linux-kernel - Re: [GIT pull] CPU hotplug updates for 4.9

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Date:   Thu, 9 Mar 2017 18:43:58 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Bart Van Assche <Bart.VanAssche@...disk.com>
cc:     "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [GIT pull] CPU hotplug updates for 4.9

On Thu, 9 Mar 2017, Bart Van Assche wrote:
> On Thu, 2017-03-09 at 11:22 +0100, Thomas Gleixner wrote:
> > > In contrast with previous tests this morning I have been able to reproduce
> > > this hang with kernel v4.10. So it's not a kernel v4.10 regression. But the
> > > hang did not occur in a test with kernel v4.9.7. I assume this means that
> > > the regression got introduced between the v4.9 and v4.10 kernels.
> > 
> > Is it always the x86_pkg_thermal init which locks up?
> 
> Hello Thomas,
> 
> Apparently not. Here are a few other call traces that appeared in the system
> log:
> 
> INFO: task systemd-udevd:748 blocked for more than 480 seconds.
>       Tainted: G          IO    4.11.0-rc1-dbg+ #1
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> systemd-udevd   D    0   748    518 0x00000104
> Call Trace:
>  __schedule+0x302/0xc30
>  schedule+0x38/0x90
>  schedule_timeout+0x255/0x490
>  wait_for_completion+0x103/0x170
>  cpuhp_issue_call+0xb9/0xe0
>  __cpuhp_setup_state+0xf6/0x180
>  coretemp_init+0x8d/0x1000 [coretemp]
>  do_one_initcall+0x3e/0x170
>  do_init_module+0x5a/0x1ed
>  load_module+0x2339/0x2a40
>  SYSC_finit_module+0xbc/0xf0
>  SyS_finit_module+0x9/0x10
>  do_syscall_64+0x57/0x140
>  entry_SYSCALL64_slow_path+0x25/0x25
> Showing all locks held in the system:
> 2 locks held by khungtaskd/91:
>  #0:  (rcu_read_lock){......}, at: [<ffffffff8111a6f0>] watchdog+0xa0/0x5d0
>  #1:  (tasklist_lock){.+.?..}, at: [<ffffffff810bf36d>] debug_show_all_locks+0x3d/0x1a0
> 1 lock held by systemd-udevd/748:
>  #0:  (cpu_hotplug.dep_map){++++++}, at: [<ffffffff8106712d>] get_online_cpus+0x2d/0x80

Ok, so it's random. Now it would be interesting what the rest of the system
does when this happens. I still have no idea why that IOAT setting has any
influence.

Thanks,

	tglx