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=-5.8 required=3.0 tests=BAYES_00,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 C4CA4C07E99 for ; Mon, 5 Jul 2021 16:34:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 99AF5613D1 for ; Mon, 5 Jul 2021 16:34:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229743AbhGEQgj (ORCPT ); Mon, 5 Jul 2021 12:36:39 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:55814 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229560AbhGEQgi (ORCPT ); Mon, 5 Jul 2021 12:36:38 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id BEF7D203A4; Mon, 5 Jul 2021 16:34:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1625502840; h=from:from:reply-to: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=rkPXIuH/RB2D0QQyUgwo3tt0LzV1ZF0yIHcY5Q7RSRA=; b=dhQONS9SP70K9gmKDN1/3brZ6Ws7J1+ecCqYz1p2GG0YG03FI4IH6fHwbmokt1r7ya3LId AUAuMzuTQ1/kI9JaHFTNlp8unvQ08SuWzPI4I6hDly31837s4vo/g+/oW2PHbrvdh9MEHq ZmGICP3Tky5YTT10yU+K0fySIxa8VhI= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1625502840; h=from:from:reply-to: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=rkPXIuH/RB2D0QQyUgwo3tt0LzV1ZF0yIHcY5Q7RSRA=; b=GGH+zTrRWKqliCGxDTsieZ7pw98QA3b+Ipk/dEoTlWDBiCIN9d3s6+/5TX9pX0HKT9m8iL Gp8GOJBB2wgUfdCw== Received: from localhost (unknown [10.163.25.122]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 98709A3BA8; Mon, 5 Jul 2021 16:34:00 +0000 (UTC) Date: Mon, 5 Jul 2021 18:34:00 +0200 From: Daniel Wagner To: Ming Lei 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: <20210705162519.qqlklisxcsiopflw@beryllium.lan> References: <20210625101649.49296-1-dwagner@suse.de> <20210625101649.49296-3-dwagner@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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.