time: prevent the loop in timespec_add_ns() from being optimised away

[Chris Wright]

-stable review patch.  If anyone has any objections, please let us know.
---------------------

From: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>

upstream commit: 38332cb98772f5ea757e6486bed7ed0381cb5f98

Since some architectures don't support __udivdi3().

Signed-off-by: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>
Cc: john stultz <johnstul@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc:  Sedat Dilek <sedat.dilek@xxxxxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
---
 include/linux/time.h |    4 ++++
 1 file changed, 4 insertions(+)

--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -173,6 +173,10 @@ static inline void timespec_add_ns(struc
 {
 	ns += a->tv_nsec;
 	while(unlikely(ns >= NSEC_PER_SEC)) {
+		/* The following asm() prevents the compiler from
+		 * optimising this loop into a modulo operation.  */
+		asm("" : "+r"(ns));
+
 		ns -= NSEC_PER_SEC;
 		a->tv_sec++;
 	}

-- 
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