Re: possible circular locking dependency backtrace seen when enabling PREEMPT_RT

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2025-02-12 12:18:37 [-0500], Steven Rostedt wrote:
> On Wed, 12 Feb 2025 18:09:55 +0100
> Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> 
> > > Why not? It keeps the same paradigm as non PREEMPT_RT. Do we really want to
> > > litter local_bh_disable around all these cases that spin_lock_irq*() is
> > > used to disable bh?  
> > 
> > Yes.
> 
> OK, after testing that patch I see the issue. The local_bh_disable() makes
> it look like we are in a softirq, and that triggers a bunch of
> BUG(in_interrupt()) that are around the kernel.
> 
> Couldn't we make the spin_lock_irq*() also disable softirqs without making
> softirq_count() return true?

Maybe. But I don't see the advantage. See my other reply.

> That would keep the same paradigm between non-PREEMPT_RT as well as
> PREEMPT_RT without having to litter these all over the place.

I am working on getting rid of the lock in local_bh_disable(). Guess
what happens then in terms of "same paradigm".

> -- Steve

Sebastian