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=-7.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 E6C24C07E96 for ; Tue, 6 Jul 2021 07:29:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B8F166198D for ; Tue, 6 Jul 2021 07:29:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230232AbhGFHcE (ORCPT ); Tue, 6 Jul 2021 03:32:04 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:53704 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230203AbhGFHcD (ORCPT ); Tue, 6 Jul 2021 03:32:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1625556565; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=nw0P33cYxqMaEBdimkgujl5GLUpaC+SctslNj38QzXU=; b=fLF8gNYMcFRT67r4SF1S3XCeEnwp9ryoUzwfTJBqdcKvYFLtZKpaxjzw1ifTUtPnXwPY2w Bz2BKuTkgv/V8kvo22sKHeizI0RC8X/8+9ak1p+dLOiPbj7i/iiL/fxmzh0FtKs8MwrNse a/x/6fC/RuKqI0jZJIWfq/Y3Ve5J42Q= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-567-qsHgqo21NZyc2_bgpJSftQ-1; Tue, 06 Jul 2021 03:29:24 -0400 X-MC-Unique: qsHgqo21NZyc2_bgpJSftQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 59F6A1932480; Tue, 6 Jul 2021 07:29:22 +0000 (UTC) Received: from T590 (ovpn-12-27.pek2.redhat.com [10.72.12.27]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 671C55D6A1; Tue, 6 Jul 2021 07:29:16 +0000 (UTC) Date: Tue, 6 Jul 2021 15:29:11 +0800 From: Ming Lei To: Daniel Wagner Cc: linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, James Smart , Keith Busch , Jens Axboe , Sagi Grimberg Subject: Re: [PATCH 2/2] nvme-fc: Wait with a timeout for queue to freeze Message-ID: References: <20210625101649.49296-1-dwagner@suse.de> <20210625101649.49296-3-dwagner@suse.de> <20210705162519.qqlklisxcsiopflw@beryllium.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210705162519.qqlklisxcsiopflw@beryllium.lan> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 05, 2021 at 06:34:00PM +0200, Daniel Wagner wrote: > On Tue, Jun 29, 2021 at 09:39:30AM +0800, Ming Lei wrote: > > Can you investigate a bit on why there is the hang? FC shouldn't use > > managed IRQ, so the interrupt won't be shutdown. > > So far, I was not able to figure out why this hangs. In my test setup I > don't have to do any I/O, I just toggle the remote port. > > grep busy /sys/kernel/debug/block/*/hctx*/tags | grep -v busy=0 > > and this seems to confirm, no I/O in flight. What is the output of the following command after the hang is triggered? (cd /sys/kernel/debug/block/nvme0n1 && find . -type f -exec grep -aH . {} \;) Suppose the hang disk is nvme0n1. > > So I started to look at the q_usage_counter. The obvious observational > is that counter is not 0. The least bit is set, thus we are in atomic > mode. > > (gdb) p/x *((struct request_queue*)0xffff8ac992fbef20)->q_usage_counter->data > $10 = { > count = { > counter = 0x8000000000000001 > }, > release = 0xffffffffa02e78b0, > confirm_switch = 0x0, > force_atomic = 0x0, > allow_reinit = 0x1, > rcu = { > next = 0x0, > func = 0x0 > }, > ref = 0xffff8ac992fbef30 > } > > I am a bit confused about the percpu-refcount API. My naive > interpretation is that when we are in atomic mode percpu_ref_is_zero() > can't be used. But this seems rather strange. I must miss something. No, percpu_ref_is_zero() is fine to be called in atomic mode. Thanks, Ming