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time: Fix overflow when HZ is smaller than 60

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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>
This commit is contained in:
Mikulas Patocka 2014-01-24 16:41:36 -05:00 committed by Thomas Gleixner
parent 38dbfb59d1
commit 80d767d770
1 changed files with 6 additions and 0 deletions
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6
kernel/time/jiffies.c
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@ -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)
{