ncr5380: Call scsi_eh_prep_cmnd() and scsi_eh_restore_cmnd() as and when appropriate

This bug causes the wrong command to have its sense pointer overwritten,
which sometimes leads to a NULL pointer deref. Fix this by checking which
command is being requeued before restoring the scsi_eh_save data.

It turns out that some targets will disconnect a REQUEST SENSE command.
The autosense algorithm doesn't anticipate this. Hence multiple commands
can end up undergoing autosense simultaneously, and they will all try to
use the same scsi_eh_save struct, which won't work. Defer autosense when
the scsi_eh_save storage is in use by another command.

Fixes: f27db8eb98a1 ("ncr5380: Fix autosense bugs")
Reported-and-tested-by: Michael Schmitz <schmitzmic@gmail.com>
Cc: <stable@vger.kernel.org> # 4.5
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/NCR5380.c

@@ -760,7 +760,7 @@ static struct scsi_cmnd *dequeue_next_cmd(struct Scsi_Host *instance)
 	struct NCR5380_cmd *ncmd;
 	struct scsi_cmnd *cmd;
 
-	if (list_empty(&hostdata->autosense)) {
+	if (hostdata->sensing || list_empty(&hostdata->autosense)) {
 		list_for_each_entry(ncmd, &hostdata->unissued, list) {
 			cmd = NCR5380_to_scmd(ncmd);
 			dsprintk(NDEBUG_QUEUES, instance, "dequeue: cmd=%p target=%d busy=0x%02x lun=%llu\n",
@@ -793,7 +793,7 @@ static void requeue_cmd(struct Scsi_Host *instance, struct scsi_cmnd *cmd)
 	struct NCR5380_hostdata *hostdata = shost_priv(instance);
 	struct NCR5380_cmd *ncmd = scsi_cmd_priv(cmd);
 
-	if (hostdata->sensing) {
+	if (hostdata->sensing == cmd) {
 		scsi_eh_restore_cmnd(cmd, &hostdata->ses);
 		list_add(&ncmd->list, &hostdata->autosense);
 		hostdata->sensing = NULL;

drivers/scsi/atari_NCR5380.c

@@ -862,7 +862,7 @@ static struct scsi_cmnd *dequeue_next_cmd(struct Scsi_Host *instance)
 	struct NCR5380_cmd *ncmd;
 	struct scsi_cmnd *cmd;
 
-	if (list_empty(&hostdata->autosense)) {
+	if (hostdata->sensing || list_empty(&hostdata->autosense)) {
 		list_for_each_entry(ncmd, &hostdata->unissued, list) {
 			cmd = NCR5380_to_scmd(ncmd);
 			dsprintk(NDEBUG_QUEUES, instance, "dequeue: cmd=%p target=%d busy=0x%02x lun=%llu\n",
@@ -901,7 +901,7 @@ static void requeue_cmd(struct Scsi_Host *instance, struct scsi_cmnd *cmd)
 	struct NCR5380_hostdata *hostdata = shost_priv(instance);
 	struct NCR5380_cmd *ncmd = scsi_cmd_priv(cmd);
 
-	if (hostdata->sensing) {
+	if (hostdata->sensing == cmd) {
 		scsi_eh_restore_cmnd(cmd, &hostdata->ses);
 		list_add(&ncmd->list, &hostdata->autosense);
 		hostdata->sensing = NULL;