linux-kernel - Re: [PATCH] irqdomain: remove debugfs_file from struct irq

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Date:   Thu, 18 Feb 2021 09:38:30 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Michael Walle <michael@...le.cc>
Cc:     Marc Zyngier <maz@...nel.org>, linux-kernel@...r.kernel.org,
        tglx@...utronix.de
Subject: Re: [PATCH] irqdomain: remove debugfs_file from struct irq_domain

On Thu, Feb 18, 2021 at 09:27:09AM +0100, Michael Walle wrote:
> Am 2021-02-18 08:31, schrieb Greg KH:
> > On Wed, Feb 17, 2021 at 09:50:38PM +0000, Marc Zyngier wrote:
> > > On Wed, 17 Feb 2021 20:10:50 +0000,
> > > Michael Walle <michael@...le.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?
> > 
> > Can you try this debugfs core change instead?  Callers to debugfs should
> > not have to do the above type of checking as debugfs should be much more
> > robust than that.
> > 
> > thanks,
> > 
> > greg k-h
> > 
> > 
> > diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> > index 2fcf66473436..5aa798f52b6e 100644
> > --- a/fs/debugfs/inode.c
> > +++ b/fs/debugfs/inode.c
> > @@ -297,7 +297,7 @@ struct dentry *debugfs_lookup(const char *name,
> > struct dentry *parent)
> >  {
> >  	struct dentry *dentry;
> > 
> > -	if (IS_ERR(parent))
> > +	if (IS_ERR_OR_NULL(name) || IS_ERR(parent))
> >  		return NULL;
> > 
> >  	if (!parent)
> 
> This doesn't work. name is not NULL when it is called.

Ok, but it is a good check we need to make anyway, I'll add it to a
patch series :)

> What has to happen before debugfs_lookup() can be called? Looks like
> someone has to initialize the static debugfs_mount, first.

Wow, wait, you are removing a debugfs file _before_ debugfs is even
initialized?  Didn't expect that, ok, let me go try this again...

thanks,

greg k-h