linux-kernel - Re: [BUG] -next lockdep invalid wait context

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Message-ID: <186804c5-0ebd-4d38-b9ad-bfb74e39b353@paulmck-laptop>
Date: Thu, 31 Oct 2024 10:50:29 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Vlastimil Babka <vbabka@...e.cz>, Marco Elver <elver@...gle.com>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	kasan-dev@...glegroups.com, linux-mm@...ck.org,
	sfr@...b.auug.org.au, longman@...hat.com, boqun.feng@...il.com,
	cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
	iamjoonsoo.kim@....com, akpm@...ux-foundation.org
Subject: Re: [BUG] -next lockdep invalid wait context

On Thu, Oct 31, 2024 at 08:55:09AM +0100, Sebastian Andrzej Siewior wrote:
> On 2024-10-31 08:35:45 [+0100], Vlastimil Babka wrote:
> > On 10/31/24 08:21, Sebastian Andrzej Siewior wrote:
> > > On 2024-10-30 16:10:58 [-0700], Paul E. McKenney wrote:
> > >> 
> > >> So I need to avoid calling kfree() within an smp_call_function() handler?
> > > 
> > > Yes. No kmalloc()/ kfree() in IRQ context.
> > 
> > However, isn't this the case that the rule is actually about hardirq context
> > on RT, and most of these operations that are in IRQ context on !RT become
> > the threaded interrupt context on RT, so they are actually fine? Or is smp
> > call callback a hardirq context on RT and thus it really can't do those
> > operations?
> 
> interrupt handlers as of request_irq() are forced-threaded on RT so you
> can do kmalloc()/ kfree() there. smp_call_function.*() on the other hand
> are not threaded and invoked directly within the IRQ context.

OK, thank you all for the explanation!  I will fix using Boqun's
suggestion of irq work, but avoiding the issue Boqun raises by invoking
the irq-work handler from the smp_call_function() handler.

It will be a few days before I get to this, so if there is a better way,
please do not keep it a secret!

							Thanx, Paul