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Subject: Re: 2.6.13-rc3-mm3
From: Richard Purdie <rpurdie@rpsys.net>
To: Christoph Lameter <christoph@lameter.com>
Cc: Andrew Morton <akpm@osdl.org>, nickpiggin@yahoo.com.au,
       linux-kernel@vger.kernel.org
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Date: Mon, 08 Aug 2005 23:12:31 +0100
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I've done a bit of analysis:

cmpxchg fail fault mm=c3945b20 vma=c304ad84 addr=402cb000 write=2048
ptep=c2af5b2c pmd=c2bc5008 entry=886c0f7 new=886c077 current=886c077

Note the Dirty bit is set on entry and not new where it probably should
be...

  ptep_cmpxchg(mm, address, pte, entry, new_entry)

This will compare "current"(886c077) with "entry"(886c0f7) which are not
equal and the whole thing therefore correctly fails leading to the loop.

The following patch (against -mm) cleared the problem up but I'm not
sure how correct it is:

Index: linux-2.6.12/mm/memory.c
===================================================================
--- linux-2.6.12.orig/mm/memory.c	2005-08-08 23:03:45.000000000 +0100
+++ linux-2.6.12/mm/memory.c	2005-08-08 23:04:02.000000000 +0100
@@ -2046,7 +2046,7 @@
 			return do_wp_page(mm, vma, address, pte, pmd, entry);
 #endif
 		}
-		entry = pte_mkdirty(entry);
+		new_entry = pte_mkdirty(entry);
 	}
 
 	/*