scsi: atari_scsi: Fix race condition between .queuecommand and EH

It is possible that bus_reset_cleanup() or .eh_abort_handler could be
invoked during NCR5380_queuecommand(). If that takes place before the new
command is enqueued and after the ST-DMA "lock" has been acquired, the
ST-DMA "lock" will be released again. This will result in a lost DMA
interrupt and a command timeout. Fix this by excluding EH and interrupt
handlers while the new command is enqueued.

Link: https://lore.kernel.org/r/[e-mail]
Tested-by: Michael Schmitz <[e-mail]>
Reviewed-by: Michael Schmitz <[e-mail]>
Signed-off-by: Finn Thain <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/NCR5380.c

···
 
 	cmd->result = 0;
 
-	if (!NCR5380_acquire_dma_irq(instance))
-		return SCSI_MLQUEUE_HOST_BUSY;
-
 	spin_lock_irqsave(&hostdata->lock, flags);
+
+	if (!NCR5380_acquire_dma_irq(instance)) {
+		spin_unlock_irqrestore(&hostdata->lock, flags);
+
+		return SCSI_MLQUEUE_HOST_BUSY;
+	}
 
 	/*
 	 * Insert the cmd into the issue queue. Note that REQUEST SENSE

drivers/scsi/atari_scsi.c

···
 	if (IS_A_TT())
 		return 1;
 
-	if (stdma_is_locked_by(scsi_falcon_intr) &&
-	    instance->hostt->can_queue > 1)
+	if (stdma_is_locked_by(scsi_falcon_intr))
 		return 1;
 
-	if (in_interrupt())
-		return stdma_try_lock(scsi_falcon_intr, instance);
-
-	stdma_lock(scsi_falcon_intr, instance);
-	return 1;
+	/* stdma_lock() may sleep which means it can't be used here */
+	return stdma_try_lock(scsi_falcon_intr, instance);
 }
 
 #ifndef MODULE