[SCSI] Handle disk devices which can not process medium access commands

We have experienced several devices which fail in a fashion we do not
currently handle gracefully in SCSI. After a failure these devices will
respond to the SCSI primary command set (INQUIRY, TEST UNIT READY, etc.)
but any command accessing the storage medium will time out.

The following patch adds an callback that can be used by upper level
drivers to inspect the results of an error handling command. This in
turn has been used to implement additional checking in the SCSI disk
driver.

If a medium access command fails twice but TEST UNIT READY succeeds both
times in the subsequent error handling we will offline the device. The
maximum number of failed commands required to take a device offline can
be tweaked in sysfs.

Also add a new error flag to scsi_debug which allows this scenario to be
easily reproduced.

[jejb: fix up integer parsing to use kstrtouint]
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index d2fd0efca565..8917154d96c7 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -126,6 +126,7 @@ static const char * scsi_debug_version_date = "20100324";
 #define SCSI_DEBUG_OPT_TRANSPORT_ERR   16
 #define SCSI_DEBUG_OPT_DIF_ERR   32
 #define SCSI_DEBUG_OPT_DIX_ERR   64
+#define SCSI_DEBUG_OPT_MAC_TIMEOUT  128
 /* When "every_nth" > 0 then modulo "every_nth" commands:
  *   - a no response is simulated if SCSI_DEBUG_OPT_TIMEOUT is set
  *   - a RECOVERED_ERROR is simulated on successful read and write
@@ -3615,6 +3616,9 @@ int scsi_debug_queuecommand_lck(struct scsi_cmnd *SCpnt, done_funct_t done)
                         scsi_debug_every_nth = -1;
                 if (SCSI_DEBUG_OPT_TIMEOUT & scsi_debug_opts)
                         return 0; /* ignore command causing timeout */
+                else if (SCSI_DEBUG_OPT_MAC_TIMEOUT & scsi_debug_opts &&
+                         scsi_medium_access_command(SCpnt))
+                        return 0; /* time out reads and writes */
                 else if (SCSI_DEBUG_OPT_RECOVERED_ERR & scsi_debug_opts)
                         inj_recovered = 1; /* to reads and writes below */
                 else if (SCSI_DEBUG_OPT_TRANSPORT_ERR & scsi_debug_opts)