[SCSI] st: retry enlarge_buffer allocation

Make enlarge_buffer() retry allocation if the previously chosen page
order was too small. Really limit the page order to 6. Return error if
the maximum order is not large enough for the request.
Signed-off-by: NKai Makisara <Kai.Makisara@kolumbus.fi>
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/st.c

@@ -3695,6 +3695,8 @@ static struct st_buffer *new_tape_buffer(int need_dma, int max_sg)
 
 
 /* Try to allocate enough space in the tape buffer */
+#define ST_MAX_ORDER 6
+
 static int enlarge_buffer(struct st_buffer * STbuffer, int new_size, int need_dma)
 {
 	int segs, nbr, max_segs, b_size, order, got;
@@ -3723,9 +3725,16 @@ static int enlarge_buffer(struct st_buffer * STbuffer, int new_size, int need_dm
 		b_size = PAGE_SIZE << order;
 	} else {
 		for (b_size = PAGE_SIZE, order = 0;
-		     order <= 6 && b_size < new_size; order++, b_size *= 2)
+		     order < ST_MAX_ORDER && b_size < new_size;
+		     order++, b_size *= 2)
 			;  /* empty */
 	}
+	if (max_segs * (PAGE_SIZE << order) < new_size) {
+		if (order == ST_MAX_ORDER)
+			return 0;
+		normalize_buffer(STbuffer);
+		return enlarge_buffer(STbuffer, new_size, need_dma);
+	}
 
 	for (segs = STbuffer->frp_segs, got = STbuffer->buffer_size;
 	     segs < max_segs && got < new_size;) {