[REVIEW PATCH] scsi: Add 'retry_timeout' to avoid infinite command retry

[Eiichi Tsukata]

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.

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.

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 */
-- 
1.8.3.1

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