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s390/vtime: correct idle time calculation

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Use the ACCESS_ONCE macro for both accesses to idle->sequence in the
loops to calculate the idle time. If only one access uses the macro,
the compiler is free to cache the value for the second access which
can cause endless loops.

Cc: stable@vger.kernel.org # 3.6+
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
2013-10-28 12:15:32 +01:00
parent 7ab64a85e1
commit 4560e7c331
2 changed files with 3 additions and 3 deletions
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arch/s390/kernel/vtime.c
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@@ -191,7 +191,7 @@ cputime64_t s390_get_idle_time(int cpu)
sequence = ACCESS_ONCE(idle->sequence);
idle_enter = ACCESS_ONCE(idle->clock_idle_enter);
idle_exit = ACCESS_ONCE(idle->clock_idle_exit);
} while ((sequence & 1) || (idle->sequence != sequence));
} while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence));
return idle_enter ? ((idle_exit ?: now) - idle_enter) : 0;
}