Re: [REVIEW PATCH] scsi: Add 'retry_timeout' to avoid infinitecommand retry

[James Bottomley]

On Wed, 2014-02-05 at 14:47 +0900, Eiichi Tsukata wrote:
> Currently, scsi error handling in scsi_decide_disposition() tries to
> unconditionally requeue scsi command when device keeps some error state.
> This is because retryable errors are thought to be temporary and the scsi
> device will soon recover from those errors. Normally, such retry policy is
> appropriate because the device will soon recover from temporary error state.

This description isn't very descriptive.  I presume you're talking about
the ADD_TO_MLQUEUE return from scsi_decide_disposition()?

> But there is no guarantee that device is able to recover from error state
> immediately. Some hardware error may prevent device from recovering.
> Therefore hardware error can results in infinite command retry loop.

If you're talking about ADD_TO_MLQUEUE, I don't believe this is correct:
there's a test in scsi_softirq_done() that makes sure the maximum
lifetime is retries*timeout and fails the command after that.

James


> This patchs adds 'retry_timeout' sysfs attribute which limits the retry time
> of each scsi command. Once scsi command retry time is longer than this timeout,
> the command is treated as failure. 'retry_timeout' is set to '0' by default
> which means no timeout set.
> 
> Signed-off-by: Eiichi Tsukata <eiichi.tsukata.xh@xxxxxxxxxxx>
> Cc: "James E.J. Bottomley" <JBottomley@xxxxxxxxxxxxx>
> Cc: linux-scsi@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>  drivers/scsi/scsi_lib.c    | 22 +++++++++++++++++++++-
>  drivers/scsi/scsi_scan.c   |  1 +
>  drivers/scsi/scsi_sysfs.c  | 32 ++++++++++++++++++++++++++++++++
>  include/scsi/scsi.h        |  1 +
>  include/scsi/scsi_device.h |  1 +
>  5 files changed, 56 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 7bd7f0d..a9db69e 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1492,6 +1492,23 @@ static void scsi_kill_request(struct request *req, struct request_queue *q)
>  	blk_complete_request(req);
>  }
>  
> +/*
> + * Check if scsi command excessed retry timeout
> + */
> +static int scsi_retry_timed_out(struct scsi_cmnd *cmd)
> +{
> +	unsigned int retry_timeout;
> +
> +	retry_timeout = cmd->device->retry_timeout;
> +	if (retry_timeout &&
> +	    time_before(cmd->jiffies_at_alloc + retry_timeout, jiffies)) {
> +		scmd_printk(KERN_INFO, cmd, "retry timeout\n");
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
>  static void scsi_softirq_done(struct request *rq)
>  {
>  	struct scsi_cmnd *cmd = rq->special;
> @@ -1512,7 +1529,10 @@ static void scsi_softirq_done(struct request *rq)
>  			    wait_for/HZ);
>  		disposition = SUCCESS;
>  	}
> -			
> +
> +	if (scsi_retry_timed_out(cmd))
> +		disposition = FAILED;
> +
>  	scsi_log_completion(cmd, disposition);
>  
>  	switch (disposition) {
> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> index 307a811..4ab044a 100644
> --- a/drivers/scsi/scsi_scan.c
> +++ b/drivers/scsi/scsi_scan.c
> @@ -925,6 +925,7 @@ static int scsi_add_lun(struct scsi_device *sdev, unsigned char *inq_result,
>  		sdev->no_dif = 1;
>  
>  	sdev->eh_timeout = SCSI_DEFAULT_EH_TIMEOUT;
> +	sdev->retry_timeout = SCSI_DEFAULT_RETRY_TIMEOUT;
>  
>  	if (*bflags & BLIST_SKIP_VPD_PAGES)
>  		sdev->skip_vpd_pages = 1;
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index 8ff62c2..eaa2118 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -627,6 +627,37 @@ sdev_store_eh_timeout(struct device *dev, struct device_attribute *attr,
>  static DEVICE_ATTR(eh_timeout, S_IRUGO | S_IWUSR, sdev_show_eh_timeout, sdev_store_eh_timeout);
>  
>  static ssize_t
> +sdev_show_retry_timeout(struct device *dev,
> +			struct device_attribute *attr, char *buf)
> +{
> +	struct scsi_device *sdev;
> +	sdev = to_scsi_device(dev);
> +	return snprintf(buf, 20, "%u\n", sdev->retry_timeout / HZ);
> +}
> +
> +static ssize_t
> +sdev_store_retry_timeout(struct device *dev, struct device_attribute *attr,
> +			 const char *buf, size_t count)
> +{
> +	struct scsi_device *sdev;
> +	unsigned int retry_timeout;
> +	int err;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EACCES;
> +
> +	sdev = to_scsi_device(dev);
> +	err = kstrtouint(buf, 10, &retry_timeout);
> +	if (err)
> +		return err;
> +	sdev->retry_timeout = retry_timeout * HZ;
> +
> +	return count;
> +}
> +static DEVICE_ATTR(retry_timeout, S_IRUGO | S_IWUSR,
> +		   sdev_show_retry_timeout, sdev_store_retry_timeout);
> +
> +static ssize_t
>  store_rescan_field (struct device *dev, struct device_attribute *attr,
>  		    const char *buf, size_t count)
>  {
> @@ -797,6 +828,7 @@ static struct attribute *scsi_sdev_attrs[] = {
>  	&dev_attr_state.attr,
>  	&dev_attr_timeout.attr,
>  	&dev_attr_eh_timeout.attr,
> +	&dev_attr_retry_timeout.attr,
>  	&dev_attr_iocounterbits.attr,
>  	&dev_attr_iorequest_cnt.attr,
>  	&dev_attr_iodone_cnt.attr,
> diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
> index 66d42ed..545408d 100644
> --- a/include/scsi/scsi.h
> +++ b/include/scsi/scsi.h
> @@ -16,6 +16,7 @@ struct scsi_cmnd;
>  
>  enum scsi_timeouts {
>  	SCSI_DEFAULT_EH_TIMEOUT		= 10 * HZ,
> +	SCSI_DEFAULT_RETRY_TIMEOUT	= 0,	/* disabled by default */
>  };
>  
>  /*
> diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
> index d65fbec..04fc5ee 100644
> --- a/include/scsi/scsi_device.h
> +++ b/include/scsi/scsi_device.h
> @@ -121,6 +121,7 @@ struct scsi_device {
>  				 * pass settings from slave_alloc to scsi
>  				 * core. */
>  	unsigned int eh_timeout; /* Error handling timeout */
> +	unsigned int retry_timeout;	/* Command retry timeout */
>  	unsigned writeable:1;
>  	unsigned removable:1;
>  	unsigned changed:1;	/* Data invalid due to media change */


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