s390/cputime: fix incorrect system time
git commit c5328901 "[S390] entry[64].S improvements" removed the update of the exit_timer lowcore field from the critical section cleanup of the .Lsysc_restore/.Lsysc_done and .Lio_restore/.Lio_done blocks. If the PSW is updated by the critical section cleanup to point to user space again, the interrupt entry code will do a vtime calculation after the cleanup completed with an exit_timer value which has *not* been updated. Due to this incorrect system time deltas are calculated. If an interrupt occured with an old PSW between .Lsysc_restore/.Lsysc_done or .Lio_restore/.Lio_done update __LC_EXIT_TIMER with the system entry time of the interrupt. Cc: stable@vger.kernel.org # 3.3+ Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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