diff --git a/arch/ia64/sn/kernel/mca.c b/arch/ia64/sn/kernel/mca.c
index 857774b..6546db6 100644
--- a/arch/ia64/sn/kernel/mca.c
+++ b/arch/ia64/sn/kernel/mca.c
@@ -37,6 +37,11 @@
  * This function is the callback routine that SAL calls to log error
  * info for platform errors.  buf is appended to sn_oemdata, resizing as
  * required.
+ * Note: this is a SAL to OS callback, running under the same rules as the SAL
+ * code.  SAL calls are run with preempt disabled so this routine must not
+ * sleep.  vmalloc can sleep so print_hook cannot resize the output buffer
+ * itself, instead it must set the required size and return to let the caller
+ * resize the buffer then redrive the SAL call.
  */
 static int print_hook(const char *fmt, ...)
 {
@@ -47,18 +52,8 @@
 	vsnprintf(buf, sizeof(buf), fmt, args);
 	va_end(args);
 	len = strlen(buf);
-	while (*sn_oemdata_size + len + 1 > sn_oemdata_bufsize) {
-		u8 *newbuf = vmalloc(sn_oemdata_bufsize += 1000);
-		if (!newbuf) {
-			printk(KERN_ERR "%s: unable to extend sn_oemdata\n",
-			       __FUNCTION__);
-			return 0;
-		}
-		memcpy(newbuf, *sn_oemdata, *sn_oemdata_size);
-		vfree(*sn_oemdata);
-		*sn_oemdata = newbuf;
-	}
-	memcpy(*sn_oemdata + *sn_oemdata_size, buf, len + 1);
+	if (*sn_oemdata_size + len <= sn_oemdata_bufsize)
+		memcpy(*sn_oemdata + *sn_oemdata_size, buf, len);
 	*sn_oemdata_size += len;
 	return 0;
 }
@@ -98,7 +93,20 @@
 	sn_oemdata = oemdata;
 	sn_oemdata_size = oemdata_size;
 	sn_oemdata_bufsize = 0;
-	ia64_sn_plat_specific_err_print(print_hook, (char *)sect_header);
+	*sn_oemdata_size = PAGE_SIZE;	/* first guess at how much data will be generated */
+	while (*sn_oemdata_size > sn_oemdata_bufsize) {
+		u8 *newbuf = vmalloc(*sn_oemdata_size);
+		if (!newbuf) {
+			printk(KERN_ERR "%s: unable to extend sn_oemdata\n",
+			       __FUNCTION__);
+			return 1;
+		}
+		vfree(*sn_oemdata);
+		*sn_oemdata = newbuf;
+		sn_oemdata_bufsize = *sn_oemdata_size;
+		*sn_oemdata_size = 0;
+		ia64_sn_plat_specific_err_print(print_hook, (char *)sect_header);
+	}
 	up(&sn_oemdata_mutex);
 	return 0;
 }