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Message-ID: <525e4f67-f471-54a6-aaea-b3772a550af1@acm.org>
Date: Sat, 25 Jan 2020 19:29:55 -0800
From: Bart Van Assche <bvanassche@....org>
To: Can Guo <cang@...eaurora.org>, asutoshd@...eaurora.org,
nguyenb@...eaurora.org, hongwus@...eaurora.org,
rnayak@...eaurora.org, linux-scsi@...r.kernel.org,
kernel-team@...roid.com, saravanak@...gle.com, salyzyn@...gle.com
Cc: Sayali Lokhande <sayalil@...eaurora.org>,
Alim Akhtar <alim.akhtar@...sung.com>,
Avri Altman <avri.altman@....com>,
Pedro Sousa <pedrom.sousa@...opsys.com>,
"James E.J. Bottomley" <jejb@...ux.ibm.com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
Stanley Chu <stanley.chu@...iatek.com>,
Bean Huo <beanhuo@...ron.com>,
Venkat Gopalakrishnan <venkatg@...eaurora.org>,
Tomas Winkler <tomas.winkler@...el.com>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/8] scsi: ufs: Flush exception event before suspend
On 2020-01-22 23:25, Can Guo wrote:
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 1201578..c2de29f 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -4760,8 +4760,15 @@ static void ufshcd_slave_destroy(struct scsi_device *sdev)
> * UFS device needs urgent BKOPs.
> */
> if (!hba->pm_op_in_progress &&
> - ufshcd_is_exception_event(lrbp->ucd_rsp_ptr))
> - schedule_work(&hba->eeh_work);
> + ufshcd_is_exception_event(lrbp->ucd_rsp_ptr)) {
> + /*
> + * Prevent suspend once eeh_work is scheduled
> + * to avoid deadlock between ufshcd_suspend
> + * and exception event handler.
> + */
> + if (schedule_work(&hba->eeh_work))
> + pm_runtime_get_noresume(hba->dev);
> + }
Please combine the two logical tests with "&&" instead of nesting two
if-statements inside each other.
> break;
> case UPIU_TRANSACTION_REJECT_UPIU:
> /* TODO: handle Reject UPIU Response */
> @@ -5215,7 +5222,14 @@ static void ufshcd_exception_event_handler(struct work_struct *work)
>
> out:
> scsi_unblock_requests(hba->host);
> - pm_runtime_put_sync(hba->dev);
> + /*
> + * pm_runtime_get_noresume is called while scheduling
> + * eeh_work to avoid suspend racing with exception work.
> + * Hence decrement usage counter using pm_runtime_put_noidle
> + * to allow suspend on completion of exception event handler.
> + */
> + pm_runtime_put_noidle(hba->dev);
> + pm_runtime_put(hba->dev);
> return;
> }
>
> @@ -7901,6 +7915,7 @@ static int ufshcd_suspend(struct ufs_hba *hba, enum ufs_pm_op pm_op)
> goto enable_gating;
> }
>
> + flush_work(&hba->eeh_work);
> ret = ufshcd_link_state_transition(hba, req_link_state, 1);
> if (ret)
> goto set_dev_active;
I think this patch introduces a new race condition, namely the following:
- ufshcd_slave_destroy() tests pm_op_in_progress and reads the value
zero from that variable.
- ufshcd_suspend() sets hba->pm_op_in_progress to one.
- ufshcd_slave_destroy() calls schedule_work().
How about fixing this race condition by calling
pm_runtime_get_noresume() before checking pm_op_in_progress and by
reallowing resume if no work is scheduled?
Thanks,
Bart.
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