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

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 [off-list ref]:

Hi Antonio,

On Fri, 2012-01-13 at 14:17 -0500, Antonio Barbalace wrote:

quoted

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