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Mon, 03 Aug 2020 11:50:16 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 487E6C43395; Mon, 3 Aug 2020 11:50:15 +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 A93D1C433C6; Mon, 3 Aug 2020 11:50:13 +0000 (UTC) MIME-Version: 1.0 Date: Mon, 03 Aug 2020 19:50:13 +0800 From: Can Guo To: Stanley Chu Subject: Re: [PATCH v7] scsi: ufs: Quiesce all scsi devices before shutdown In-Reply-To: <20200803100448.2738-1-stanley.chu@mediatek.com> References: <20200803100448.2738-1-stanley.chu@mediatek.com> Message-ID: X-Sender: cang@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200803_075025_678365_EAB75A94 X-CRM114-Status: GOOD ( 27.78 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: jiajie.hao@mediatek.com, linux-scsi@vger.kernel.org, martin.petersen@oracle.com, andy.teng@mediatek.com, jejb@linux.ibm.com, chun-hung.wu@mediatek.com, kuohong.wang@mediatek.com, linux-kernel@vger.kernel.org, asutoshd@codeaurora.org, avri.altman@wdc.com, linux-mediatek@lists.infradead.org, peter.wang@mediatek.com, alim.akhtar@samsung.com, matthias.bgg@gmail.com, beanhuo@micron.com, chaotian.jing@mediatek.com, cc.chou@mediatek.com, linux-arm-kernel@lists.infradead.org, bvanassche@acm.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Stanley, On 2020-08-03 18:04, Stanley Chu wrote: > Currently I/O request could be still submitted to UFS device while > UFS is working on shutdown flow. This may lead to racing as below > scenarios and finally system may crash due to unclocked register > accesses. > > To fix this kind of issues, in ufshcd_shutdown(), > > 1. Use pm_runtime_get_sync() instead of resuming UFS device by > ufshcd_runtime_resume() "internally" to let runtime PM framework > manage and prevent concurrent runtime operations by incoming I/O > requests. > > 2. Specifically quiesce all SCSI devices to block all I/O requests > after device is resumed. > > Example of racing scenario: While UFS device is runtime-suspended > > Thread #1: Executing UFS shutdown flow, e.g., > ufshcd_suspend(UFS_SHUTDOWN_PM) > > Thread #2: Executing runtime resume flow triggered by I/O request, > e.g., ufshcd_resume(UFS_RUNTIME_PM) > > This breaks the assumption that UFS PM flows can not be running > concurrently and some unexpected racing behavior may happen. > > Signed-off-by: Stanley Chu > --- > Changes: > - Since v6: > - Do quiesce to all SCSI devices. > - Since v4: > - Use pm_runtime_get_sync() instead of resuming UFS device by > ufshcd_runtime_resume() "internally". > --- > drivers/scsi/ufs/ufshcd.c | 27 ++++++++++++++++++++++----- > 1 file changed, 22 insertions(+), 5 deletions(-) > > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c > index 307622284239..7cb220b3fde0 100644 > --- a/drivers/scsi/ufs/ufshcd.c > +++ b/drivers/scsi/ufs/ufshcd.c > @@ -8640,6 +8640,7 @@ EXPORT_SYMBOL(ufshcd_runtime_idle); > int ufshcd_shutdown(struct ufs_hba *hba) > { > int ret = 0; > + struct scsi_target *starget; > > if (!hba->is_powered) > goto out; > @@ -8647,11 +8648,27 @@ int ufshcd_shutdown(struct ufs_hba *hba) > if (ufshcd_is_ufs_dev_poweroff(hba) && ufshcd_is_link_off(hba)) > goto out; > > - if (pm_runtime_suspended(hba->dev)) { > - ret = ufshcd_runtime_resume(hba); > - if (ret) > - goto out; > - } > + /* > + * Let runtime PM framework manage and prevent concurrent runtime > + * operations with shutdown flow. > + */ > + pm_runtime_get_sync(hba->dev); > + > + /* > + * Quiesce all SCSI devices to prevent any non-PM requests sending > + * from block layer during and after shutdown. > + * > + * Here we can not use blk_cleanup_queue() since PM requests > + * (with BLK_MQ_REQ_PREEMPT flag) are still required to be sent > + * through block layer. Therefore SCSI command queued after the > + * scsi_target_quiesce() call returned will block until > + * blk_cleanup_queue() is called. > + * > + * Besides, scsi_target_"un"quiesce (e.g., scsi_target_resume) can > + * be ignored since shutdown is one-way flow. > + */ > + list_for_each_entry(starget, &hba->host->__targets, siblings) > + scsi_target_quiesce(starget); > Sorry for misleading you to scsi_target_quiesce(), maybe below is better. shost_for_each_device(sdev, hba->host) scsi_device_quiesce(sdev); We may need to discuss more about this quiesce part since I missed something. After we quiesce the scsi devices, only PM requests are allowed, but it is still not safe: [1] PM requests can still pass through, [2] there can be tasks/reqs present in doorbells before the devices are quiesced. So, these tasks/reqs in [1] and [2] can still be flying in parallel while ufshcd_suspend is running. How about only quiescing the UFS device well known scsi device but using freeze_queue to the other scsi devices? blk_mq_freeze_queue can eliminate the risks mentioned in [1] and [2]. shost_for_each_device(sdev, hba->host) { if (sdev == hba->sdev_ufs_device) scsi_device_quiesce(sdev); else blk_mq_freeze_queue(sdev->request_queue); } IF blk_mq_freeze_queue is not allowed to be used by LLD (I think we can use it as I recalled Bart used to use it in one of his changes to UFS scaling), we may need to make changes like below. [1] is to make sure no more PM requests sent to scsi devices, [2] is make sure doorbells are cleared before invoke ufshcd_suspend. shost_for_each_device(sdev, hba->host) { scsi_autopm_get_device(sdev); [1] scsi_device_quiesce(sdev); } ufshcd_wait_for_doorbell_clr(hba, U64_MAX); [2] Please let me know your ideas, thanks! Regards, Can Guo. > ret = ufshcd_suspend(hba, UFS_SHUTDOWN_PM); > out: _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel