block/blk-iocost.c index fc897bb142bcd..6e29b4dcf3566 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -1881,15 +1881,21 @@ static void transfer_surpluses(struct list_head *surpluses, struct ioc_now *now) /* * Calculate the global donation rate (gamma) - the rate to adjust - * non-donating budgets by. No need to use 64bit multiplication here as - * the first operand is guaranteed to be smaller than WEIGHT_ONE - * (1<<16). + * non-donating budgets by. + * + * No need to use 64bit multiplication here as the first operand is + * guaranteed to be smaller than WEIGHT_ONE (1<<16). + * + * We know that there are beneficiary nodes and the sum of the donating + * hweights can't be whole; however, due to the round-ups during hweight + * calculations, root_iocg->hweight_donating might still end up equal to + * or greater than whole. Limit the range when calculating the divider. * * gamma = (1 - t_r') / (1 - t_r) */ gamma = DIV_ROUND_UP( (WEIGHT_ONE - root_iocg->hweight_after_donation) * WEIGHT_ONE, - WEIGHT_ONE - root_iocg->hweight_donating); + WEIGHT_ONE - min_t(u32, root_iocg->hweight_donating, WEIGHT_ONE - 1)); /* * Calculate adjusted hwi, child_adjusted_sum and inuse for the inner