Re: [PATCH] s390: lost dirty bits.

Martin Schwidefsky [off-list ref] wrote:

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 [off-list ref]

 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)

Do you know what the call path for the redundant SetpageUptodate() is?

This patch still has a little race - it'd be better to override _all_ of
SetPageUptodate() in page-flags.h and do:

	if (!test_and_set_bit(PG_uptodate, &page->flags))
		...

--- 25/include/asm-s390/pgtable.h~s390-lost-dirty-bits	2004-06-15 21:02:00.621441504 -0700
+++ 25-akpm/include/asm-s390/pgtable.h	2004-06-15 21:06:43.391453928 -0700

@@ -656,7 +656,8 @@ static inline pte_t mk_pte_phys(unsigned
 
 #define arch_set_page_uptodate(__page)					  \
 	do {								  \
-		asm volatile ("sske %0,%1" : : "d" (0),			  \
+		if (!test_and_set_bit(PG_uptodate, __page))		  \
+			asm volatile ("sske %0,%1" : : "d" (0),		  \
 			      "a" (__pa((__page-mem_map) << PAGE_SHIFT)));\
 	} while (0)
 

diff -puN include/linux/page-flags.h~s390-lost-dirty-bits include/linux/page-flags.h

--- 25/include/linux/page-flags.h~s390-lost-dirty-bits	2004-06-15 21:04:58.982326528 -0700
+++ 25-akpm/include/linux/page-flags.h	2004-06-15 21:08:30.493171992 -0700

@@ -194,16 +194,12 @@ extern unsigned long __read_page_state(u
 #define ClearPageReferenced(page)	clear_bit(PG_referenced, &(page)->flags)
 #define TestClearPageReferenced(page) test_and_clear_bit(PG_referenced, &(page)->flags)
 
-#ifndef arch_set_page_uptodate
-#define arch_set_page_uptodate(page) do { } while (0)
+#ifdef arch_set_page_uptodate
+#define SetPageUptodate(page) arch_set_page_uptodate(page)
+#else
+#define SetPageUptodate(page) set_bit(PG_uptodate, &(page)->flags)
 #endif
-
 #define PageUptodate(page)	test_bit(PG_uptodate, &(page)->flags)
-#define SetPageUptodate(page) \
-	do {								\
-		arch_set_page_uptodate(page);				\
-		set_bit(PG_uptodate, &(page)->flags);			\
-	} while (0)
 #define ClearPageUptodate(page)	clear_bit(PG_uptodate, &(page)->flags)
 
 #define PageDirty(page)		test_bit(PG_dirty, &(page)->flags)

_

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