Messages in this thread | | | Subject | Re: [RFC PATCH]nohz: Use raw_smp_processor_id() in tick_nohz_task_switch() | From | Li Zhong <> | Date | Sun, 28 Apr 2013 09:56:49 +0800 |
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On Sat, 2013-04-27 at 15:40 +0200, Frederic Weisbecker wrote: > 2013/4/27 Li Zhong <zhong@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! >
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