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=-3.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS 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 570E0C169C4 for ; Tue, 12 Feb 2019 02:13:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E36721B18 for ; Tue, 12 Feb 2019 02:13:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=hansenpartnership.com header.i=@hansenpartnership.com header.b="unqG1yui" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728107AbfBLCNW (ORCPT ); Mon, 11 Feb 2019 21:13:22 -0500 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:55792 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726892AbfBLCNV (ORCPT ); Mon, 11 Feb 2019 21:13:21 -0500 Received: from localhost (localhost [127.0.0.1]) by bedivere.hansenpartnership.com (Postfix) with ESMTP id 941058EE235; Mon, 11 Feb 2019 18:13:20 -0800 (PST) Received: from bedivere.hansenpartnership.com ([127.0.0.1]) by localhost (bedivere.hansenpartnership.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id UrtSqye5YGDN; Mon, 11 Feb 2019 18:13:20 -0800 (PST) Received: from [153.66.254.194] (unknown [50.35.68.20]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by bedivere.hansenpartnership.com (Postfix) with ESMTPSA id E4A1E8EE121; Mon, 11 Feb 2019 18:13:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=hansenpartnership.com; s=20151216; t=1549937600; bh=KBhzEtkPpbaseZywwnvd0oXt0Bsk3bbNgDswOxjTeSo=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=unqG1yuiNG6vL0WKdiW56GJaxZs1/TNIith53lbmY+rfR4kx59YwFNR0AHoCwP0ET seu0j6rvvMD1Sd6s0LX9rYTVTusYSDlwGSFXqI7UMwXZ+q97ukPQgBk1ZQhjyplgjG EHZbae58pZfgmQQPU0cx94jYqBfq4s3st284pgBU= Message-ID: <1549937598.2857.8.camel@HansenPartnership.com> Subject: Re: [5.0-rc5 regression] "scsi: kill off the legacy IO path" causes 5 minute delay during boot on Sun Blade 2500 From: James Bottomley To: Jens Axboe , Mikael Pettersson Cc: Linux SPARC Kernel Mailing List , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-scsi Date: Mon, 11 Feb 2019 18:13:18 -0800 In-Reply-To: References: <1549736341.2971.7.camel@HansenPartnership.com> <1549813472.4142.3.camel@HansenPartnership.com> <3380ed8e-ae02-96f2-142b-7cce09459df8@kernel.dk> <1549815924.4142.8.camel@HansenPartnership.com> <0e6e5d67-d305-dd00-2e42-e2299166c8b2@kernel.dk> <1549898730.2831.6.camel@HansenPartnership.com> <44bb4374-0b7c-733b-a53e-92d2f03f2f49@kernel.dk> <1549899773.2831.12.camel@HansenPartnership.com> <1a00da0e-cb8e-30ea-8d17-120f97242b2f@kernel.dk> <1549902521.2831.23.camel@HansenPartnership.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2019-02-11 at 09:31 -0700, Jens Axboe wrote: > On 2/11/19 9:28 AM, James Bottomley wrote: > > On Mon, 2019-02-11 at 08:46 -0700, Jens Axboe wrote: > > > On 2/11/19 8:42 AM, James Bottomley wrote: > > > > On Mon, 2019-02-11 at 08:28 -0700, Jens Axboe wrote: > > > > > On 2/11/19 8:25 AM, James Bottomley wrote: > > > > > > On Sun, 2019-02-10 at 09:35 -0700, Jens Axboe wrote: > > > > > > > On 2/10/19 9:25 AM, James Bottomley wrote: > > > > [...] > > > > > > > > That check wasn't changed by the code removal. > > > > > > > > > > > > > > As I said above, for sd. This isn't true for non-disks. > > > > > > > > > > > > Yes, but the behaviour above doesn't change across a switch > > > > > > to MQ, so I don't quite understand how it bisects back to > > > > > > that change. If we're not gathering entropy for the device > > > > > > now, we wouldn't have been before the switch, so the > > > > > > entropy characteristics shouldn't have changed. > > > > > > > > > > But it does, as I also wrote in that first email. The legacy > > > > > queue flags had QUEUE_FLAG_ADD_RANDOM set by default, the MQ > > > > > ones do not. Hence any non-sd device would previously ALWAYS > > > > > have ADD_RANDOM set, now none of them do. Also see the patch > > > > > I sent. > > > > > > > > So your theory is that the disk in question never gets to the > > > > rotational check? because the check will clear the flag if > > > > it's non-rotational and set it if it's not, so the default > > > > state of the flag shouldn't matter. > > > > > > No, my point is about non-disks, devices that aren't driven by > > > sd. The behavior for sd hasn't changed, as it sets/clears it > > > unconditionally. > > > > I agree, but I don't think any of them were significant entropy > > contributors before: things like nvme have always been outside of > > this and sr and st don't really contribute much to the seek load > > during boot because they're probed but not used by the boot > > sequence, so I can't see how they would cause this behaviour. I > > suppose it could be target probing, but even that seems unlikely > > because it should be dwarfed by the number of root disk reads > > during boot. > > > > For the rng to take an additional 5 minutes to initialize, we must > > have lost a significant entropy source somewhere. > > I agree it's not a significant amount of entropy, but even just one > bit could mean a long stall if that put us over the edge of just not > having enough for whatever is blocking on /dev/random. Mikael's boot > did have a CDROM, it's not impossible that the handful of commands we > end up doing to that device would have contributed enough entropy to > get the boot done without stalling for minutes. > > One way to know for sure, and that's if Mikael tests the patch. I think I've got the root cause. I have one system in my test bed exhibiting this behaviour. It turns out the disk in it has no characteristics VPD page. The 0xB1 VPD was a SBC-3 addition, so that's not surprising. However, the characteristics check bails before setting the flags, so it takes the default flag which has flipped. We can either fix this by setting the QUEUE_FLAG_ADD_RANDOM if there's no 0xB1 page or by setting the default as Jens proposed. James --- diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index d0a980915801..1f3a1474042e 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -2961,6 +2961,10 @@ static void sd_read_block_characteristics(struct scsi_disk *sdkp) buffer = kmalloc(vpd_len, GFP_KERNEL); + /* set to rotational in case no device characteristic page exists */ + blk_queue_flag_clear(QUEUE_FLAG_NONROT, q); + blk_queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q); + if (!buffer || /* Block Device Characteristics VPD */ scsi_get_vpd_page(sdkp->device, 0xb1, buffer, vpd_len)) @@ -2971,9 +2975,6 @@ static void sd_read_block_characteristics(struct scsi_disk *sdkp) if (rot == 1) { blk_queue_flag_set(QUEUE_FLAG_NONROT, q); blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, q); - } else { - blk_queue_flag_clear(QUEUE_FLAG_NONROT, q); - blk_queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q); } if (sdkp->device->type == TYPE_ZBC) {