Re: 9908859acaa9 cpuidle/menu: add per CPU PM QoS resume latency consideration

[Mike Galbraith]

On Wed, 2017-02-22 at 14:12 +0100, Peter Zijlstra wrote:
> On Wed, Feb 22, 2017 at 01:56:37PM +0100, Mike Galbraith wrote:
> > Hi,
> > 
> > Do we really need a spinlock for that in the idle loop?
> 
> Urgh, that's broken on RT, you cannot schedule the idle loop.

That's what made me notice the obnoxious little bugger.

[   77.608340] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:995
[   77.608342] in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/1
[   77.608343] INFO: lockdep is turned off.
[   77.608344] irq event stamp: 59222
[   77.608353] hardirqs last  enabled at (59221): [<ffffffff81105a1f>] rcu_idle_exit+0x2f/0x50
[   77.608362] hardirqs last disabled at (59222): [<ffffffff810d4f1a>] do_idle+0x9a/0x290
[   77.608372] softirqs last  enabled at (0): [<ffffffff8107b8f1>] copy_process.part.34+0x5f1/0x22a0
[   77.608374] softirqs last disabled at (0): [<          (null)>]           (null)
[   77.608374] Preemption disabled at:
[   77.608383] [<ffffffff817282b2>] schedule_preempt_disabled+0x22/0x30
[   77.608387] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G        W   E   4.11.0-rt9-rt #163
[   77.608389] Hardware name: Intel Corporation BRICKLAND/BRICKLAND, BIOS BRHSXSD1.86B.0056.R01.1409242327 09/24/2014
[   77.608390] Call Trace:
[   77.608399]  dump_stack+0x85/0xc8
[   77.608405]  ___might_sleep+0x15d/0x260
[   77.608409]  rt_spin_lock+0x24/0x80
[   77.608419]  dev_pm_qos_read_value+0x1e/0x40
[   77.608424]  menu_select+0x56/0x3e0
[   77.608426]  ? rcu_eqs_enter_common.isra.40+0x9d/0x160
[   77.608435]  cpuidle_select+0x13/0x20
[   77.608438]  do_idle+0x182/0x290
[   77.608445]  cpu_startup_entry+0x48/0x50
[   77.608450]  start_secondary+0x133/0x160
[   77.608453]  start_cpu+0x14/0x14