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=-6.1 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 78D88C433E2 for ; Sat, 29 Aug 2020 07:25:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 38101207BB for ; Sat, 29 Aug 2020 07:25:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726170AbgH2HZN (ORCPT ); Sat, 29 Aug 2020 03:25:13 -0400 Received: from comms.puri.sm ([159.203.221.185]:53946 "EHLO comms.puri.sm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726083AbgH2HZG (ORCPT ); Sat, 29 Aug 2020 03:25:06 -0400 Received: from localhost (localhost [127.0.0.1]) by comms.puri.sm (Postfix) with ESMTP id 57DC3E035E; Sat, 29 Aug 2020 00:24:35 -0700 (PDT) Received: from comms.puri.sm ([127.0.0.1]) by localhost (comms.puri.sm [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id IKjiLLbPQD1r; Sat, 29 Aug 2020 00:24:34 -0700 (PDT) Subject: Re: [PATCH] block: Fix bug in runtime-resume handling To: Alan Stern Cc: Bart Van Assche , Can Guo , linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, kernel@puri.sm References: <20200809152643.GA277165@rowland.harvard.edu> <60150284-be13-d373-5448-651b72a7c4c9@puri.sm> <20200810141343.GA299045@rowland.harvard.edu> <6f0c530f-4309-ab1e-393b-83bf8367f59e@puri.sm> <20200823145733.GC303967@rowland.harvard.edu> <3e5a465e-8fe0-b379-a80e-23e2f588c71a@acm.org> <20200824201343.GA344424@rowland.harvard.edu> <5152a510-bebf-bf33-f6b3-4549e50386ab@puri.sm> <4c636f2d-af7f-bbde-a864-dbeb67c590ec@puri.sm> <20200827202952.GA449067@rowland.harvard.edu> From: Martin Kepplinger Autocrypt: addr=martin.kepplinger@puri.sm; keydata= mQINBFULfZABEADRxJqDOYAHfrp1w8Egcv88qoru37k1x0Ugy8S6qYtKLAAt7boZW+q5gPv3 Sj2KjfkWA7gotXpASN21OIfE/puKGwhDLAySY1DGNMQ0gIVakUO0ji5GJPjeB9JlmN5hbA87 Si9k3yKQQfv7Cf9Lr1iZaV4A4yjLP/JQMImaCVdC5KyqJ98Luwci1GbsLIGX3EEjfg1+MceO dnJTKZpBAKd1J7S2Ib3dRwvALdiD7zqMGqkw5xrtwasatS7pc6o/BFgA9GxbeIzKmvW/hc3Q amS/sB12BojyzdUJ3TnIoAqvwKTGcv5VYo2Z+3FV+/MJVXPo8cj2vmfxQx1WG4n6X0pK4X8A BkCKw2N/evMZblNqAzzGVtoJvqQYkzQ20Fm+d3wFl6lS1db4MB+kU13G8kEIE22Q3i6kx4NA N49FLlPeDabGfJUyDaZp5pmKdcd7/FIGH/HjShjx7g+LKSwWNMkDygr4WARAP4h8zYDZuNqe ofPvMLqJxHeexBPIGF/+OwMyTvM7otP5ODuFmq6OqjNPf1irJmkiFv3yEa+Ip0vZzwl4XvrZ U0IKjSy2rbRLg22NsJT0XVZJbutIXYSvIHGqSxzzfiOOLnRjR++fbeEoVlRJ4NZHDKCh3pJv LNd+j03jXr4Rm058YLgO7164yr7FhMZniBJw6z648rk8/8gGPQARAQABtC1NYXJ0aW4gS2Vw cGxpbmdlciA8bWFydGluLmtlcHBsaW5nZXJAcHVyaS5zbT6JAk4EEwEIADgWIQTyCCuID55C OTRobj9QA5jfWrOH0wUCXPSlkwIbAwULCQgHAgYVCAkKCwIEFgIDAQIeAQIXgAAKCRBQA5jf 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Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 27.08.20 22:29, Alan Stern wrote: > On Thu, Aug 27, 2020 at 07:42:43PM +0200, Martin Kepplinger wrote: >> On 26.08.20 09:48, Martin Kepplinger wrote: >>> On 24.08.20 22:13, Alan Stern wrote: > >>>> Martin: >>>> >>>> (I forgot to ask this question several weeks ago, while you were running >>>> your tests. Better ask it now before I forget again...) >>>> >>>> I suspect the old runtime-PM code in the block layer would have worked >>>> okay in your SD cardreader test if the BLK_MQ_REQ_PREEMPT flag had not >>>> been set. Do you know why the flag was set, or what line of code caused >>>> it to be set? >>> >>> Correct. if not set, I could handle all I need in the scsi error path. >> >> this thread becomes a bit confusing. I thought about REQ_FAILFAST_DEV >> but you're talking about something different. >> >> the only place I see BLK_MQ_REQ_PREEMPT getting passed on is in >> __scsi_execute() which is the case when mounting/unmounting. At least >> that about the only place I can find. > > Ah yes, I see what you mean. > >> I remember *only* your block pm fix would let me mount/unmount, but not >> use files yet (REQ_FAILFAST_DEV and so on). >> >> When I revert your fix and remove BLK_MQ_REQ_PREEMPT from being passed >> on to blk_get_request() in __scsi_execute(), that line gets executed >> exactly once during startup and I'm missing the /dev/sda device from the >> cardreader then. >> >> Is this what you're asking? > > Not quite sure, but it doesn't matter. Removing BLK_MQ_REQ_PREEMPT in > __scsi_execute() is probably not a safe thing to do. > > Instead, look at sd_resume(). That routine calls __scsi_execute() > indirectly through sd_start_stop_device(), and the only reason it does > this is because the sdkp->device->manage_start_stop flag is set. You > ought to be able to clear this flag in sysfs, by writing to > /sys/block/sda/device/scsi_disk/*/manage_start_stop. If you do this > before allowing the card reader to go into runtime suspend, does it then > resume okay? manage_start_stop in sysfs is 0 here. > > (Yes, I know you still won't be able to read it because of the FAILFAST > flag. I just want to know if the runtime resume actually takes place.) > > Alan Stern >