Re: 2.6-bk: cpu hotplug + preempt = smp_processor_id warnings galore

[Matthias-Christian Ott]

Nathan Lynch wrote:

> Hi-
>
> With 2.6.11-rc3-bk7 on ppc64 I am seeing lots of smp_processor_id
> warnings whenever I hotplug cpus:
>
> # echo 0 > /sys/devices/system/cpu/cpu1/online 
> cpu 1 (hwid 1) Ready to die...
> BUG: using smp_processor_id() in preemptible [00000001] code:
> ksoftirqd/1/5
> caller is .ksoftirqd+0xbc/0x1f8
> Call Trace:
> [c0000000fffbbce0] [ffffffffffffffff] 0xffffffffffffffff (unreliable)
> [c0000000fffbbd60] [c0000000001c9f1c] .smp_processor_id+0x154/0x168
> [c0000000fffbbe20] [c00000000005f414] .ksoftirqd+0xbc/0x1f8
> [c0000000fffbbed0] [c0000000000764cc] .kthread+0x128/0x134
> [c0000000fffbbf90] [c000000000014248] .kernel_thread+0x4c/0x6c
>
> I believe the above warning is caused by the local_softirq_pending
> call on a "foreign" cpu before ksoftirqd/1 has been stopped.  Looking
> at the code, I think this doesn't indicate a real bug, but it would be
> better if ksoftirqd didn't check local_softirq_pending after it's been
> kicked off its cpu, right?
>
>
> # echo 1 > /sys/devices/system/cpu/cpu1/online 
> BUG: using smp_processor_id() in preemptible [00000001] code:
> swapper/0
> caller is .dedicated_idle+0x68/0x22c
> Call Trace:
> [c0000000fffafc50] [ffffffffffffffff] 0xffffffffffffffff (unreliable)
> [c0000000fffafcd0] [c0000000001c9f1c] .smp_processor_id+0x154/0x168
> [c0000000fffafd90] [c00000000000f998] .dedicated_idle+0x68/0x22c
> [c0000000fffafe80] [c00000000000fce8] .cpu_idle+0x34/0x4c
> [c0000000fffaff00] [c00000000003a744] .start_secondary+0x10c/0x150
> [c0000000fffaff90] [c00000000000bd28] .enable_64b_mode+0x0/0x28
>
> Should ppc64 simply use _smp_processor_id() in its idle loop code
> (like i386)?
>
> If I online and offline cpus rapidly enough I can eventually get the
> following:
>
> printk: 49 messages suppressed.
> BUG: using smp_processor_id() in preemptible [00000001] code:
> events/3/1262
> caller is .cache_reap+0x21c/0x2b8
> Call Trace:
> [c0000000ed67bb90] [ffffffffffffffff] 0xffffffffffffffff (unreliable)
> [c0000000ed67bc10] [c0000000001c9f1c] .smp_processor_id+0x154/0x168
> [c0000000ed67bcd0] [c0000000000938e8] .cache_reap+0x21c/0x2b8
> [c0000000ed67bda0] [c00000000006f4bc] .worker_thread+0x230/0x310
> [c0000000ed67bed0] [c0000000000764cc] .kthread+0x128/0x134
> [c0000000ed67bf90] [c000000000014248] .kernel_thread+0x4c/0x6c
>
> And this will repeat over and over even after I stop hotplugging
> cpus...  from the same events thread so I think it's somehow gotten
> "stuck"?
>
> Anything I can do to further debug?
>
>
> Nathan
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
>
>  
Hi!
Use get_cpu() (It disables preemption) or __smp_processor_id () (on a smp).

Matthias-Christian Ott
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/