linux-kernel - Re: [PATCH] PCI: endpoint: pci-epf-test: Make use of cached 'epc_features' in pci_epf_test_core

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Message-ID: <ZiDB18w4bnUCSH7D@ryzen>
Date: Thu, 18 Apr 2024 08:46:47 +0200
From: Niklas Cassel <cassel@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Krzysztof Wilczyński <kw@...ux.com>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] PCI: endpoint: pci-epf-test: Make use of cached
 'epc_features' in pci_epf_test_core_init()

On Thu, Apr 18, 2024 at 11:13:19AM +0530, Manivannan Sadhasivam wrote:
> On Wed, Apr 17, 2024 at 07:49:45PM +0200, Niklas Cassel wrote:
> > On Wed, Apr 17, 2024 at 10:47:25PM +0530, Manivannan Sadhasivam wrote:
> > > Instead of getting the epc_features from pci_epc_get_features() API, use
> > > the cached pci_epf_test::epc_features value to avoid the NULL check. Since
> > > the NULL check is already performed in pci_epf_test_bind(), having one more
> > > check in pci_epf_test_core_init() is redundant and it is not possible to
> > > hit the NULL pointer dereference. This also leads to the following smatch
> > > warning:
> > > 
> > > drivers/pci/endpoint/functions/pci-epf-test.c:784 pci_epf_test_core_init()
> > > error: we previously assumed 'epc_features' could be null (see line 747)
> > > 
> > > Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> > > Closes: https://lore.kernel.org/linux-pci/024b5826-7180-4076-ae08-57d2584cca3f@moroto.mountain/
> > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > 
> > I think you forgot:
> > Fixes: a01e7214bef9 ("PCI: endpoint: Remove "core_init_notifier" flag")
> > 
> 
> No, that's not the correct fixes tag I suppose. This redudant check is
> introduced by commit, 5e50ee27d4a5 ("PCI: pci-epf-test: Add support to defer
> core initialization") and this commit removes the redundant check (fixing smatch
> warning is a side effect). So if the fixes tag needs to be added, then this
> commit should be referenced.

Well, you have a Closes: tag that links to a bug report about a smatch
warning that was introduced with 5e50ee27d4a5 ("PCI: pci-epf-test: Add
support to defer core initialization").

So if you want to reference another commit, then you should probably
drop the Closes: tag.


> 
> > 
> > > ---
> > >  drivers/pci/endpoint/functions/pci-epf-test.c | 9 ++++-----
> > >  1 file changed, 4 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> > > index 977fb79c1567..0d28f413cb07 100644
> > > --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> > > +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> > > @@ -743,11 +743,10 @@ static int pci_epf_test_core_init(struct pci_epf *epf)
> > >  	bool msi_capable = true;
> > >  	int ret;
> > >  
> > > -	epc_features = pci_epc_get_features(epc, epf->func_no, epf->vfunc_no);
> > > -	if (epc_features) {
> > > -		msix_capable = epc_features->msix_capable;
> > > -		msi_capable = epc_features->msi_capable;
> > > -	}
> > > +	epc_features = epf_test->epc_features;
> > 
> > How about:
> > 
> > index 977fb79c1567..4d6105c07ac0 100644
> > --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> > +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> > @@ -735,7 +735,7 @@ static int pci_epf_test_core_init(struct pci_epf *epf)
> >  {
> >         struct pci_epf_test *epf_test = epf_get_drvdata(epf);
> >         struct pci_epf_header *header = epf->header;
> > -       const struct pci_epc_features *epc_features;
> > +       const struct pci_epc_features *epc_features = epf_test->epc_features;
> >         struct pci_epc *epc = epf->epc;
> >         struct device *dev = &epf->dev;
> >         bool linkup_notifier = false;
> > @@ -743,12 +743,6 @@ static int pci_epf_test_core_init(struct pci_epf *epf)
> >         bool msi_capable = true;
> >         int ret;
> >  
> > -       epc_features = pci_epc_get_features(epc, epf->func_no, epf->vfunc_no);
> > -       if (epc_features) {
> > -               msix_capable = epc_features->msix_capable;
> > -               msi_capable = epc_features->msi_capable;
> > -       }
> > -
> >         if (epf->vfunc_no <= 1) {
> >                 ret = pci_epc_write_header(epc, epf->func_no, epf->vfunc_no, header);
> >                 if (ret) {
> > @@ -761,6 +755,7 @@ static int pci_epf_test_core_init(struct pci_epf *epf)
> >         if (ret)
> >                 return ret;
> >  
> > +       msi_capable = epc_features->msi_capable;
> >         if (msi_capable) {
> >                 ret = pci_epc_set_msi(epc, epf->func_no, epf->vfunc_no,
> >                                       epf->msi_interrupts);
> > @@ -770,6 +765,7 @@ static int pci_epf_test_core_init(struct pci_epf *epf)
> >                 }
> >         }
> >  
> > +       msix_capable = epc_features->msix_capable;
> >         if (msix_capable) {
> >                 ret = pci_epc_set_msix(epc, epf->func_no, epf->vfunc_no,
> >                                        epf->msix_interrupts,
> > @@ -814,11 +810,9 @@ static int pci_epf_test_alloc_space(struct pci_epf *epf)
> >         void *base;
> >         enum pci_barno test_reg_bar = epf_test->test_reg_bar;
> >         enum pci_barno bar;
> > -       const struct pci_epc_features *epc_features;
> > +       const struct pci_epc_features *epc_features = epf_test->epc_features;
> >         size_t test_reg_size;
> >  
> > -       epc_features = epf_test->epc_features;
> > -
> >         test_reg_bar_size = ALIGN(sizeof(struct pci_epf_test_reg), 128);
> >  
> >         msix_capable = epc_features->msix_capable;
> > 
> > 
> > Instead?
> > 
> > That way, we assign msi_capable/msix_capable just before the if-statement
> > where it is used. (Which matches how we already assign msix_capable just
> > before the if-statement in pci_epf_test_alloc_space().)
> > 
> 
> Ok, if we go with this pattern, then pci_epf_test_set_bar() also needs to be
> updated.

pci_epf_test_set_bar() ? I presume that you mean pci_epf_test_alloc_space().

How about a 1/2 patch that modifies pci_epf_test_core_init() and Closes: the
bug report, and a 2/2 patch that modifies pci_epf_test_alloc_space() ?


Kind regards,
Niklas