[PATCH] Prevent NULL pointer deref in grab_swap_token

[Dean Roe <roe@sgi.com>]

grab_swap_token() assumes that the current process has an mm struct,
which is not true for kernel threads invoking get_user_pages().  Since
this should be extremely rare, just return from grab_swap_token()
without doing anything.

	Signed-off-by: Dean Roe <roe@sgi.com>


Index: linux-2.6/mm/thrash.c
===================================================================
--- linux-2.6.orig/mm/thrash.c
+++ linux-2.6/mm/thrash.c
@@ -54,6 +54,9 @@
 	struct mm_struct *mm;
 	int reason;
 
+	if (current->mm == NULL)
+		return;
+
 	/* We have the token. Let others know we still need it. */
 	if (has_swap_token(current->mm)) {
 		current->mm->recent_pagein = 1;