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Date:   Wed, 16 May 2018 14:13:04 -0700
From:   Subhash Jadavani <subhashj@codeaurora.org>
To:     Asutosh Das <asutoshd@codeaurora.org>
Cc:     cang@codeaurora.org, vivek.gautam@codeaurora.org,
        rnayak@codeaurora.org, vinholikatti@gmail.com,
        jejb@linux.vnet.ibm.com, martin.petersen@oracle.com,
        linux-mmc@vger.kernel.org, linux-scsi@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-scsi-owner@vger.kernel.org
Subject: Re: [PATCH v2 06/10] scsi: ufs: add reference counting for scsi block
 requests
In-Reply-To: <3d524952ffe2c0a14c92f5e322aed5d2c24c2832.1525343531.git.asutoshd@codeaurora.org>
References: <cover.1525343531.git.asutoshd@codeaurora.org>
 <3d524952ffe2c0a14c92f5e322aed5d2c24c2832.1525343531.git.asutoshd@codeaurora.org>
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On 2018-05-03 04:07, Asutosh Das wrote:
> From: Subhash Jadavani <subhashj@codeaurora.org>
> 
> Currently we call the scsi_block_requests()/scsi_unblock_requests()
> whenever we want to block/unblock scsi requests but as there is no
> reference counting, nesting of these calls could leave us in undesired
> state sometime. Consider following call flow sequence:
> 1. func1() calls scsi_block_requests() but calls func2() before
>    calling scsi_unblock_requests()
> 2. func2() calls scsi_block_requests()
> 3. func2() calls scsi_unblock_requests()
> 4. func1() calls scsi_unblock_requests()
> 
> As there is no reference counting, we will have scsi requests unblocked
> after #3 instead of it to be unblocked only after #4. Though we may not
> have failures seen with this, we might run into some failures in 
> future.
> Better solution would be to fix this by adding reference counting.
> 
> Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
> Signed-off-by: Can Guo <cang@codeaurora.org>
> Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
> ---
>  drivers/scsi/ufs/ufshcd.c | 28 ++++++++++++++++++++--------
>  drivers/scsi/ufs/ufshcd.h |  2 ++
>  2 files changed, 22 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index dfeb194..c35a076 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -264,6 +264,18 @@ static inline void ufshcd_disable_irq(struct 
> ufs_hba *hba)
>  	}
>  }
> 
> +static void ufshcd_scsi_unblock_requests(struct ufs_hba *hba)
> +{
> +	if (atomic_dec_and_test(&hba->scsi_block_reqs_cnt))
> +		scsi_unblock_requests(hba->host);
> +}
> +
> +static void ufshcd_scsi_block_requests(struct ufs_hba *hba)
> +{
> +	if (atomic_inc_return(&hba->scsi_block_reqs_cnt) == 1)
> +		scsi_block_requests(hba->host);
> +}
> +
>  /* replace non-printable or non-ASCII characters with spaces */
>  static inline void ufshcd_remove_non_printable(char *val)
>  {
> @@ -1077,12 +1089,12 @@ static int ufshcd_clock_scaling_prepare(struct
> ufs_hba *hba)
>  	 * make sure that there are no outstanding requests when
>  	 * clock scaling is in progress
>  	 */
> -	scsi_block_requests(hba->host);
> +	ufshcd_scsi_block_requests(hba);
>  	down_write(&hba->clk_scaling_lock);
>  	if (ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US)) {
>  		ret = -EBUSY;
>  		up_write(&hba->clk_scaling_lock);
> -		scsi_unblock_requests(hba->host);
> +		ufshcd_scsi_unblock_requests(hba);
>  	}
> 
>  	return ret;
> @@ -1091,7 +1103,7 @@ static int ufshcd_clock_scaling_prepare(struct
> ufs_hba *hba)
>  static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
>  {
>  	up_write(&hba->clk_scaling_lock);
> -	scsi_unblock_requests(hba->host);
> +	ufshcd_scsi_unblock_requests(hba);
>  }
> 
>  /**
> @@ -1411,7 +1423,7 @@ static void ufshcd_ungate_work(struct work_struct 
> *work)
>  		hba->clk_gating.is_suspended = false;
>  	}
>  unblock_reqs:
> -	scsi_unblock_requests(hba->host);
> +	ufshcd_scsi_unblock_requests(hba);
>  }
> 
>  /**
> @@ -1467,7 +1479,7 @@ int ufshcd_hold(struct ufs_hba *hba, bool async)
>  		 * work and to enable clocks.
>  		 */
>  	case CLKS_OFF:
> -		scsi_block_requests(hba->host);
> +		ufshcd_scsi_block_requests(hba);
>  		hba->clk_gating.state = REQ_CLKS_ON;
>  		trace_ufshcd_clk_gating(dev_name(hba->dev),
>  					hba->clk_gating.state);
> @@ -5192,7 +5204,7 @@ static void ufshcd_err_handler(struct work_struct 
> *work)
> 
>  out:
>  	spin_unlock_irqrestore(hba->host->host_lock, flags);
> -	scsi_unblock_requests(hba->host);
> +	ufshcd_scsi_unblock_requests(hba);
>  	ufshcd_release(hba);
>  	pm_runtime_put_sync(hba->dev);
>  }
> @@ -5294,7 +5306,7 @@ static void ufshcd_check_errors(struct ufs_hba 
> *hba)
>  		/* handle fatal errors only when link is functional */
>  		if (hba->ufshcd_state == UFSHCD_STATE_OPERATIONAL) {
>  			/* block commands from scsi mid-layer */
> -			scsi_block_requests(hba->host);
> +			ufshcd_scsi_block_requests(hba);
> 
>  			hba->ufshcd_state = UFSHCD_STATE_EH_SCHEDULED;
> 
> @@ -8017,7 +8029,7 @@ int ufshcd_init(struct ufs_hba *hba, void
> __iomem *mmio_base, unsigned int irq)
> 
>  	/* Hold auto suspend until async scan completes */
>  	pm_runtime_get_sync(dev);
> -
> +	atomic_set(&hba->scsi_block_reqs_cnt, 0);
>  	/*
>  	 * We are assuming that device wasn't put in sleep/power-down
>  	 * state exclusively during the boot stage before kernel.
> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> index 0417c42..76c31d5 100644
> --- a/drivers/scsi/ufs/ufshcd.h
> +++ b/drivers/scsi/ufs/ufshcd.h
> @@ -498,6 +498,7 @@ struct ufs_stats {
>   * @urgent_bkops_lvl: keeps track of urgent bkops level for device
>   * @is_urgent_bkops_lvl_checked: keeps track if the urgent bkops level 
> for
>   *  device is known or not.
> + * @scsi_block_reqs_cnt: reference counting for scsi block requests
>   */
>  struct ufs_hba {
>  	void __iomem *mmio_base;
> @@ -698,6 +699,7 @@ struct ufs_hba {
> 
>  	struct rw_semaphore clk_scaling_lock;
>  	struct ufs_desc_size desc_size;
> +	atomic_t scsi_block_reqs_cnt;
>  };
> 
>  /* Returns true if clocks can be gated. Otherwise false */

Looks good to me.

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