s390/time: correct use of store clock fast

The result of the store-clock-fast (STCKF) instruction is a bit fuzzy.
It can happen that the value stored on one CPU is smaller than the value
stored on another CPU, although the order of the stores is the other
way around. This can cause deltas of get_tod_clock() values to become
negative when they should not be.

We need to be more careful with store-clock-fast, this patch partially
reverts git commit e4b7b4238e666682555461fa52eecd74652f36bb "time:
always use stckf instead of stck if available". The get_tod_clock()
function now uses the store-clock-extended (STCKE) instruction.
get_tod_clock_fast() can be used if the fuzziness of store-clock-fast
is acceptable e.g. for wait loops local to a CPU.

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

1 files changed, 7 insertions, 7 deletions

diff --git a/arch/s390/lib/delay.c b/arch/s390/lib/delay.c
index 57c87d7d7ede..a9f3d0042d58 100644
--- a/arch/s390/lib/delay.c
+++ b/arch/s390/lib/delay.c
@@ -44,7 +44,7 @@ static void __udelay_disabled(unsigned long long usecs)
         do {
                 set_clock_comparator(end);
                 vtime_stop_cpu();
-        } while (get_tod_clock() < end);
+        } while (get_tod_clock_fast() < end);
         lockdep_on();
         __ctl_load(cr0, 0, 0);
         __ctl_load(cr6, 6, 6);
@@ -55,7 +55,7 @@ static void __udelay_enabled(unsigned long long usecs)
 {
         u64 clock_saved, end;
 
-        end = get_tod_clock() + (usecs << 12);
+        end = get_tod_clock_fast() + (usecs << 12);
         do {
                 clock_saved = 0;
                 if (end < S390_lowcore.clock_comparator) {
@@ -65,7 +65,7 @@ static void __udelay_enabled(unsigned long long usecs)
                 vtime_stop_cpu();
                 if (clock_saved)
                         local_tick_enable(clock_saved);
-        } while (get_tod_clock() < end);
+        } while (get_tod_clock_fast() < end);
 }
 
 /*
@@ -109,8 +109,8 @@ void udelay_simple(unsigned long long usecs)
 {
         u64 end;
 
-        end = get_tod_clock() + (usecs << 12);
-        while (get_tod_clock() < end)
+        end = get_tod_clock_fast() + (usecs << 12);
+        while (get_tod_clock_fast() < end)
                 cpu_relax();
 }
 
@@ -120,10 +120,10 @@ void __ndelay(unsigned long long nsecs)
 
         nsecs <<= 9;
         do_div(nsecs, 125);
-        end = get_tod_clock() + nsecs;
+        end = get_tod_clock_fast() + nsecs;
         if (nsecs & ~0xfffUL)
                 __udelay(nsecs >> 12);
-        while (get_tod_clock() < end)
+        while (get_tod_clock_fast() < end)
                 barrier();
 }
 EXPORT_SYMBOL(__ndelay);