From: Paul Mackerras When taking a cpu offline, once the cpu has been removed from cpu_online_map, it is not supposed to service any more interrupts. This presents a problem on ppc64 because we cannot truly disable the decrementer. There used to be cpu_is_offline() checks in several scheduler functions (e.g. rebalance_tick()) which papered over this issue, but these checks were removed recently. So with recent 2.6 kernels, an attempt to offline a cpu can result in a crash in find_busiest_group(). This patch prevents such crashes. Signed-off-by: Nathan Lynch Signed-off-by: Paul Mackerras Signed-off-by: Andrew Morton --- 25-akpm/arch/ppc64/kernel/time.c | 15 ++++++++++++++- 1 files changed, 14 insertions(+), 1 deletion(-) diff -puN arch/ppc64/kernel/time.c~ppc64-dont-call-scheduler-on-offline-cpu arch/ppc64/kernel/time.c --- 25/arch/ppc64/kernel/time.c~ppc64-dont-call-scheduler-on-offline-cpu Tue Aug 17 14:51:28 2004 +++ 25-akpm/arch/ppc64/kernel/time.c Tue Aug 17 14:51:28 2004 @@ -48,6 +48,7 @@ #include #include #include +#include #include #include @@ -245,8 +246,20 @@ int timer_interrupt(struct pt_regs * reg while (lpaca->next_jiffy_update_tb <= (cur_tb = get_tb())) { #ifdef CONFIG_SMP - smp_local_timer_interrupt(regs); + /* + * We cannot disable the decrementer, so in the period + * between this cpu's being marked offline in cpu_online_map + * and calling stop-self, it is taking timer interrupts. + * Avoid calling into the scheduler rebalancing code if this + * is the case. + */ + if (!cpu_is_offline(cpu)) + smp_local_timer_interrupt(regs); #endif + /* + * No need to check whether cpu is offline here; boot_cpuid + * should have been fixed up by now. + */ if (cpu == boot_cpuid) { write_seqlock(&xtime_lock); tb_last_stamp = lpaca->next_jiffy_update_tb; _