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Date:   Wed, 17 Feb 2021 21:50:38 +0000
Message-ID: <87czwys6s1.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Michael Walle <michael@walle.cc>
Cc:     gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
        tglx@linutronix.de
Subject: Re: [PATCH] irqdomain: remove debugfs_file from struct irq_domain
In-Reply-To: <5c527bfb6f3dfe31b5c25f29418306c6@walle.cc>
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        <20210217195717.13727-1-michael@walle.cc>
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        <5c527bfb6f3dfe31b5c25f29418306c6@walle.cc>
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On Wed, 17 Feb 2021 20:10:50 +0000,
Michael Walle <michael@walle.cc> wrote:
> 
> Am 2021-02-17 21:02, schrieb Marc Zyngier:
> > On 2021-02-17 19:57, Michael Walle wrote:
> >> Hi Greg,
> >> 
> >>> There's no need to keep around a dentry pointer to a simple file that
> >>> debugfs itself can look up when we need to remove it from the system.
> >>> So simplify the code by deleting the variable and cleaning up the
> >>> logic
> >>> around the debugfs file.
> >> 
> >> This will generate the following oops on my board (arm64,
> >> freescale/fsl-ls1028a-kontron-sl28-var3-ads2.dts). In debugfs_lookup()
> >> debugfs_mount is NULL.
> > 
> > That's odd. I gave it a go yesterday, and nothing blew up.
> > Which makes me wonder whether I had the debug stuff enabled
> > the first place...
> > 
> > I've dropped the patch from -next for now until I figure it out
> > (probably tomorrow).
> 
> Mh, maybe its my .config, I've attached it. I also noticed that
> the board boots just fine in our kernel-ci [1].

I reproduced here. I had disabled GENERIC_IRQ_DEBUGFS for obscure
reasons, and it caught fire as I re-enabled it.

Adding this fixes it for me:

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 367ff1c35f75..d8a14cf1a7b6 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -1904,7 +1904,8 @@ static void debugfs_add_domain_dir(struct irq_domain *d)
 
 static void debugfs_remove_domain_dir(struct irq_domain *d)
 {
-	debugfs_remove(debugfs_lookup(d->name, domain_dir));
+	if (domain_dir)
+		debugfs_remove(debugfs_lookup(d->name, domain_dir));
 }
 
 void __init irq_domain_debugfs_init(struct dentry *root)


Could you please check whether it works for you?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.