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Subject[PATCH REPOST for 2.6.25] Use an own random generator for pageattr-test.c
Use an own random generator for pageattr-test.c

[Repost. Please ack/nack. This is a bug fix and imho a .25 late merge
candidate because it fixes a subtle bug]

pageattr-test attempts to be repeatable and uses srandom32 to get a
repeatable random number sequence.

Using srandom32() wasn't a good idea for various reasons:
- it is per cpu and if the cpu changes on a preemptible kernel it gets lost
- networking and random32 puts in some own state
- srandom32() does not actually reset the state, but just adds bits to
it

Instead use a very simple private standard rnd that gives repeatable
results. I took the reference rand() from ISO-C.

Signed-off-by: Andi Kleen <ak@suse.de>

---
arch/x86/mm/pageattr-test.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

Index: linux/arch/x86/mm/pageattr-test.c
===================================================================
--- linux.orig/arch/x86/mm/pageattr-test.c
+++ linux/arch/x86/mm/pageattr-test.c
@@ -101,6 +101,14 @@ static int print_split(struct split_stat
static unsigned long addr[NTEST];
static unsigned int len[NTEST];

+static int next = 100;
+
+static unsigned my_rand(void)
+{
+ next = next * 1103515245 + 12345;
+ return next;
+}
+
/* Change the global bit on random pages in the direct mapping */
static int pageattr_test(void)
{
@@ -123,10 +131,9 @@ static int pageattr_test(void)
memset(bm, 0, (max_pfn_mapped + 7) / 8);

failed += print_split(&sa);
- srandom32(100);

for (i = 0; i < NTEST; i++) {
- unsigned long pfn = random32() % max_pfn_mapped;
+ unsigned long pfn = my_rand() % max_pfn_mapped;

addr[i] = (unsigned long)__va(pfn << PAGE_SHIFT);
len[i] = random32() % 100;

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