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=-9.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 F3D35C2D0A3 for ; Tue, 3 Nov 2020 13:28:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA441216C4 for ; Tue, 3 Nov 2020 13:28:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="tsC0FgZj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729246AbgKCN21 (ORCPT ); Tue, 3 Nov 2020 08:28:27 -0500 Received: from z5.mailgun.us ([104.130.96.5]:22061 "EHLO z5.mailgun.us" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729229AbgKCN2Z (ORCPT ); Tue, 3 Nov 2020 08:28:25 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1604410105; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=JLjIZJZw1u9HJgVMWdn4LPLwRFKRMpegIpRTqok6leY=; b=tsC0FgZjitOhS94IAN0g4cU5Row3+l55vWSI4f5SBUgA2A3HjdTp+Bw0OLHZRHcdcH8fiiD0 DYlQCC8qzbZ3BHB40+Ay848Wq84pmWWfdxBgz9na74inxizPpwrIMOJ5RDZOVEJR33PwnD3v Y9g8qcQbI504wdvzdr68ZHckDvc= X-Mailgun-Sending-Ip: 104.130.96.5 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 5fa15af7875877e3edaa822f (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Tue, 03 Nov 2020 13:28:23 GMT Sender: cang=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id A0073C38591; Tue, 3 Nov 2020 10:01:07 +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 69B04C38586; Tue, 3 Nov 2020 10:01:02 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 03 Nov 2020 18:01:01 +0800 From: Can Guo To: Stanley Chu Cc: asutoshd@codeaurora.org, nguyenb@codeaurora.org, hongwus@codeaurora.org, rnayak@codeaurora.org, linux-scsi@vger.kernel.org, kernel-team@android.com, saravanak@google.com, salyzyn@google.com, Alim Akhtar , Avri Altman , "James E.J. Bottomley" , "Martin K. Petersen" , Bean Huo , Bart Van Assche , open list Subject: Re: [PATCH v1 1/2] scsi: ufs: Fix unbalanced scsi_block_reqs_cnt caused by ufshcd_hold() In-Reply-To: <1604387262.13152.2.camel@mtkswgap22> References: <1604384682-15837-1-git-send-email-cang@codeaurora.org> <1604384682-15837-2-git-send-email-cang@codeaurora.org> <1604387262.13152.2.camel@mtkswgap22> Message-ID: <09c5d4d31a0bd9bed99815cfbf51aaad@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 2020-11-03 15:07, Stanley Chu wrote: > Hi Can, > > On Mon, 2020-11-02 at 22:24 -0800, Can Guo wrote: >> The scsi_block_reqs_cnt increased in ufshcd_hold() is supposed to be >> decreased back in ufshcd_ungate_work() in a paired way. However, if >> specific ufshcd_hold/release sequences are met, it is possible that >> scsi_block_reqs_cnt is increased twice but only one ungate work is >> queued. To make sure scsi_block_reqs_cnt is handled by ufshcd_hold() >> and > > Just curious that how could this be possible? Would you have some > failed > examples? > [1] One gate_work() is in the workqueue, not yet executed, now clk state == REQ_CLKS_OFF. [2] ufshcd_queuecommand() calls ufshcd_hold(async == ture) -> active_req++ -> scsi_block_reqs_cnt++ -> REQ_CLKS_ON -> queue ungate work -> active_req-- -> return -EAGAIN. [3] Now gate_work() starts to run, but since the clk state is REQ_CLKS_ON, gate_work() just sets clk state to CLKS_ON and bail. [3] Someone calls ufshcd_hold(async == false) -> do something -> ufshcd_release() -> clk state is changed to REQ_CLKS_OFF. Note that, till now, ungate_work() is still in the work queue, not executed yet. [4] Now, if someone calls ufshcd_hold(), we will hit the issue. Above sequence is a very common clk gate/ungate sequence. The issue is because ungate_work is queued but cannot be executed in time. In my case, I see the ungate_work is somehow delayed for about 150ms. This change has been tested by customers on multiple platforms. And you can tell from the code that it won't break anything. :) Thanks, Can Guo. >> ufshcd_ungate_work() in a paired way, increase it only if queue_work() >> returns true. >> >> Signed-off-by: Can Guo >> Reviewed-by: Hongwu Su >> --- >> drivers/scsi/ufs/ufshcd.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c >> index 847f355..efa7d86 100644 >> --- a/drivers/scsi/ufs/ufshcd.c >> +++ b/drivers/scsi/ufs/ufshcd.c >> @@ -1634,12 +1634,12 @@ int ufshcd_hold(struct ufs_hba *hba, bool >> async) >> */ >> /* fallthrough */ >> case CLKS_OFF: >> - ufshcd_scsi_block_requests(hba); >> hba->clk_gating.state = REQ_CLKS_ON; >> trace_ufshcd_clk_gating(dev_name(hba->dev), >> hba->clk_gating.state); >> - queue_work(hba->clk_gating.clk_gating_workq, >> - &hba->clk_gating.ungate_work); >> + if (queue_work(hba->clk_gating.clk_gating_workq, >> + &hba->clk_gating.ungate_work)) >> + ufshcd_scsi_block_requests(hba); >> /* >> * fall through to check if we should wait for this >> * work to be done or not. > > Thanks, > Stanley Chu