[SCSI] sym53c8xx: fixes two bugs related to chip reset

This patch fixes two bugs pointed by James Bottomley:

 1. the if (!sym_data->io_reset).  That variable is only ever filled
    by a stack based completion.  If we find it non empty it means
    this code has been entered twice and we have a severe problem,
    so that should just become a BUG_ON(sym_data->io_reset).
 2. sym_data->io_reset should be set to NULL before the routine is
    exited otherwise the PCI recovery code could end up completing
    what will be a bogus pointer into the stack.

Big thanks to James Bottomley for help with the patch.
Signed-off-by: Krzysztof Helt <krzysztof.h1@w.pl>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/sym53c8xx_2/sym_glue.c

@@ -609,22 +609,24 @@ static int sym_eh_handler(int op, char *opname, struct scsi_cmnd *cmd)
 	 */
 #define WAIT_FOR_PCI_RECOVERY	35
 	if (pci_channel_offline(pdev)) {
-		struct completion *io_reset;
 		int finished_reset = 0;
 		init_completion(&eh_done);
 		spin_lock_irq(shost->host_lock);
 		/* Make sure we didn't race */
 		if (pci_channel_offline(pdev)) {
-			if (!sym_data->io_reset)
+			BUG_ON(sym_data->io_reset);
 			sym_data->io_reset = &eh_done;
-			io_reset = sym_data->io_reset;
 		} else {
 			finished_reset = 1;
 		}
 		spin_unlock_irq(shost->host_lock);
 		if (!finished_reset)
-			finished_reset = wait_for_completion_timeout(io_reset,
+			finished_reset = wait_for_completion_timeout
+						(sym_data->io_reset,
 						WAIT_FOR_PCI_RECOVERY*HZ);
+		spin_lock_irq(shost->host_lock);
+		sym_data->io_reset = NULL;
+		spin_unlock_irq(shost->host_lock);
 		if (!finished_reset)
 			return SCSI_FAILED;
 	}
@@ -1879,7 +1881,6 @@ static void sym2_io_resume(struct pci_dev *pdev)
 	spin_lock_irq(shost->host_lock);
 	if (sym_data->io_reset)
 		complete_all(sym_data->io_reset);
-	sym_data->io_reset = NULL;
 	spin_unlock_irq(shost->host_lock);
 }