Re: [PATCH][3.10] nohz: Fix lockup on restart from wrong error code

[Frederic Weisbecker]

2013/5/21 Steven Rostedt <rostedt@xxxxxxxxxxx>:
> commit a382bf934449 "nohz: Assign timekeeping duty to a CPU outside the
> full dynticks range" added a cpu notifier callback that would prevent
> the time keeping CPU from going offline if the have_nohz_full_mask was
> set.
>
> This also prevents the CPU from going offline on system reboot.
>
> Worse yet, the return code was -EINVAL, but the notifier does not
> recognize error codes, and it must be wrapped by a notifier_from_errno()
> function. This means that even though the CPU would fail to go down, the
> notifier would think it succeeded, and the cpu down process would
> continue.
>
> This caused two different problems. One, the migration thread after
> moving tasks from the CPU would park itself and then a task, namely the
> reboot task, could migrate onto that CPU. Then the reboot task spins
> waiting for the cpu to go idle. But because the reboot task happens to
> be spinning on the cpu its waiting for, the system hangs.
>
> The other error that happened was that the sched_domain re-setup would
> get confused, and in get_group() the cpu = cpumask_first() would process
> a mask that had nothing set, and return cpu > nr_cpu_ids. Later it would
> reference the per_cpu sg with this CPU and get a bogus pointer and
> crash.
>
> This fix simply fixes the issue with the return code of the cpu
> notifier. This prevents all non-boot CPUs from going down, but that only
> gives us the following warnings and does not crash or lockup the system.
>
> [   73.655698] _cpu_down: attempt to take down CPU 2 failed
> [   73.661874] Error taking CPU2 down: -22
> [   73.665727] Non-boot CPUs are not disabled
> [   73.669853] Restarting system.
>
> And because of this, we get this warning too. But at least the system
> reboots.
>
> [   73.432740] ------------[ cut here ]------------
> [   73.433003] WARNING: at /home/rostedt/work/git/linux-trace.git/kernel/workqueue.c:4584 workqueue_cpu_up_callback+0x24b/0x48c()
> [   73.433003] Modules linked in: ebtables ipt_MASQUERADE sunrpc bridge stp llc ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ipv6 uinput snd_hda_codec_idt snd_hda_intel snd_hda_codec kvm_intel kvm snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd soundcore snd_page_alloc shpchp i2c_i801 microcode pata_acpi firewire_ohci firewire_core crc_itu_t ata_generic i915 drm_kms_helper drm i2c_algo_bit i2c_core video [last unloaded: ip6_tables]
> [   73.433003] CPU: 0 PID: 2765 Comm: reboot Not tainted 3.10.0-rc2-test+ #124
> [   73.433003] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS SDBLI944.86P 05/08/2007
> [   73.433003]  ffffffff817d0b08 ffff88006a95bc28 ffffffff814ca368 ffff88006a95bc68
> [   73.433003]  ffffffff81035267 0000000000000002 0000000000000000 ffff88007d512e00
> [   73.433003]  0000000000000002 ffff88007a809cc0 ffff88007d513260 ffff88006a95bc78
> [   73.433003] Call Trace:
> [   73.433003]  [<ffffffff814ca368>] dump_stack+0x19/0x1b
> [   73.433003]  [<ffffffff81035267>] warn_slowpath_common+0x67/0x80
> [   73.433003]  [<ffffffff8103529a>] warn_slowpath_null+0x1a/0x1c
> [   73.433003]  [<ffffffff814bee83>] workqueue_cpu_up_callback+0x24b/0x48c
> [   73.433003]  [<ffffffff810679fd>] ? cpumask_weight+0x13/0x14
> [   73.433003]  [<ffffffff814d22dd>] notifier_call_chain+0x37/0x63
> [   73.433003]  [<ffffffff8105c19a>] __raw_notifier_call_chain+0xe/0x10
> [   73.433003]  [<ffffffff810383d8>] __cpu_notify+0x20/0x32
> [   73.433003]  [<ffffffff814b3122>] _cpu_down+0x90/0x229
> [   73.433003]  [<ffffffff81038687>] disable_nonboot_cpus+0x5a/0xfb
> [   73.433003]  [<ffffffff81049d87>] kernel_restart+0x18/0x5a
> [   73.433003]  [<ffffffff81049f52>] SYSC_reboot+0x177/0x1d9
> [   73.433003]  [<ffffffff810ca70a>] ? trace_preempt_on+0x1b/0x2f
> [   73.433003]  [<ffffffff81085eac>] ? trace_hardirqs_on+0xd/0xf
> [   73.433003]  [<ffffffff810e571e>] ? user_exit+0x69/0x70
> [   73.433003]  [<ffffffff810e571e>] ? user_exit+0x69/0x70
> [   73.433003]  [<ffffffff81085e68>] ? trace_hardirqs_on_caller+0x160/0x197
> [   73.433003]  [<ffffffff81085eac>] ? trace_hardirqs_on+0xd/0xf
> [   73.433003]  [<ffffffff8100c7b7>] ? syscall_trace_enter+0xdb/0x1b3
> [   73.433003]  [<ffffffff81049fc2>] SyS_reboot+0xe/0x10
> [   73.433003]  [<ffffffff814d5814>] tracesys+0xdd/0xe2
> [   73.433003] ---[ end trace 1a5fc10dcbddf506 ]---
>
> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

There has been this patch that makes it return -EPERM instead:
https://lkml.org/lkml/2013/5/20/386

Not sure which is best. Both sort of make sense to me.
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