[PATCH 3.16 031/134] scsi: scsi_error: count medium access timeout only once per EH run

[Ben Hutchings]

3.16.47-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Hannes Reinecke <hare@xxxxxxx>

commit 7a38dc0bfb4cc39ed57e120e2224673f3d4d200f upstream.

The current medium access timeout counter will be increased for
each command, so if there are enough failed commands we'll hit
the medium access timeout for even a single device failure and
the following kernel message is displayed:

sd H:C:T:L: [sdXY] Medium access timeout failure. Offlining disk!

Fix this by making the timeout per EH run, ie the counter will
only be increased once per device and EH run.

Fixes: 18a4d0a ("[SCSI] Handle disk devices which can not process medium access commands")
Cc: Ewan Milne <emilne@xxxxxxxxxx>
Cc: Lawrence Obermann <loberman@xxxxxxxxxx>
Cc: Benjamin Block <bblock@xxxxxxxxxxxxxxxxxx>
Cc: Steffen Maier <maier@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
[bwh: Backported to 3.16:
 - Open-code blk_rq_is_passthrough()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/scsi/scsi_error.c  | 18 ++++++++++++++++++
 drivers/scsi/sd.c          | 27 ++++++++++++++++++++++++++-
 drivers/scsi/sd.h          |  1 +
 include/scsi/scsi_driver.h |  1 +
 4 files changed, 46 insertions(+), 1 deletion(-)

--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -224,6 +224,23 @@ scsi_abort_command(struct scsi_cmnd *scm
 }
 
 /**
+ * scsi_eh_reset - call into ->eh_action to reset internal counters
+ * @scmd:	scmd to run eh on.
+ *
+ * The scsi driver might be carrying internal state about the
+ * devices, so we need to call into the driver to reset the
+ * internal state once the error handler is started.
+ */
+static void scsi_eh_reset(struct scsi_cmnd *scmd)
+{
+	if (scmd->request->cmd_type == REQ_TYPE_FS) {
+		struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);
+		if (sdrv->eh_reset)
+			sdrv->eh_reset(scmd);
+	}
+}
+
+/**
  * scsi_eh_scmd_add - add scsi cmd to error handling.
  * @scmd:	scmd to run eh on.
  * @eh_flag:	optional SCSI_EH flag.
@@ -252,6 +269,7 @@ int scsi_eh_scmd_add(struct scsi_cmnd *s
 	if (scmd->eh_eflags & SCSI_EH_ABORT_SCHEDULED)
 		eh_flag &= ~SCSI_EH_CANCEL_CMD;
 	scmd->eh_eflags |= eh_flag;
+	scsi_eh_reset(scmd);
 	list_add_tail(&scmd->eh_entry, &shost->eh_cmd_q);
 	shost->host_failed++;
 	scsi_eh_wakeup(shost);
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -112,6 +112,7 @@ static void sd_rescan(struct device *);
 static int sd_init_command(struct scsi_cmnd *SCpnt);
 static void sd_uninit_command(struct scsi_cmnd *SCpnt);
 static int sd_done(struct scsi_cmnd *);
+static void sd_eh_reset(struct scsi_cmnd *);
 static int sd_eh_action(struct scsi_cmnd *, int);
 static void sd_read_capacity(struct scsi_disk *sdkp, unsigned char *buffer);
 static void scsi_disk_release(struct device *cdev);
@@ -509,6 +510,7 @@ static struct scsi_driver sd_template =
 	.uninit_command		= sd_uninit_command,
 	.done			= sd_done,
 	.eh_action		= sd_eh_action,
+	.eh_reset		= sd_eh_reset,
 };
 
 /*
@@ -1536,6 +1538,26 @@ static const struct block_device_operati
 };
 
 /**
+ *	sd_eh_reset - reset error handling callback
+ *	@scmd:		sd-issued command that has failed
+ *
+ *	This function is called by the SCSI midlayer before starting
+ *	SCSI EH. When counting medium access failures we have to be
+ *	careful to register it only only once per device and SCSI EH run;
+ *	there might be several timed out commands which will cause the
+ *	'max_medium_access_timeouts' counter to trigger after the first
+ *	SCSI EH run already and set the device to offline.
+ *	So this function resets the internal counter before starting SCSI EH.
+ **/
+static void sd_eh_reset(struct scsi_cmnd *scmd)
+{
+	struct scsi_disk *sdkp = scsi_disk(scmd->request->rq_disk);
+
+	/* New SCSI EH run, reset gate variable */
+	sdkp->ignore_medium_access_errors = false;
+}
+
+/**
  *	sd_eh_action - error handling callback
  *	@scmd:		sd-issued command that has failed
  *	@eh_disp:	The recovery disposition suggested by the midlayer
@@ -1564,7 +1586,10 @@ static int sd_eh_action(struct scsi_cmnd
 	 * process of recovering or has it suffered an internal failure
 	 * that prevents access to the storage medium.
 	 */
-	sdkp->medium_access_timed_out++;
+	if (!sdkp->ignore_medium_access_errors) {
+		sdkp->medium_access_timed_out++;
+		sdkp->ignore_medium_access_errors = true;
+	}
 
 	/*
 	 * If the device keeps failing read/write commands but TEST UNIT
--- a/drivers/scsi/sd.h
+++ b/drivers/scsi/sd.h
@@ -90,6 +90,7 @@ struct scsi_disk {
 	unsigned	lbpvpd : 1;
 	unsigned	ws10 : 1;
 	unsigned	ws16 : 1;
+	unsigned	ignore_medium_access_errors : 1;
 };
 #define to_scsi_disk(obj) container_of(obj,struct scsi_disk,dev)
 
--- a/include/scsi/scsi_driver.h
+++ b/include/scsi/scsi_driver.h
@@ -17,6 +17,7 @@ struct scsi_driver {
 	void (*uninit_command)(struct scsi_cmnd *);
 	int (*done)(struct scsi_cmnd *);
 	int (*eh_action)(struct scsi_cmnd *, int);
+	void (*eh_reset)(struct scsi_cmnd *);
 };
 #define to_scsi_driver(drv) \
 	container_of((drv), struct scsi_driver, gendrv)