Re: [PATCH] arm/mach-omap2/display: fix possible object referenceleak

[<wen.yang99@zte.com.cn>]

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Hi,
> > Adding devicetree list, Julia, Rob and Tomi to Cc.
> >
> > * Peng Hao <peng.hao2@zte.com.cn> [190212 23:11]:
> > > of_find_device_by_node() takes a reference to the struct device
> > > when it finds a match via get_device.When returning error we should
> > > call put_device.
> > >
> > > Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
> > > ---
> > >  arch/arm/mach-omap2/display.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/arch/arm/mach-omap2/display.c b/arch/arm/mach-omap2/display.c
> > > index f86b72d..c6aa9ed 100644
> > > --- a/arch/arm/mach-omap2/display.c
> > > +++ b/arch/arm/mach-omap2/display.c
> > > @@ -258,6 +258,7 @@ static int __init omapdss_init_of(void)
> > >      r = of_platform_populate(node, NULL, NULL, &pdev->dev);
> > >      if (r) {
> > >          pr_err("Unable to populate DSS submodule devices\n");
> > > +        put_device(&pdev->dev);
> > >          return r;
> > >      }
> >
> > In general, if the device tree node is never used afterwards,
> > should this be just:
> >
> >     r = of_platform_populate(node, NULL, NULL, &pdev->dev);
> >     of_node_put(dev_node);
> 
> Are these solving the same problems?  The of_node_put looks clearly
> necessary, whether there is a success or failure.  I'm not familiar with
> put_device.  I see that it does a kobject_put, but I don't know what
> happens because of that.  But it looks like an inconsistency that Peng's
> patch only considers the failure case, while your suggestion happens
> always.
>
> I guess Peng's patch is motivated by a Coccinelle script that Wen Yang
> (also from ZTE) has been working on.  Perhaps there is a need to adjust
> what is suggested by that script.

Yes, Peng Hao and I belong to the same company.
I found some code issues with this Coccinelle script:
Https://lkml.org/lkml/2019/2/16/107
Our other colleagues are submitting some patches to fix these discovered problems.

For this code(arch/arm/mach-omap2/display.c), there may be two issues:
1, the of_find_device_by_node() takes a reference to the underlying device
structure, we should call put_device()  release that reference.
2, of_find_compatible_node/of_find_node_by_name/of_parse_phandle...  will 
increase the refcount of device_node,  we should call of_node_put() to release
the refcount.

The first issue can already be detected by the Coccinelle script described above;
The second issue, we are still looking for ways to develop the corresponding Coccinelle script.

Regards,
  Wen