Commit 80d767d7 authored Jan 24, 2014 by Mikulas Patocka Committed by Thomas Gleixner Feb 06, 2014

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>

parent 38dbfb59

kernel/time/jiffies.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -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)
		{