[PATCH] s390: lost dirty bits.

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

Hi Andrew,
we just tracked down a severe bug in the memory management
code of s390. There is a race window where s390 can loose
a dirty bit. I never expected that SetPageUptodate is called
on an already up to date page...

blue skies,
  Martin.

---

[PATCH] s390: lost dirty bits.

The SetPageUptodate function is called for pages that are already
up to date. The arch_set_page_uptodate function of s390 may not
clear the dirty bit in that case otherwise a dirty bit which is set
between the start of an i/o for a writeback and a following call
to SetPageUptodate is lost.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diffstat:

--- linux-2.5/include/asm-s390/pgtable.h	24 Mar 2004 18:18:22 -0000	1.23
+++ linux-2.5/include/asm-s390/pgtable.h	15 Jun 2004 16:43:35 -0000	1.23.2.1
@@ -652,7 +652,8 @@
 
 #define arch_set_page_uptodate(__page)					  \
 	do {								  \
-		asm volatile ("sske %0,%1" : : "d" (0),			  \
+		if (!PageUptodate(__page))				  \
+			asm volatile ("sske %0,%1" : : "d" (0),		  \
 			      "a" (__pa((__page-mem_map) << PAGE_SHIFT)));\
 	} while (0)
 

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