diff options
authorHeiko Carstens <heiko.carstens@de.ibm.com>2013-01-29 09:16:28 +0100
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2013-01-31 14:01:52 +0100
commitd911e03d097bdc01363df5d81c43f69432eb785c (patch)
parent04c2eee5b9dfcb13f3cd07a5537fb8c785f2751a (diff)
s390/timer: avoid overflow when programming clock comparator
Since ed4f209 "s390/time: fix sched_clock() overflow" a new helper function is used to avoid overflows when converting TOD format values to nanosecond values. The kvm interrupt code formerly however only worked by accident because of an overflow. It tried to program a timer that would expire in more than ~29 years. Because of the old TOD-to-nanoseconds overflow bug the real expiry value however was much smaller, but now it isn't anymore. This however triggers yet another bug in the function that programs the clock comparator s390_next_ktime(): if the absolute "expires" value is after 2042 this will result in an overflow and the programmed value is lower than the current TOD value which immediatly triggers a clock comparator (= timer) interrupt. Since the timer isn't expired it will be programmed immediately again and so on... the result is a dead system. To fix this simply program the maximum possible value if an overflow is detected. Reported-by: Christian Borntraeger <borntraeger@de.ibm.com> Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> Cc: stable@vger.kernel.org # v3.3+ Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index a5f4f5a1d24..0aa98db8a80 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -120,6 +120,9 @@ static int s390_next_ktime(ktime_t expires,
nsecs = ktime_to_ns(ktime_add(timespec_to_ktime(ts), expires));
do_div(nsecs, 125);
S390_lowcore.clock_comparator = sched_clock_base_cc + (nsecs << 9);
+ /* Program the maximum value if we have an overflow (== year 2042) */
+ if (unlikely(S390_lowcore.clock_comparator < sched_clock_base_cc))
+ S390_lowcore.clock_comparator = -1ULL;
return 0;