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=-5.5 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 5D119C433E0 for ; Tue, 11 Aug 2020 07:56:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3F558206B5 for ; Tue, 11 Aug 2020 07:56:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728094AbgHKH4i (ORCPT ); Tue, 11 Aug 2020 03:56:38 -0400 Received: from comms.puri.sm ([159.203.221.185]:37402 "EHLO comms.puri.sm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728060AbgHKH4h (ORCPT ); Tue, 11 Aug 2020 03:56:37 -0400 Received: from localhost (localhost [127.0.0.1]) by comms.puri.sm (Postfix) with ESMTP id 68123E0148; Tue, 11 Aug 2020 00:56:06 -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 J_BogVAAn9AZ; Tue, 11 Aug 2020 00:56:05 -0700 (PDT) Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release To: Alan Stern Cc: James Bottomley , Bart Van Assche , Can Guo , martin.petersen@oracle.com, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, kernel@puri.sm References: <20200730151030.GB6332@rowland.harvard.edu> <9b80ca7c-39f8-e52d-2535-8b0baf93c7d1@puri.sm> <425990b3-4b0b-4dcf-24dc-4e7e60d5869d@puri.sm> <20200807143002.GE226516@rowland.harvard.edu> <20200808150542.GB256751@rowland.harvard.edu> <20200809152643.GA277165@rowland.harvard.edu> <60150284-be13-d373-5448-651b72a7c4c9@puri.sm> <20200810141343.GA299045@rowland.harvard.edu> From: Martin Kepplinger Autocrypt: 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10.08.20 16:13, Alan Stern wrote: > On Mon, Aug 10, 2020 at 02:03:17PM +0200, Martin Kepplinger wrote: >> On 09.08.20 17:26, Alan Stern wrote: >>> This is a somewhat fragile approach. You don't know for certain that >>> scsi_noretry_cmd will be called. Also, scsi_noretry_cmd can be called >>> from other places. >>> >>> It would be better to clear the expecting_media_change flag just before >>> returning from scsi_decide_disposition. That way its use is localized >>> to one routine, not spread out between two. >>> >>> Alan Stern >>> >> >> Hi Alan, >> >> maybe you're right. I initially just thought that I'd allow for specific >> error codes in scsi_noretry_cmd() to return non-NULL (BUS_BUSY, PARITY, >> ERROR) despite having the flag set. >> >> The below version works equally fine for me but I'm not sure if it's >> actually more safe. >> >> James, when exposing a new writable sysfs option like >> "suspend_no_media_change"(?) that drivers can check before setting the >> new "expecting_media_change" flag (during resume), would this addition >> make sense to you? >> >> thanks, >> >> martin >> >> >> >> --- a/drivers/scsi/scsi_error.c >> +++ b/drivers/scsi/scsi_error.c >> @@ -565,6 +565,18 @@ int scsi_check_sense(struct scsi_cmnd *scmd) >> return NEEDS_RETRY; >> } >> } >> + if (scmd->device->expecting_media_change) { >> + if (sshdr.asc == 0x28 && sshdr.ascq == 0x00) { >> + /* >> + * clear the expecting_media_change in >> + * scsi_decide_disposition() because we >> + * need to catch possible "fail fast" overrides >> + * that block readahead can cause. >> + */ >> + return NEEDS_RETRY; >> + } >> + } >> + >> /* >> * we might also expect a cc/ua if another LUN on the target >> * reported a UA with an ASC/ASCQ of 3F 0E - >> @@ -1944,9 +1956,19 @@ int scsi_decide_disposition(struct scsi_cmnd *scmd) >> * the request was not marked fast fail. Note that above, >> * even if the request is marked fast fail, we still requeue >> * for queue congestion conditions (QUEUE_FULL or BUSY) */ >> - if ((++scmd->retries) <= scmd->allowed >> - && !scsi_noretry_cmd(scmd)) { >> - return NEEDS_RETRY; >> + if ((++scmd->retries) <= scmd->allowed) { >> + /* >> + * but scsi_noretry_cmd() cannot override the >> + * expecting_media_change flag. >> + */ >> + if (!scsi_noretry_cmd(scmd) || >> + scmd->device->expecting_media_change) { >> + scmd->device->expecting_media_change = 0; >> + return NEEDS_RETRY; >> + } else { >> + /* marked fast fail and not expected. */ >> + return SUCCESS; >> + } >> } else { > > This may not matter... but it's worth pointing out that > expecting_media_change doesn't get cleared if ++scmd->retries > > scmd->allowed. absolutely worth pointing out and I'm not yet sure about that one. > > It also doesn't get cleared in cases where the device _doesn't_ > report a Unit Attention. true. but don't we set the flag for a future UA we don't yet know of? If we would want to clear it outside of a UA, I think we'd need to keep track of a suspend/resume cycle and if we see that we *had* successfully "done requests" after resuming, we could clear it... > > Alan Stern >