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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04846C433F5 for ; Wed, 3 Nov 2021 14:04:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D49A061130 for ; Wed, 3 Nov 2021 14:04:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231343AbhKCOHY (ORCPT ); Wed, 3 Nov 2021 10:07:24 -0400 Received: from mga05.intel.com ([192.55.52.43]:14143 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230527AbhKCOHY (ORCPT ); Wed, 3 Nov 2021 10:07:24 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10156"; a="317703792" X-IronPort-AV: E=Sophos;i="5.87,206,1631602800"; d="scan'208";a="317703792" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Nov 2021 07:03:40 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.87,206,1631602800"; d="scan'208";a="541695514" Received: from ahunter-desktop.fi.intel.com (HELO [10.237.72.76]) ([10.237.72.76]) by fmsmga008.fm.intel.com with ESMTP; 03 Nov 2021 07:03:38 -0700 Subject: Re: [PATCH 2/2] scsi: ufs: Fix a deadlock in the error handler To: Bart Van Assche , "Martin K . Petersen" Cc: Jaegeuk Kim , linux-scsi@vger.kernel.org, "James E.J. Bottomley" , Can Guo , Bean Huo , Stanley Chu , Asutosh Das References: <20211103000529.1549411-1-bvanassche@acm.org> <20211103000529.1549411-3-bvanassche@acm.org> <82dffddc-15e8-dc1a-abda-e84e7e441d87@intel.com> From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki Message-ID: Date: Wed, 3 Nov 2021 16:03:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 03/11/2021 15:40, Bart Van Assche wrote: > On 11/2/21 23:56, Adrian Hunter wrote: >> On 03/11/2021 02:05, Bart Van Assche wrote: >>> The following deadlock has been observed on a test setup: >>> * All tags allocated. >>> * The SCSI error handler calls ufshcd_eh_host_reset_handler() >>> * ufshcd_eh_host_reset_handler() queues work that calls ufshcd_err_handler() >>> * ufshcd_err_handler() locks up as follows: >>> >>> Workqueue: ufs_eh_wq_0 ufshcd_err_handler.cfi_jt >>> Call trace: >>>   __switch_to+0x298/0x5d8 >>>   __schedule+0x6cc/0xa94 >>>   schedule+0x12c/0x298 >>>   blk_mq_get_tag+0x210/0x480 >>>   __blk_mq_alloc_request+0x1c8/0x284 >>>   blk_get_request+0x74/0x134 >>>   ufshcd_exec_dev_cmd+0x68/0x640 >>>   ufshcd_verify_dev_init+0x68/0x35c >>>   ufshcd_probe_hba+0x12c/0x1cb8 >>>   ufshcd_host_reset_and_restore+0x88/0x254 >>>   ufshcd_reset_and_restore+0xd0/0x354 >>>   ufshcd_err_handler+0x408/0xc58 >>>   process_one_work+0x24c/0x66c >>>   worker_thread+0x3e8/0xa4c >>>   kthread+0x150/0x1b4 >>>   ret_from_fork+0x10/0x30 >>> >>> Fix this lockup by making ufshcd_exec_dev_cmd() allocate a reserved >>> request. >> >> It is worth noting that the error handler itself could always find >> a free slot, either by waiting for one, or by taking the reset >> path which clears all slots. > > I do not agree. As mentioned in the patch description, this patch is a fix for a scenario in which ufshcd_eh_host_reset_handler() waits until ufshcd_err_handler() finishes. ufshcd_err_handler() does not finish since there are no tags and no tags will be freed since that is the responsibility of ufshcd_eh_host_reset_handler() but it is blocked ... I am referring to the host controller slots, not block layer tags. The error handler does not need a free tag, it only needs a free slot.