Re: [PATCH 6/9] lockdep: Introduce wait-type checks

[Peter Zijlstra]

On Tue, Mar 31, 2020 at 04:55:15PM +0200, Peter Zijlstra wrote:
> On Tue, Mar 31, 2020 at 03:25:21PM +0200, Geert Uytterhoeven wrote:
> > On arm64 (e.g. R-Car H3 ES2.0):
> > 
> > +=============================
> > +[ BUG: Invalid wait context ]
> > +5.6.0-salvator-x-09423-gb29514ba13a9c459-dirty #679 Not tainted
> > +-----------------------------
> > +swapper/5/0 is trying to lock:
> > +ffffff86ff76f398 (&pool->lock){..-.}-{3:3}, at: __queue_work+0x134/0x430
> > +other info that might help us debug this:
> > +1 lock held by swapper/5/0:
> > + #0: ffffffc01103a4a0 (rcu_read_lock){....}-{1:3}, at:
> > rcu_lock_acquire.constprop.59+0x0/0x38
> > +stack backtrace:
> > +CPU: 5 PID: 0 Comm: swapper/5 Not tainted
> > 5.6.0-salvator-x-09423-gb29514ba13a9c459-dirty #679
> > +Hardware name: Renesas Salvator-X 2nd version board based on r8a77951 (DT)
> > +Call trace:
> > + dump_backtrace+0x0/0x180
> > + show_stack+0x14/0x1c
> > + dump_stack+0xdc/0x12c
> > + __lock_acquire+0x37c/0xf9c
> > + lock_acquire+0x258/0x288
> > + _raw_spin_lock+0x34/0x48
> > + __queue_work+0x134/0x430
> > + queue_work_on+0x48/0x8c
> > + timers_update_nohz+0x24/0x2c
> > + tick_nohz_activate.isra.15.part.16+0x5c/0x80
> > + tick_setup_sched_timer+0xe0/0xf0
> > + hrtimer_run_queues+0x88/0xf8
> 
> So this is complaining that it cannot take pool->lock, which is
> WAIT_CONFIG while holding RCU, which presents a WAIT_CONFIG context.
> 
> This seems to implicate something is amiss, because that should be
> allowed. The thing it doesn't print is the context, which in the above
> case is a (hrtimer) interrupt.
> 
> I suspect this really is a hardirq context and the next patch won't cure
> things. It looks nohz (full?) related.
> 
> Frederic, can you untangle this?

Sebastian is right; I completely forgot the workqueue thing was still
pending.