Messages in this thread | | | Date | Fri, 10 May 2013 17:43:50 +0200 | From | Frederic Weisbecker <> | Subject | Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule |
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On Fri, May 10, 2013 at 05:21:02PM +0200, Borislav Petkov wrote: > On Fri, May 10, 2013 at 05:03:56PM +0200, Jiri Kosina wrote: > > [ ... snip ... ] > > Enabling non-boot CPUs ... > > smpboot: Booting Node 0 Processor 1 APIC 0x1 > > CPU1 microcode updated early to revision 0x60f, date = 2010-09-29 > > Disabled fast string operations > > 1 1 > > CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.9.0-12317-gb2031d4 #1 > > Hardware name: LENOVO 7470BN2/7470BN2, BIOS 6DET38WW (2.02 ) 12/19/2008 > > ffff88007c28cca0 ffff880079851e08 ffffffff8154837e ffff880079851e28 > > ffffffff81077514 ffff88007c28cca0 ffff88007c28cca0 ffff880079851e68 > > ffffffff810529db 0000000179851e78 ffff88007c28cca0 0000000000000001 > > Call Trace: > > [<ffffffff8154837e>] dump_stack+0x19/0x1b > > [<ffffffff81077514>] wake_up_nohz_cpu+0xd4/0xf0 > > [<ffffffff810529db>] add_timer_on+0xdb/0x110 > > [<ffffffff8101e4f4>] mce_start_timer+0x64/0x70 > > [<ffffffff8101e552>] __mcheck_cpu_init_timer+0x52/0x60 > > [<ffffffff8153e22e>] mcheck_cpu_init+0x6f/0x111 > > [<ffffffff8153b94e>] identify_cpu+0x3cc/0x3f9 > > [<ffffffff8153b98d>] identify_secondary_cpu+0x12/0x1d > > [<ffffffff8153fdd6>] smp_store_cpu_info+0x3a/0x3c > > [<ffffffff8153fec2>] smp_callin+0xea/0x1c1 > > [<ffffffff8153ffbd>] start_secondary+0x24/0x97 > > Ok, I got it: > > smp_callin is called by start_secondary() and down that path we add the > timer and do wake_up_nohz_cpu. > > HOWEVER(!), the bit in the cpu_online_mask is set much later in > smp_callin() with > > set_cpu_online(smp_processor_id(), true); > > Thus, when we come to send the IPI, the cpu is still offline, according > to the cpu_online_mask, thus the WARN_ON. > > Nice :-\
Right. But this is adding a timer locally, from CPU 1 to CPU 1, as indicated in the trace with the "1 1" line. So the only way for this IPI to be self-sent is if the tick is stopped locally (cf: wake_up_full_nohz_cpu()).
But the tick is not supposed to be stopped so early in a secondary CPU initialization. The tick can be stopped only from two places:
1) idle loop, but we haven't yet reached that place. cpu_idle() is called much later 2) interrupt exit, but interrupts are supposed to be disabled at this stage
So either interrupts are spuriously enabled early, or ts->tick_stopped is not correctly initialized.
> > -- > Regards/Gruss, > Boris. > > Sent from a fat crate under my desk. Formatting is fine. > --
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