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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7EC5BC433E1 for ; Wed, 3 Jun 2020 12:00:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6816520678 for ; Wed, 3 Jun 2020 12:00:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726084AbgFCMAm (ORCPT ); Wed, 3 Jun 2020 08:00:42 -0400 Received: from lhrrgout.huawei.com ([185.176.76.210]:2270 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725833AbgFCMAl (ORCPT ); Wed, 3 Jun 2020 08:00:41 -0400 Received: from lhreml724-chm.china.huawei.com (unknown [172.18.7.106]) by Forcepoint Email with ESMTP id 8ED93C327E73F3D3C7B3; Wed, 3 Jun 2020 13:00:40 +0100 (IST) Received: from [127.0.0.1] (10.47.0.59) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1913.5; Wed, 3 Jun 2020 13:00:39 +0100 Subject: Re: [PATCH 1/1] blk-mq: get ctx in order to handle BLK_MQ_S_INACTIVE in blk_mq_get_tag() To: Dongli Zhang , CC: , , , , , Christoph Hellwig References: <20200602061749.32029-1-dongli.zhang@oracle.com> From: John Garry Message-ID: <2114e1a8-253b-9ad7-0991-afc15df365bd@huawei.com> Date: Wed, 3 Jun 2020 12:59:28 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: <20200602061749.32029-1-dongli.zhang@oracle.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.47.0.59] X-ClientProxiedBy: lhreml735-chm.china.huawei.com (10.201.108.86) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/06/2020 07:17, Dongli Zhang wrote: > When scheduler is set, we hit below page fault when we offline cpu. > > [ 1061.007725] BUG: kernel NULL pointer dereference, address: 0000000000000040 > [ 1061.008710] #PF: supervisor read access in kernel mode > [ 1061.009492] #PF: error_code(0x0000) - not-present page > [ 1061.010241] PGD 0 P4D 0 > [ 1061.010614] Oops: 0000 [#1] SMP PTI > [ 1061.011130] CPU: 0 PID: 122 Comm: kworker/0:1H Not tainted 5.7.0-rc7+ #2' > ... ... > [ 1061.013760] Workqueue: kblockd blk_mq_run_work_fn > [ 1061.014446] RIP: 0010:blk_mq_put_tag+0xf/0x30 > ... ... > [ 1061.017726] RSP: 0018:ffffa5c18037fc70 EFLAGS: 00010287 > [ 1061.018475] RAX: 0000000000000000 RBX: ffffa5c18037fcf0 RCX: 0000000000000004 > [ 1061.019507] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff911535dc1180 > ... ... > [ 1061.028454] Call Trace: > [ 1061.029307] blk_mq_get_tag+0x26e/0x280 > [ 1061.029866] ? wait_woken+0x80/0x80 > [ 1061.030378] blk_mq_get_driver_tag+0x99/0x110 > [ 1061.031009] blk_mq_dispatch_rq_list+0x107/0x5e0 > [ 1061.031672] ? elv_rb_del+0x1a/0x30 > [ 1061.032178] blk_mq_do_dispatch_sched+0xe2/0x130 > [ 1061.032844] __blk_mq_sched_dispatch_requests+0xcc/0x150 > [ 1061.033638] blk_mq_sched_dispatch_requests+0x2b/0x50 > [ 1061.034239] __blk_mq_run_hw_queue+0x75/0x110 > [ 1061.034867] process_one_work+0x15c/0x370 > [ 1061.035450] worker_thread+0x44/0x3d0 > [ 1061.035980] kthread+0xf3/0x130 > [ 1061.036440] ? max_active_store+0x80/0x80 > [ 1061.037018] ? kthread_bind+0x10/0x10 > [ 1061.037554] ret_from_fork+0x35/0x40 > [ 1061.038073] Modules linked in: > [ 1061.038543] CR2: 0000000000000040 > [ 1061.038962] ---[ end trace d20e1df7d028e69f ]--- > > This is because blk_mq_get_driver_tag() would be used to allocate tag once > scheduler (e.g., mq-deadline) is set. I tried mq-deadline and I did not see this. Anyway else special or specific about your test? However, I see other issues for that (setting the scheduler), that being scsi timeouts when I start running IO and hotplugging CPUs. I should have tested the scheduler != none previously for "blk-mq: improvement CPU hotplug (simplified version) " series ... I'll check Ming's patch "[PATCH] blk-mq: don't fail driver tag allocation because of inactive hctx" for that. Thanks, John However, in order to handle > BLK_MQ_S_INACTIVE in blk_mq_get_tag(), we need to set data->ctx for > blk_mq_put_tag(). > > Fixes: bf0beec0607db3c6 ("blk-mq: drain I/O when all CPUs in a hctx are offline") > Signed-off-by: Dongli Zhang > --- > This is based on for-next because currently the pull request for v5.8 is > not picked by mainline. > > block/blk-mq.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 9a36ac1c1fa1..8bf6c06a86c1 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1056,6 +1056,7 @@ bool blk_mq_get_driver_tag(struct request *rq) > { > struct blk_mq_alloc_data data = { > .q = rq->q, > + .ctx = rq->mq_ctx, > .hctx = rq->mq_hctx, > .flags = BLK_MQ_REQ_NOWAIT, > .cmd_flags = rq->cmd_flags, >