linux-kernel - Re: [PATCH V3 03/16] platform/x86/intel/vsec: Use cleanup.h

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Message-ID: <4315a8db-16fe-7421-c482-5aede4d5cdd@linux.intel.com>
Date:   Fri, 13 Oct 2023 13:54:14 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     "David E. Box" <david.e.box@...ux.intel.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org, rajvi.jingar@...ux.intel.com
Subject: Re: [PATCH V3 03/16] platform/x86/intel/vsec: Use cleanup.h

On Thu, 12 Oct 2023, David E. Box wrote:

> On Thu, 2023-10-12 at 17:46 +0300, Ilpo Järvinen wrote:
> > On Wed, 11 Oct 2023, David E. Box wrote:
> > 
> > > Use cleanup.h helpers to handle cleanup of resources in
> > > intel_vsec_add_dev() after failures.
> > > 
> > > Signed-off-by: David E. Box <david.e.box@...ux.intel.com>
> > > ---
> > > V3 - New patch.
> > > 
> > >  drivers/platform/x86/intel/vsec.c | 17 ++++++++++-------
> > >  1 file changed, 10 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/drivers/platform/x86/intel/vsec.c
> > > b/drivers/platform/x86/intel/vsec.c
> > > index 15866b7d3117..f03ab89ab7c0 100644
> > > --- a/drivers/platform/x86/intel/vsec.c
> > > +++ b/drivers/platform/x86/intel/vsec.c
> > > @@ -15,6 +15,7 @@
> > >  
> > >  #include <linux/auxiliary_bus.h>
> > >  #include <linux/bits.h>
> > > +#include <linux/cleanup.h>
> > >  #include <linux/delay.h>
> > >  #include <linux/kernel.h>
> > >  #include <linux/idr.h>
> > > @@ -155,10 +156,10 @@ EXPORT_SYMBOL_NS_GPL(intel_vsec_add_aux, INTEL_VSEC);
> > >  static int intel_vsec_add_dev(struct pci_dev *pdev, struct
> > > intel_vsec_header *header,
> > >                               struct intel_vsec_platform_info *info)
> > >  {
> > > -       struct intel_vsec_device *intel_vsec_dev;
> > > +       struct intel_vsec_device __free(kfree) *intel_vsec_dev = NULL;
> > >         struct resource *res, *tmp;
> > >         unsigned long quirks = info->quirks;
> > > -       int i;
> > > +       int ret, i;
> > >  
> > >         if (!intel_vsec_supported(header->id, info->caps))
> > >                 return -EINVAL;
> > > @@ -178,10 +179,8 @@ static int intel_vsec_add_dev(struct pci_dev *pdev,
> > > struct intel_vsec_header *he
> > >                 return -ENOMEM;
> > >  
> > >         res = kcalloc(header->num_entries, sizeof(*res), GFP_KERNEL);
> > > -       if (!res) {
> > > -               kfree(intel_vsec_dev);
> > > +       if (!res)
> > >                 return -ENOMEM;
> > > -       }
> > >  
> > >         if (quirks & VSEC_QUIRK_TABLE_SHIFT)
> > >                 header->offset >>= TABLE_OFFSET_SHIFT;
> > > @@ -208,8 +207,12 @@ static int intel_vsec_add_dev(struct pci_dev *pdev,
> > > struct intel_vsec_header *he
> > >         else
> > >                 intel_vsec_dev->ida = &intel_vsec_ida;
> > >  
> > > -       return intel_vsec_add_aux(pdev, NULL, intel_vsec_dev,
> > > -                                 intel_vsec_name(header->id));
> > > +       ret = intel_vsec_add_aux(pdev, NULL, intel_vsec_dev,
> > > +                                intel_vsec_name(header->id));
> > > +
> > > +       no_free_ptr(intel_vsec_dev);
> > > +
> > > +       return ret;
> > 
> > So if intel_vsec_add_aux() returned an error, intel_vsec_dev won't be 
> > freed because of the call call to no_free_ptr() before return. I that's 
> > not what you intended?
> 
> It will have been freed if intel_vsec_add_aux() fails. It's a little messy. That
> function creates the auxdev and assigns the release function which will free
> intel_vsec_dev when the device is removed. But there are failure points that
> will also invoke the release function. Because of this, for all the failure
> points in that function we free intel_vsec_dev so that it's state doesn't need
> to be questioned here. This happens explicitly if the failure is before
> auxiliary_device_init(), or through the release function invoked by
> auxiliary_device_uninit() if after.

Oh, that's really convoluted and no wonder I missed it completely. It 
might even be that using cleanup.h here isn't really worth it. I know 
I pushed you into that direction but I didn't realize all the complexity
at that point.

If you still want to keep using cleanup.h, it would perhaps be less 
dangerous if you change the code such that no_free_ptr() for
intel_vsec_dev and the resource (in 4/16, that's a similar case, isn't 
it?) are before the intel_vsec_add_aux() call (and I'd also add a comment 
to explain that freeing them is now responsability of 
intel_vsec_add_aux()). That way, we don't leave a trap into there where 
somebody happily adds another no_free_ptr() to the same group and it 
causes a mem leak.


-- 
 i.