Re: [PATCH v3 15/17] scsi: ufs: Stop using the clock scaling lock in the error handler

[Adrian Hunter <adrian.hunter@intel.com>]

On 01/12/2021 01:33, Bart Van Assche wrote:
> Instead of locking and unlocking the clock scaling lock, surround the
> command queueing code with an RCU reader lock and call synchronize_rcu().
> This patch prepares for removal of the clock scaling lock.
> 
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>

> ---
>  drivers/scsi/ufs/ufshcd.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 074ea9ae54e0..c4cf5c4b4893 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -2684,6 +2684,12 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
>  	if (!down_read_trylock(&hba->clk_scaling_lock))
>  		return SCSI_MLQUEUE_HOST_BUSY;
>  
> +	/*
> +	 * Allows the UFS error handler to wait for prior ufshcd_queuecommand()
> +	 * calls.
> +	 */
> +	rcu_read_lock();
> +
>  	switch (hba->ufshcd_state) {
>  	case UFSHCD_STATE_OPERATIONAL:
>  		break;
> @@ -2762,7 +2768,10 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
>  	}
>  
>  	ufshcd_send_command(hba, tag);
> +
>  out:
> +	rcu_read_unlock();
> +
>  	up_read(&hba->clk_scaling_lock);
>  
>  	if (ufs_trigger_eh()) {
> @@ -5951,8 +5960,7 @@ static void ufshcd_err_handling_prepare(struct ufs_hba *hba)
>  	}
>  	ufshcd_scsi_block_requests(hba);
>  	/* Drain ufshcd_queuecommand() */
> -	down_write(&hba->clk_scaling_lock);
> -	up_write(&hba->clk_scaling_lock);
> +	synchronize_rcu();
>  	cancel_work_sync(&hba->eeh_work);
>  }
>  
>