Re: [-next] Lockdep warnings

[Mark Rutland]

On Tue, Jul 26, 2022 at 11:41:34AM +0100, Sudeep Holla wrote:
> I was seeing the below lockdep warnings on my arm64 Juno development
> platform almost 2 weeks back with -next. I wanted to check for similar
> reports before post and forgot.

[...]

> However I don't see the above warning with the latest -next. When I tried
> yesterday's -next now, I see a different warning. Not sure if they are
> related. I haven't tried to bisect.
> 
> --->8
> =============================
> [ BUG: Invalid wait context ]
> 5.19.0-rc8-next-20220725 #38 Not tainted
> -----------------------------
> swapper/0/0 is trying to lock:
> (&drvdata->spinlock){....}-{3:3}, at: cti_cpu_pm_notify+0x54/0x114

Hmmm... do you have CONFIG_PROVE_RAW_LOCK_NESTING enabled?

IIUC that should be {2:2} otherwise...

> other info that might help us debug this:
> context-{5:5}
> 1 lock held by swapper/0/0:
>  #0: (cpu_pm_notifier.lock){....}-{2:2}, at: cpu_pm_enter+0x2c/0x80

... and this is telling us that we're trying to take a regular spinlock under a
raw spinlock, which is not as intended.

The Kconfig text notes:

         NOTE: There are known nesting problems. So if you enable this 
         option expect lockdep splats until these problems have been fully
         addressed which is work in progress. This config switch allows to
         identify and analyze these problems. It will be removed and the
         check permanently enabled once the main issues have been fixed.

... and I suspect this is one of those latent issues.

Mark.

> stack backtrace:
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.19.0-rc8-next-20220725-00004-g599e6691ed8c #38
> Call trace:
>  dump_backtrace+0xe8/0x108
>  show_stack+0x18/0x4c
>  dump_stack_lvl+0x90/0xc8
>  dump_stack+0x18/0x54
>  __lock_acquire+0xa70/0x32d0
>  lock_acquire+0x160/0x308
>  _raw_spin_lock+0x60/0xa0
>  cti_cpu_pm_notify+0x54/0x114
>  raw_notifier_call_chain_robust+0x50/0xd4
>  cpu_pm_enter+0x48/0x80
>  psci_enter_idle_state+0x34/0x74
>  cpuidle_enter_state+0x120/0x2a8
>  cpuidle_enter+0x38/0x50
>  do_idle+0x1e8/0x2b8
>  cpu_startup_entry+0x24/0x28
>  kernel_init+0x0/0x1a0
>  start_kernel+0x0/0x470
>  start_kernel+0x34c/0x470
>  __primary_switched+0xbc/0xc4
> 
> ----
> 
> --
> Regards,
> Sudeep