linux-kernel - RE: [PATCH 11/14 v3] PCI/PM: Check return value of pcie_capability_read

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Date:   Tue, 14 Jul 2020 08:10:00 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Saheed Olayemi Bolarinwa' <refactormyself@...il.com>,
        "helgaas@...nel.org" <helgaas@...nel.org>
CC:     "bjorn@...gaas.com" <bjorn@...gaas.com>,
        "skhan@...uxfoundation.org" <skhan@...uxfoundation.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel-mentees@...ts.linuxfoundation.org" 
        <linux-kernel-mentees@...ts.linuxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 11/14 v3] PCI/PM: Check return value of
 pcie_capability_read_*()

> From: Saheed Olayemi Bolarinwa
> Sent: 10 July 2020 22:20
> To: helgaas@...nel.org
> From: Bolarinwa Olayemi Saheed <refactormyself@...il.com>
> 
> On failure pcie_capability_read_dword() sets it's last parameter,
> val to 0.
> However, with Patch 14/14, it is possible that val is set to ~0 on
> failure. This would introduce a bug because (x & x) == (~0 & x).
> 
> This bug can be avoided if the return value of pcie_capability_read_dword
> is checked to confirm success.
> 
> Check the return value of pcie_capability_read_dword() to ensure success.
> 
> Suggested-by: Bjorn Helgaas <bjorn@...gaas.com>
> Signed-off-by: Bolarinwa Olayemi Saheed <refactormyself@...il.com>
> ---
>  drivers/pci/pci.c | 52 ++++++++++++++++++++++++++++++-----------------
>  1 file changed, 33 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index ce096272f52b..9f18ffbf7bd4 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3207,6 +3207,7 @@ void pci_configure_ari(struct pci_dev *dev)
>  {
>  	u32 cap;
>  	struct pci_dev *bridge;
> +	int ret;
> 
>  	if (pcie_ari_disabled || !pci_is_pcie(dev) || dev->devfn)
>  		return;
> @@ -3215,8 +3216,8 @@ void pci_configure_ari(struct pci_dev *dev)
>  	if (!bridge)
>  		return;
> 
> -	pcie_capability_read_dword(bridge, PCI_EXP_DEVCAP2, &cap);
> -	if (!(cap & PCI_EXP_DEVCAP2_ARI))
> +	ret = pcie_capability_read_dword(bridge, PCI_EXP_DEVCAP2, &cap);
> +	if (ret || !(cap & PCI_EXP_DEVCAP2_ARI))
>  		return;

Why not make the function result 64bit?
Then you can return ~0ull on failure and the capability value on success.
Gets rid of the horrid error + return value pair.

	David

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