s390/timer: avoid overflow when programming clock comparator
authorHeiko Carstens <heiko.carstens@de.ibm.com>
Tue, 29 Jan 2013 08:16:28 +0000 (09:16 +0100)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sun, 17 Feb 2013 18:53:12 +0000 (10:53 -0800)
commit250d9091312fc96986d3a6ba2c44e14fee546231
tree52711ff27599eda438ed07c43e17c2a7bb0aefea
parent422224746ba5bf508e66b6f4e2cd18ad878a4637
s390/timer: avoid overflow when programming clock comparator

commit d911e03d097bdc01363df5d81c43f69432eb785c upstream.

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>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/s390/kernel/time.c