Re: 3.0.10-rt27 arch/arm/kernel/smp.c bug

Antonio Barbalace
2012-01-18T14:29:14Z

Hi Steve,

the problem always happen putting the cpu to sleep on ARM OMAP
platform (I am currently using a Pandaboard), i.e. after
echo 0 > /sys/devices/system/cpu/cpu1/online

Thanks a lot for your help,
Antonio

---

Quoting Steven Rostedt <rostedt@goodmis.org>:

> Hi Antonio,
>
> On Fri, 2012-01-13 at 14:17 -0500, Antonio Barbalace wrote:
>> I would like to report the following bug that is not still solved in
>> the current 3.0.14 ver.
>>
>> [ 300.459960] BUG: sleeping function called from invalid context at
>> kernel/rtm5
>> [ 300.459991] in_atomic(): 1, irqs_disabled(): 128, pid: 9, name:
>> migration/1
>> [ 300.459991] 1 lock held by migration/1/9:
>> [ 300.459991] #0: (tasklist_lock){++++..}, at: [<c0064fe8>]
>> __cpu_disable+0x0
>> [ 300.460021] irq event stamp: 1887
>> [ 300.460052] hardirqs last enabled at (1886): [<c04e5878>]
>> _raw_spin_unlock_8
>> [ 300.460052] hardirqs last disabled at (1887): [<c00efd10>]
>> stop_machine_cpu_4
>> [ 300.460083] softirqs last enabled at (0): [<c009f628>]
>> copy_process+0x3b4/00
>> [ 300.460113] softirqs last disabled at (0): [< (null)>] (null)
>> [ 300.460144] [<c00670e4>] (unwind_backtrace+0x0/0xf4) from
>> [<c04e4c88>] (__rt)
>> [ 300.460174] [<c04e4c88>] (__rt_spin_lock+0x18/0x2c) from
>> [<c04e51e0>] (rt_re)
>> [ 300.460174] [<c04e51e0>] (rt_read_lock+0x54/0x68) from [<c0064fe8>]
>> (__cpu_d)
>> [ 300.460235] [<c0064fe8>] (__cpu_disable+0xdc/0x170) from
>> [<c04d4b7c>] (take_)
>> [ 300.460235] [<c04d4b7c>] (take_cpu_down+0xc/0x30) from [<c00efd28>]
>> (stop_ma)
>> [ 300.460235] [<c00efd28>] (stop_machine_cpu_stop+0xd8/0x114) from
>> [<c00efad4>)
>> [ 300.460266] [<c00efad4>] (cpu_stopper_thread+0xb8/0x1ac) from
>> [<c00c29f8>] ()
>> [ 300.460327] [<c00c29f8>] (kthread+0x88/0x90) from [<c0060914>]
>> (kernel_threa)
>> [ 300.464385] CPU1: shutdown
>>
>> This is due to the following arch/arm/kernel/smp.c @ __cpu_disable code:
>>
>> 169 read_lock(&tasklist_lock);
>> 170 for_each_process(p) {
>> 171 if (p->mm)
>> 172 cpumask_clear_cpu(cpu, mm_cpumask(p->mm));
>> 173 }
>> 174 read_unlock(&tasklist_lock);
>>
>> I am not a rt expert, do you have any clue on how to solve this problem?
>
> Hmm, I'll need to look at this code deeper. The read_lock() in -rt can
> sleep, and this is being called to shutdown a CPU, which I'm sure
> disables interrupts along the way.
>
> What did you do to cause this? Does this happen when you take CPU 1
> offline?
>
> -- Steve
>
>
>