linux-kernel - Re: [PATCH v2 2/4] scsi: ufs: Fix imbalanced scsi_block_reqs_cnt caused by ufshcd

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Date:   Mon, 13 Jul 2020 20:41:49 -0700
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:     Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....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>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] scsi: ufs: Fix imbalanced scsi_block_reqs_cnt
 caused by ufshcd_hold()

On 2020-07-13 19:28, 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
> ufshcd_ungate_work() in a paired way, increase it only if queue_work()
> returns true.
> 
> Signed-off-by: Can Guo <cang@...eaurora.org>
> ---
>  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 ebf7a95..33214bb 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1611,12 +1611,12 @@ 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.

Since "ungate_work" involves calling ufshcd_scsi_unblock_requests() and
since this patch changes the order in which ufshcd_scsi_block_requests()
and queue_work() are called, I think this patch introduces a race
condition. Has it been considered to leave the ufshcd_scsi_block_requests()
call where it is and to call ufshcd_scsi_unblock_requests() if
queue_work() fails?

Thanks,

Bart.