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 D1F04C43217 for ; Thu, 13 Oct 2022 14:07:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230169AbiJMOHF (ORCPT ); Thu, 13 Oct 2022 10:07:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43224 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229982AbiJMOHB (ORCPT ); Thu, 13 Oct 2022 10:07:01 -0400 Received: from dggsgout11.his.huawei.com (dggsgout11.his.huawei.com [45.249.212.51]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C82D65E308; Thu, 13 Oct 2022 07:06:49 -0700 (PDT) Received: from mail02.huawei.com (unknown [172.30.67.153]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4MpB7s11znzKFPn; Thu, 13 Oct 2022 22:03:37 +0800 (CST) Received: from [10.174.176.73] (unknown [10.174.176.73]) by APP4 (Coremail) with SMTP id gCh0CgCHiMpBG0hjshrZAA--.47785S3; Thu, 13 Oct 2022 22:05:54 +0800 (CST) Subject: Re: [PATCH] blk-mq: put the reference of the io scheduler module after switching back To: Jinlong Chen , yukuai1@huaweicloud.com Cc: axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, "yukuai (C)" References: From: Yu Kuai Message-ID: Date: Thu, 13 Oct 2022 22:05:53 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID: gCh0CgCHiMpBG0hjshrZAA--.47785S3 X-Coremail-Antispam: 1UD129KBjvJXoW7CF1UCw1rWrWkCrWrtr1rCrg_yoW8GFWkpF W8GayYkw4ktr40g3y7Kw47Ja40vrZ5Kr1Ygr1fAa4xXrn5W393Zr1xJa1a9FW5A34vyw1U W34xZFWkZ3s8JrJanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkK14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26F1j6w1UM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26F4j 6r4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x0267AKxVW0oV Cq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0 I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r 4UM4x0Y48IcVAKI48JM4x0x7Aq67IIx4CEVc8vx2IErcIFxwCYjI0SjxkI62AI1cAE67vI Y487MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI 0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUAVWUtwCIc40Y 0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxV WUJVW8JwCI42IY6xAIw20EY4v20xvaj40_Wr1j6rW3Jr1lIxAIcVC2z280aVAFwI0_Jr0_ Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7VUbXdbU UUUUU== X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ÔÚ 2022/10/13 21:47, Jinlong Chen дµÀ: > Hi, Yu Kuai! > >> >> I'm confused here, cause I do think this patch make sense. >> >> blk_mq_update_nr_hw_queues >> // for each queue using the tagset >> blk_mq_freeze_queue >> // if current elevator is not none, swith to none >> blk_mq_elv_switch_none >> // elevator need to be switched back, got a reference to >> // prevent module to be removed. >> __module_get >> elevator_switch(q, NULL); >> >> // switch back from none elevator >> blk_mq_elv_switch_back >> -> should release the module reference here >> blk_mq_unfreeze_queue >> > > We need to release the reference only if blk_mq_elv_switch_back got its own > reference. However, blk_mq_elv_switch_back (precisely elevator_switch_mq) > does not increase the reference of the module it is switching to. > Hence, the reference got in blk_mq_elv_switch_none does not need to be released, > or we'll have to re-increase the reference count manually.' But I don't see elevator_switch() release the referenct of the module it is switching from. It's still not balance to me. Thanks, Kuai > >> >> By the way, I do not test yet, but I think problem can be reporduced: >> >> >> 1. modprobe bfq >> 2. switch elevator to bfq >> 3. trigger blk_mq_update_nr_hw_queues >> 4. switch elevator to none >> 5. rmmod bfq will fail >> > > I tried to reproduce the problem but failed, so I found my mistake. > > Sincerely, > Jinlong Chen > . >