Re: [PATCH] PCI: endpoint: pci-epf-test: Make use of cached 'epc_features' in pci_epf_test_core_init()

Manivannan Sadhasivam
2024-04-18T05:47:15Z

On Wed, Apr 17, 2024 at 07:54:56PM +0200, Niklas Cassel 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@linaro.org>
> > > Closes: https://lore.kernel.org/linux-pci/024b5826-7180-4076-ae08-57d2584cca3f@moroto.mountain/
> > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> >
> > I think you forgot:
> > Fixes: a01e7214bef9 ("PCI: endpoint: Remove "core_init_notifier" flag")
> >
> >
> > > ---
> > > 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().)
>
> ...or just kill the local variables:
> bool msi_capable/msix_capable in pci_epf_test_core_init(), and
> bool msix_capable pci_epf_test_alloc_space()
> and just do:
>
> if (epc_features->msix_capable) / if (epc_features->msi_capable)
>
> directly?
>

Yeah, that will also work.

- Mani

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