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Date: Mon, 12 Jun 2006 15:16:35 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
To: Cedric Le Goater <clg@fr.ibm.com>
cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       Christoph Lameter <clameter@engr.sgi.com>
Subject: Re: 2.6.16-rc6-mm2
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On Mon, 12 Jun 2006, Cedric Le Goater wrote:

> Unable to handle kernel NULL pointer dereference at 0000000000000007 RIP:
>  [<ffffffff8025b017>] dec_zone_page_state+0x1/0x5b

Seems that req->wb_page may be NULL.

This patch may fix it but we may miss an unstable page then. We may 
have to move the decrement of NR_UNSTABLE to a different location when
wb_page is still valid.

Index: linux-2.6.17-rc6-cl/fs/nfs/write.c
===================================================================
--- linux-2.6.17-rc6-cl.orig/fs/nfs/write.c	2006-06-12 13:37:47.321243148 -0700
+++ linux-2.6.17-rc6-cl/fs/nfs/write.c	2006-06-12 15:13:48.020908204 -0700
@@ -1419,7 +1419,8 @@ static void nfs_commit_done(struct rpc_t
 		nfs_mark_request_dirty(req);
 	next:
 		nfs_clear_page_writeback(req);
-		dec_zone_page_state(req->wb_page, NR_UNSTABLE);
+		if (req->wb_page)
+			dec_zone_page_state(req->wb_page, NR_UNSTABLE);
 	}
 }