On Sat, 2013-04-27 at 15:40 +0200, Frederic Weisbecker wrote: > 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.
OK, I'll send an updated version, using local_irq_save() to protect it. I tried using raw_* because seems it could avoid some unnecessary irq disabling... Thanks, Zhong > 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/
