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

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Message-ID: <20241031075509.hCS9Amov@linutronix.de>
Date: Thu, 31 Oct 2024 08:55:09 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: "Paul E. McKenney" <paulmck@...nel.org>, 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 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.

> Vlastimil
> 
Sebastian