[PATCH] s390: fix sclp memory corruption in tty pages list

When the sclp interface takes very long to serve a request, the sclp core
driver will report a failed request to the sclp tty driver even though the
request is still being processed by the sclp interface.  Eventually the sclp
interface completes the request and updates some fields in the request buffer
which leads to a corrupted tty pages list.  The next time function
sclp_tty_write_room is called, the corrupted list will be traversed, resulting
in an oops.

To avoid this remove the busy retry limit and increase retry intervals.

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/s390/char/sclp.c

@@ -85,11 +85,10 @@ static volatile enum sclp_mask_state_t {
 /* Maximum retry counts */
 #define SCLP_INIT_RETRY		3
 #define SCLP_MASK_RETRY		3
-#define SCLP_REQUEST_RETRY	3
 
 /* Timeout intervals in seconds.*/
-#define SCLP_BUSY_INTERVAL	2
-#define SCLP_RETRY_INTERVAL	5
+#define SCLP_BUSY_INTERVAL	10
+#define SCLP_RETRY_INTERVAL	15
 
 static void sclp_process_queue(void);
 static int sclp_init_mask(int calculate);
@@ -153,11 +152,9 @@ __sclp_start_request(struct sclp_req *req)
 	if (sclp_running_state != sclp_running_state_idle)
 		return 0;
 	del_timer(&sclp_request_timer);
-	if (req->start_count <= SCLP_REQUEST_RETRY) {
-		rc = service_call(req->command, req->sccb);
-		req->start_count++;
-	} else
-		rc = -EIO;
+	rc = service_call(req->command, req->sccb);
+	req->start_count++;
+
 	if (rc == 0) {
 		/* Sucessfully started request */
 		req->status = SCLP_REQ_RUNNING;