I saw following error when testing the latest nohz code on Power: [ 85.295384] BUG: using smp_processor_id() in preemptible [00000000] code: rsyslogd/3493 [ 85.295396] caller is .tick_nohz_task_switch+0x1c/0xb8 [ 85.295402] Call Trace: [ 85.295408] [c0000001fababab0] [c000000000012dc4] .show_stack+0x110/0x25c (unreliable) [ 85.295420] [c0000001fababba0] [c0000000007c4b54] .dump_stack+0x20/0x30 [ 85.295430] [c0000001fababc10] [c00000000044eb74] .debug_smp_processor_id+0xf4/0x124 [ 85.295438] [c0000001fababca0] [c0000000000d7594] .tick_nohz_task_switch+0x1c/0xb8 [ 85.295447] [c0000001fababd20] [c0000000000b9748] .finish_task_switch+0x13c/0x160 [ 85.295455] [c0000001fababdb0] [c0000000000bbe50] .schedule_tail+0x50/0x124 [ 85.295463] [c0000001fababe30] [c000000000009dc8] .ret_from_fork+0x4/0x54
It seems to me that we could just use raw_smp_processor_id() here. Even if the tick_nohz_full_cpu() check is done on a !nohz_full cpu, then the task is moved to another nohz_full cpu, it seems the context switching because of the task moving would call tick_nohz_task_switch() again to evaluate the need for tick. I don't know whether I missed something here. Signed-off-by: Li Zhong <[email protected]> --- kernel/time/tick-sched.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index da53c8f..0aa575b 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -251,7 +251,7 @@ void tick_nohz_task_switch(struct task_struct *tsk) { unsigned long flags; - if (!tick_nohz_full_cpu(smp_processor_id())) + if (!tick_nohz_full_cpu(raw_smp_processor_id())) return; local_irq_save(flags); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
