[PATCHv4 1/8] scsi_error: count medium access timeout only once per EH run

Hannes Reinecke
2017-04-04T14:03:11Z

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@redhat.com>
Cc: Lawrence Obermann <loberman@redhat.com>
Cc: Benjamin Block <bblock@linux.vnet.ibm.com>
Cc: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: Hannes Reinecke <hare@suse.com>
---
drivers/scsi/scsi_error.c | 23 ++++++++++++++++++++++-
drivers/scsi/sd.c | 22 ++++++++++++++++++----
drivers/scsi/sd.h | 1 +
include/scsi/scsi_driver.h | 2 +-
4 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index f2cafae..390a6bc 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -221,6 +221,26 @@ static int scsi_host_eh_past_deadline(struct Scsi_Host *shost)
}

/**
+ * 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 int scsi_eh_reset(struct scsi_cmnd *scmd)
+{
+ int rtn = SUCCESS;
+
+ if (!blk_rq_is_passthrough(scmd->request)) {
+ struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);
+ if (sdrv->eh_action)
+ rtn = sdrv->eh_action(scmd, rtn, true);
+ }
+ return rtn;
+}
+
+/**
* scsi_eh_scmd_add - add scsi cmd to error handling.
* @scmd: scmd to run eh on.
* @eh_flag: optional SCSI_EH flag.
@@ -249,6 +269,7 @@ int scsi_eh_scmd_add(struct scsi_cmnd *scmd, int eh_flag)
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);
@@ -1107,7 +1128,7 @@ static int scsi_eh_action(struct scsi_cmnd *scmd, int rtn)
if (!blk_rq_is_passthrough(scmd->request)) {
struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);
if (sdrv->eh_action)
- rtn = sdrv->eh_action(scmd, rtn);
+ rtn = sdrv->eh_action(scmd, rtn, false);
}
return rtn;
}
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index d277e86..656a32d 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -115,7 +115,7 @@
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 int sd_eh_action(struct scsi_cmnd *, int);
+static int sd_eh_action(struct scsi_cmnd *, int, bool);
static void sd_read_capacity(struct scsi_disk *sdkp, unsigned char *buffer);
static void scsi_disk_release(struct device *cdev);
static void sd_print_sense_hdr(struct scsi_disk *, struct scsi_sense_hdr *);
@@ -1689,18 +1689,29 @@ static int sd_pr_clear(struct block_device *bdev, u64 key)
* sd_eh_action - error handling callback
* @scmd: sd-issued command that has failed
* @eh_disp: The recovery disposition suggested by the midlayer
+ * @restart: SCSI EH has been restarted
*
* This function is called by the SCSI midlayer upon completion of an
* error test command (currently TEST UNIT READY). The result of sending
* the eh command is passed in eh_disp. We're looking for devices that
* fail medium access commands but are OK with non access commands like
* test unit ready (so wrongly see the device as having a successful
- * recovery)
+ * recovery).
+ * We have to be careful to count a medium access failure 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.
**/
-static int sd_eh_action(struct scsi_cmnd *scmd, int eh_disp)
+static int sd_eh_action(struct scsi_cmnd *scmd, int eh_disp, bool restart)
{
struct scsi_disk *sdkp = scsi_disk(scmd->request->rq_disk);

+ if (restart) {
+ /* New SCSI EH run, reset gate variable */
+ sdkp->ignore_medium_access_errors = false;
+ return eh_disp;
+ }
if (!scsi_device_online(scmd->device) ||
!scsi_medium_access_command(scmd) ||
host_byte(scmd->result) != DID_TIME_OUT ||
@@ -1714,7 +1725,10 @@ static int sd_eh_action(struct scsi_cmnd *scmd, int eh_disp)
* 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
diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
index 4dac35e..0cf9680 100644
--- a/drivers/scsi/sd.h
+++ b/drivers/scsi/sd.h
@@ -106,6 +106,7 @@ struct scsi_disk {
unsigned rc_basis: 2;
unsigned zoned: 2;
unsigned urswrz : 1;
+ unsigned ignore_medium_access_errors : 1;
};
#define to_scsi_disk(obj) container_of(obj,struct scsi_disk,dev)

diff --git a/include/scsi/scsi_driver.h b/include/scsi/scsi_driver.h
index 891a658..d5e0012 100644
--- a/include/scsi/scsi_driver.h
+++ b/include/scsi/scsi_driver.h
@@ -15,7 +15,7 @@ struct scsi_driver {
int (*init_command)(struct scsi_cmnd *);
void (*uninit_command)(struct scsi_cmnd *);
int (*done)(struct scsi_cmnd *);
- int (*eh_action)(struct scsi_cmnd *, int);
+ int (*eh_action)(struct scsi_cmnd *, int, bool);
};
#define to_scsi_driver(drv) \
container_of((drv), struct scsi_driver, gendrv)
--
1.8.5.6