time: Fix overflow when HZ is smaller than 60

When compiling for the IA-64 ski emulator, HZ is set to 32 because the
emulation is slow and we don't want to waste too many cycles processing
timers. Alpha also has an option to set HZ to 32.

This causes integer underflow in
kernel/time/jiffies.c:
kernel/time/jiffies.c:66:2: warning: large integer implicitly truncated to unsigned type [-Woverflow]
  .mult  = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
  ^

This patch reduces the JIFFIES_SHIFT value to avoid the overflow.

Signed-off-by: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1401241639100.23871@file01.intranet.prod.int.rdu2.redhat.com
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index 7a925ba456fb5d617d19b98daf2ca39356c4eca6..a6a5bf53e86d25575f90518399407a4fb65a85ed 100644 (file)
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -51,7 +51,13 @@
  * HZ shrinks, so values greater than 8 overflow 32bits when
  * HZ=100.
  */
+#if HZ < 34
+#define JIFFIES_SHIFT  6
+#elif HZ < 67
+#define JIFFIES_SHIFT  7
+#else
 #define JIFFIES_SHIFT  8
+#endif
 
 static cycle_t jiffies_read(struct clocksource *cs)
 {