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authorRichard Mortimer <richm@oldelvet.org.uk>2006-01-17 15:23:00 -0800
committerGreg Kroah-Hartman <gregkh@suse.de>2006-01-30 22:13:17 -0800
commitd93f4eb4134d693be834627d31cd7c4aac427911 (patch)
treebd1d8b9ea03ff8dd4094d5f4b1693717db4195bb
parent4f3bfdc30b23e63d9c215e47192f427c2d7d4774 (diff)
downloadlinux-linaro-stable-d93f4eb4134d693be834627d31cd7c4aac427911.tar.gz
[PATCH] Fix timekeeping on sparc64 ultra-IIe machines
[SPARC64]: Eliminate race condition reading Hummingbird STICK register Ensure a consistent value is read from the STICK register by ensuring that both high and low are read without high changing due to a roll over of the low register. Various Debian/SPARC users (myself include) have noticed problems with Hummingbird based systems. The symptoms are that the system time is seen to jump forward 3 days, 6 hours, 11 minutes give or take a few seconds. In many cases the system then hangs some time afterwards. I've spotted a race condition in the code to read the STICK register. I could not work out why 3d, 6h, 11m is important but guess that it is due to the 2^32 jump of STICK (forwards on one read and then the next read will seem to be backwards) during a timer interrupt. I'm guessing that a change of -2^32 will get converted to a large unsigned increment after the arithmetic manipulation between STICK, nanoseconds, jiffies etc. I did a test where I modified __hbird_read_stick to artificially inject rollover faults forcefully every few seconds. With this I saw the clock jump over 6 times in 12 hours compared to once every month or so. Signed-off-by: Richard Mortimer <richm@oldelvet.org.uk> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Chris Wright <chrisw@sous-sol.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--arch/sparc64/kernel/time.c22
1 files changed, 11 insertions, 11 deletions
diff --git a/arch/sparc64/kernel/time.c b/arch/sparc64/kernel/time.c
index 459c8fbe02b4..a22930d62adf 100644
--- a/arch/sparc64/kernel/time.c
+++ b/arch/sparc64/kernel/time.c
@@ -280,9 +280,9 @@ static struct sparc64_tick_ops stick_operations __read_mostly = {
* Since STICK is constantly updating, we have to access it carefully.
*
* The sequence we use to read is:
- * 1) read low
- * 2) read high
- * 3) read low again, if it rolled over increment high by 1
+ * 1) read high
+ * 2) read low
+ * 3) read high again, if it rolled re-read both low and high again.
*
* Writing STICK safely is also tricky:
* 1) write low to zero
@@ -295,18 +295,18 @@ static struct sparc64_tick_ops stick_operations __read_mostly = {
static unsigned long __hbird_read_stick(void)
{
unsigned long ret, tmp1, tmp2, tmp3;
- unsigned long addr = HBIRD_STICK_ADDR;
+ unsigned long addr = HBIRD_STICK_ADDR+8;
- __asm__ __volatile__("ldxa [%1] %5, %2\n\t"
- "add %1, 0x8, %1\n\t"
- "ldxa [%1] %5, %3\n\t"
+ __asm__ __volatile__("ldxa [%1] %5, %2\n"
+ "1:\n\t"
"sub %1, 0x8, %1\n\t"
+ "ldxa [%1] %5, %3\n\t"
+ "add %1, 0x8, %1\n\t"
"ldxa [%1] %5, %4\n\t"
"cmp %4, %2\n\t"
- "blu,a,pn %%xcc, 1f\n\t"
- " add %3, 1, %3\n"
- "1:\n\t"
- "sllx %3, 32, %3\n\t"
+ "bne,a,pn %%xcc, 1b\n\t"
+ " mov %4, %2\n\t"
+ "sllx %4, 32, %4\n\t"
"or %3, %4, %0\n\t"
: "=&r" (ret), "=&r" (addr),
"=&r" (tmp1), "=&r" (tmp2), "=&r" (tmp3)