Re: sched_core_balance() releasing interrupts with pi_lock held

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 8 Mar 2022 16:14:55 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> Hi Peter,

Have you had time to look into this?

Thanks,

-- Steve

> 
> A ChromeOS bug report showed a lockdep splat that I first thought was a bad
> backport. But when looking at upstream, I don't see how it would work there
> either. The lockdep splat had:
> 
> [56064.673346] Call Trace:
> [56064.676066]  dump_stack+0xb9/0x117
> [56064.679861]  ? print_usage_bug+0x2af/0x2c2
> [56064.684434]  mark_lock_irq+0x25e/0x27d
> [56064.688618]  mark_lock+0x11a/0x16c
> [56064.692412]  mark_held_locks+0x57/0x87
> [56064.696595]  ? _raw_spin_unlock_irq+0x2c/0x40
> [56064.701460]  lockdep_hardirqs_on+0xb1/0x19d
> [56064.706130]  _raw_spin_unlock_irq+0x2c/0x40
> [56064.710799]  sched_core_balance+0x8a/0x4af
> [56064.715369]  ? __balance_callback+0x1f/0x9a
> [56064.720030]  __balance_callback+0x4f/0x9a
> [56064.724506]  rt_mutex_setprio+0x43a/0x48b
> [56064.728982]  task_blocks_on_rt_mutex+0x14d/0x1d5
> 
> Where I see:
> 
> task_blocks_on_rt_mutex() {
>   spin_lock(pi_lock);
>   rt_mutex_setprio() {
>     balance_callback() {
>       sched_core_balance() {
>         spin_unlock_irq(rq);
> 
> Where spin_unlock_irq() enables interrupts while holding the pi_lock, and
> BOOM, lockdep (rightfully) complains.
> 
> The above was me looking at mainline, not the kernel that blew up. So, I'm
> guessing that this is a bug in mainline as well.
> 
> -- Steve