linux-kernel - Re: [PATCH v2 1/2] PCI: endpoint: pci-epf-test: Make use of cached 'epc_features' in pci_epf_test_core

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Message-ID: <ZiEkr3uTLK9B1jGx@lizhi-Precision-Tower-5810>
Date: Thu, 18 Apr 2024 09:48:31 -0400
From: Frank Li <Frank.li@....com>
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>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Niklas Cassel <cassel@...nel.org>,
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH v2 1/2] PCI: endpoint: pci-epf-test: Make use of cached
 'epc_features' in pci_epf_test_core_init()

On Thu, Apr 18, 2024 at 01:29:58PM +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.
> 
> Also with commit a01e7214bef9 ("PCI: endpoint: Remove "core_init_notifier"
> flag"), 'epc_features' got dereferenced without the NULL check, leading to
> the following false positive 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)
> 
> So let's remove the redundant NULL check and also use the epc_features::
> {msix_capable/msi_capable} flags directly to avoid local variables.
> 
> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> Closes: https://lore.kernel.org/linux-pci/024b5826-7180-4076-ae08-57d2584cca3f@moroto.mountain/
> Fixes: 5e50ee27d4a5 ("PCI: pci-epf-test: Add support to defer core initialization")
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Reviewed-by: Frank Li <Frank.Li@....com>

> ---
>  drivers/pci/endpoint/functions/pci-epf-test.c | 14 +++-----------
>  1 file changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> index 977fb79c1567..546d2a27955c 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> @@ -735,20 +735,12 @@ 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;
> -	bool msix_capable = false;
> -	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) {
> @@ -761,7 +753,7 @@ static int pci_epf_test_core_init(struct pci_epf *epf)
>  	if (ret)
>  		return ret;
>  
> -	if (msi_capable) {
> +	if (epc_features->msi_capable) {
>  		ret = pci_epc_set_msi(epc, epf->func_no, epf->vfunc_no,
>  				      epf->msi_interrupts);
>  		if (ret) {
> @@ -770,7 +762,7 @@ static int pci_epf_test_core_init(struct pci_epf *epf)
>  		}
>  	}
>  
> -	if (msix_capable) {
> +	if (epc_features->msix_capable) {
>  		ret = pci_epc_set_msix(epc, epf->func_no, epf->vfunc_no,
>  				       epf->msix_interrupts,
>  				       epf_test->test_reg_bar,
> 
> -- 
> 2.25.1
>