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Date:   Tue, 31 Mar 2020 17:28:50 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Russell King <rmk+kernel@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH 6/9] lockdep: Introduce wait-type checks
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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.