2013/4/27 Li Zhong <zh...@linux.vnet.ibm.com>: > 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.
You're right it looks safe to do so. But I suggest we rather move the test inside local_irq_save()/restore section to avoid confusion on reviewers minds. Thanks! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
