linux-kernel - Re: [PATCH] of.c: replace of_node_put with _

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Message-ID: <CAL_JsqLTDDAtCQ2YeNjUZ6dPJmRtaSEYmYtN2-jAjQFkpKRLfg@mail.gmail.com>
Date: Wed, 7 Aug 2024 10:18:04 -0600
From: Rob Herring <robh@...nel.org>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>, Bjorn Helgaas <helgaas@...nel.org>, 
	David Hunter <david.hunter.linux@...il.com>
Cc: bhelgaas@...gle.com, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org, julia.lawall@...ia.fr, 
	skhan@...uxfoundation.org, javier.carrasco.cruz@...il.com
Subject: Re: [PATCH] of.c: replace of_node_put with __free improves cleanup

On Wed, Aug 7, 2024 at 4:47 AM Jonathan Cameron
<Jonathan.Cameron@...wei.com> wrote:
>
> On Thu, 1 Aug 2024 18:55:26 -0500
> Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> > [+cc Rob, Jonathan]
> >
> > On Fri, Jul 19, 2024 at 06:38:05PM -0400, David Hunter wrote:
> > > The use of the __free function allows the cleanup to be based on scope
> > > instead of on another function called later. This makes the cleanup
> > > automatic and less susceptible to errors later.
> > >
> > > This code was compiled without errors or warnings.
> >
> > I *think* this looks OK, but I'm not comfy with all this scope magic
> > yet, so would like Jonathan and/or Rob to take a peek too.
>
> I'm suspicious of usecases where there isn't a constructor / destructor pair.
>
> This is more of a 'steal' the pointer and destroy it pattern.
>
> Also, bug in this case.... see below.
>
> >
> > And is there some way to include a hint here about how to find the
> > implicit of_node_put()?  I think it's this from 9448e55d032d ("of: Add
> > cleanup.h based auto release via __free(device_node) markings"):
> >
> >   +DEFINE_FREE(device_node, struct device_node *, if (_T) of_node_put(_T))
>
> Yes, it's that one.  Makes sense to add a reference to that in the
> patch description for these.
> >
> > but it did take some looking to find it.
> >
> > If it looks good, I'll tweak the commit log to use imperative mood:
> > https://chris.beams.io/posts/git-commit/
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=v6.9#n94
> >
> > since this technically says what *could* happen but not what the patch
> > *does*.
> >
> > > Signed-off-by: David Hunter <david.hunter.linux@...il.com>
> > > ---
> > >  drivers/pci/of.c | 4 +---
> > >  1 file changed, 1 insertion(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> > > index b908fe1ae951..8b150982f5cd 100644
> > > --- a/drivers/pci/of.c
> > > +++ b/drivers/pci/of.c
> > > @@ -616,16 +616,14 @@ int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge)
> > >
> > >  void of_pci_remove_node(struct pci_dev *pdev)
> > >  {
> > > -   struct device_node *np;
> > > +   struct device_node *np __free(device_node) = pci_device_to_OF_node(pdev);
> > >
> > > -   np = pci_device_to_OF_node(pdev);
> > >     if (!np || !of_node_check_flag(np, OF_DYNAMIC))
>
> Wil now put the node if that second check fails. Didn't do that before
> and I'm guessing we shouldn't?  Technically it calls the cleanup
> in the !np case but that is fine as we check for NULL pointer.
>
> So I'd leave this particular one alone.

Right. The pci_device_to_OF_node() doesn't do a get, so using __free()
isn't really appropriate here. The put here is to free the node. The
get to balance the put was the allocation of the node.

Rob