On 2020-07-22 02:14, Stanley Chu wrote:
> Hi Bart,
>
> On Sat, 2020-07-18 at 13:30 -0700, Bart Van Assche wrote:
>> On 2020-07-17 00:39, Lee Sang Hyun wrote:
>>> - ret = scsi_execute(sdp, cmd, DMA_NONE, NULL, 0, NULL, &sshdr,
>>> - START_STOP_TIMEOUT, 0, 0, RQF_PM, NULL);
>>> - if (ret) {
>>> - sdev_printk(KERN_WARNING, sdp,
>>> - "START_STOP failed for power mode: %d, result %x\n",
>>> - pwr_mode, ret);
>>> - if (driver_byte(ret) == DRIVER_SENSE)
>>> - scsi_print_sense_hdr(sdp, NULL, &sshdr);
>>> + for (retries = 0; retries < SSU_RETRIES; retries++) {
>>> + ret = scsi_execute(sdp, cmd, DMA_NONE, NULL, 0, NULL, &sshdr,
>>> + START_STOP_TIMEOUT, 0, 0, RQF_PM, NULL);
>>> + if (ret) {
>>> + sdev_printk(KERN_WARNING, sdp,
>>> + "START_STOP failed for power mode: %d, result %x\n",
>>> + pwr_mode, ret);
>>> + if (driver_byte(ret) == DRIVER_SENSE)
>>> + scsi_print_sense_hdr(sdp, NULL, &sshdr);
>>> + } else {
>>> + break;
>>> + }
>>
>> The ninth argument of scsi_execute() is called 'retries'. Wouldn't it be
>> better to pass a nonzero value as the 'retries' argument of
>> scsi_execute() instead of adding a loop around the scsi_execute() call?
>
> If a SCSI command issued via scsi_execute() encounters "timeout" or
> "check condition", scsi_noretry_cmd() will return 1 (true) because
> blk_rq_is_passthrough() is true due to REQ_OP_SCSI_IN or REQ_OP_SCSI_OUT
> flag was set to this SCSI command by scsi_execute(). Therefore even a
> non-zero 'retries' value is assigned while calling scsi_execute(), the
> failed command has no chance to be retried since the decision will be
> no-retry by scsi_noretry_cmd().
>
> (Take command timeout as example)
> scsi_times_out()->scsi_abort_command()->scmd_eh_abort_handler(), here
> scsi_noretry_cmd() returns 1, and then command will be finished (with
> error code) without retry.
>
> In scsi_noretry_cmd(), there is a comment message in section
> "check_type" as below
>
> /*
> * assume caller has checked sense and determined
> * the check condition was retryable.
> */
>
> I am not sure if "timeout" and "check condition" cases in such SCSI
> commands issued via scsi_execute() are specially designed to be unable
> to retry.
>
> Would you have any suggestions if LLD drivers would like to retry these
> kinds of SCSI commands?
How about summarizing the above explanation of why the 'retry' argument
of scsi_execute() cannot be used in a two or three line comment and to
add that comment above the loop introduced by this patch?
Thanks,
Bart.
