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=BAYES_00,DKIM_SIGNED, DKIM_VALID,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 248AFC11F66 for ; Tue, 29 Jun 2021 06:23:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ED2D261DC4 for ; Tue, 29 Jun 2021 06:23:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232041AbhF2G0C (ORCPT ); Tue, 29 Jun 2021 02:26:02 -0400 Received: from m43-7.mailgun.net ([69.72.43.7]:37875 "EHLO m43-7.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231881AbhF2G0B (ORCPT ); Tue, 29 Jun 2021 02:26:01 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1624947815; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=DdkTwy/6c3OcCt3JVBX/JqCoATNZP8AJdxUEwDuVA+g=; b=iAUjFz2Cueg+n4d4Zdec7p7LQfJJL1VoJnvEzT8Cm+NbiDCMB9jZydrr4R0bzAJWdrkIJJTS 80RtqudGUcW7+QUVigms4YLVqiOzRbYS/6Mm87TGrINj31jTRjsYzXES8ut+B3B0GTI+Ra5i dsZhe2khid0MVuz2oA2qVaZKQCk= X-Mailgun-Sending-Ip: 69.72.43.7 X-Mailgun-Sid: WyJlNmU5NiIsICJsaW51eC1zY3NpQHZnZXIua2VybmVsLm9yZyIsICJiZTllNGEiXQ== Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n06.prod.us-west-2.postgun.com with SMTP id 60dabc61ad0600eedeeb2904 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Tue, 29 Jun 2021 06:23:29 GMT Sender: cang=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 641A7C4360C; Tue, 29 Jun 2021 06:23:29 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: cang) by smtp.codeaurora.org (Postfix) with ESMTPSA id 21EE4C43460; Tue, 29 Jun 2021 06:23:28 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 29 Jun 2021 14:23:28 +0800 From: Can Guo To: Bart Van Assche Cc: Adrian Hunter , asutoshd@codeaurora.org, nguyenb@codeaurora.org, hongwus@codeaurora.org, ziqichen@codeaurora.org, linux-scsi@vger.kernel.org, kernel-team@android.com, Alim Akhtar , Avri Altman , "James E.J. Bottomley" , "Martin K. Petersen" , Stanley Chu , Bean Huo , Jaegeuk Kim , open list Subject: Re: [PATCH v4 06/10] scsi: ufs: Remove host_sem used in suspend/resume In-Reply-To: References: <1624433711-9339-1-git-send-email-cang@codeaurora.org> <1624433711-9339-8-git-send-email-cang@codeaurora.org> <9105f328ee6ce916a7f01027b0d28332@codeaurora.org> <1b351766a6e40d0df90b3adec964eb33@codeaurora.org> <3970b015e444c1f1714c7e7bd4c44651@codeaurora.org> <7ba226fe-789c-bf20-076b-cc635530db42@acm.org> Message-ID: <60a5496863100976b74d8c376c9e9cb0@codeaurora.org> X-Sender: cang@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 2021-06-29 01:31, Bart Van Assche wrote: > On 6/28/21 1:17 AM, Can Guo wrote: >> On 2021-06-25 01:11, Bart Van Assche wrote: >>> On 6/23/21 11:31 PM, Can Guo wrote: >>>> Using back host_sem in suspend_prepare()/resume_complete() won't >>>> have >>>> this problem of deadlock, right? >>> >>> Although that would solve the deadlock discussed in this email >>> thread, it >>> wouldn't solve the issue of potential adverse interactions of the UFS >>> error handler and the SCSI error handler running concurrently. >> >> I think I've explained it before, paste it here - >> >> ufshcd_eh_host_reset_handler() invokes ufshcd_err_handler() and >> flushes it, >> so SCSI error handler and UFS error handler can safely run together. > > That code path is the exception. Do you agree that the following three > functions all invoke the ufshcd_err_handler() function asynchronously? > * ufshcd_uic_pwr_ctrl() > * ufshcd_check_errors() > * ufshcd_abort() > I agree, but I don't see what's wrong with that. Any context can invoke ufs error handler asynchronously and ufs error handler prepare makes sure error handler can work safely, i.e., stopping PM ops/gating/scaling in error handler prepare makes sure no one shall call ufshcd_uic_pwr_ctrl() ever again. And ufshcd_check_errors() and ufshcd_abort() are OK to run concurrently with UFS error handler. >>> How about using the >>> standard approach for invoking the UFS error handler instead of using >>> a custom >>> mechanism, e.g. by using something like the (untested) patch below? >>> This >>> approach guarantees that the UFS error handler is only activated >>> after >>> all >>> pending SCSI commands have failed or timed out and also guarantees >>> that no new >>> SCSI commands will be queued while the UFS error handler is in >>> progress (see >>> also scsi_host_queue_ready()). >> >> Per my understanding, SCSI error handling is scsi cmd based, meaning >> it >> only works when certain SCSI cmds failed [ ... ] > That is not completely correct. The SCSI error handler is activated if > either all pending commands have failed or if it is scheduled > explicitly. Please take a look at the host_eh_scheduled member > variable, > how it is used and also at scsi_schedule_eh(). The scsi_schedule_eh() > function was introduced in 2006 and that the ATA code uses it since > then > to activate the SCSI error handler even if no commands are pending. See > also the patch "SCSI: make scsi_implement_eh() generic API for SCSI > transports". > >> However, most UFS (UIC) errors happens during gear scaling, clk gating >> and suspend/resume (due to power mode changes and/or hibern8 >> enter/exit), during which there is NO scsi cmds in UFS driver at all >> (because these contexts start only when there is no ongoing data >> transactions). > > Activating the SCSI error handler if no SCSI commands are in progress > is > supported by scsi_schedule_eh(). > >> Thus, scsi_unjam_host() won't even call scsi_eh_ready_devs() because >> scsi_eh_get_sense() always returns TRUE in these cases (eh_work_q is >> empty). > > Please take another look at the patch in my previous message. There is > a > scsi_transport_template instance in that patch. The eh_strategy_handler > defined in a SCSI transport template is called *instead* of > scsi_unjam_host(). In other words, scsi_unjam_host() won't be called if > my patch would be applied to the UFS driver. > > Please let me know if you need more information. Sorry that I missed the change of scsi_transport_template() in your previous message. I can understand that you want to invoke UFS error hander by invoking SCSI error handler, but I didn't go that far because I saw you changed pm_runtime_get_sync() to pm_runtime_get_noresume() in ufs error handler prepare. How can that change make sure that the device is not suspending or resuming while error handler is running? Thanks, Can Guo. > > Bart.