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Date:   Mon, 13 Jul 2020 14:09:41 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     "Saheed O. Bolarinwa" <refactormyself@gmail.com>
Cc:     skhan@linuxfoundation.org, linux-rdma@vger.kernel.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/14 v3] IB/hfi1: Check the return value of
 pcie_capability_read_*()
Message-ID: <20200713170941.GB25301@ziepe.ca>
References: <20200713175529.29715-1-refactormyself@gmail.com>
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On Mon, Jul 13, 2020 at 07:55:25PM +0200, Saheed O. Bolarinwa wrote:
> From: Bolarinwa Olayemi Saheed <refactormyself@gmail.com>
> 
> On failure pcie_capability_read_dword() sets it's last parameter,
> val to 0. In this case dn and up will be 0, so aspm_hw_l1_supported()
> will return false.
> 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). So with
> dn and up being 0x02, a true value is return when the read has actually
> failed.
> 
> This bug can be avoided if the return value of pcie_capability_read_dword
> is checked to confirm success. The behaviour of the function remains
> intact.
> 
> Check the return value of pcie_capability_read_dword() to ensure success.
> 
> Suggested-by: Bjorn Helgaas <bjorn@helgaas.com>
> Signed-off-by: Bolarinwa Olayemi Saheed <refactormyself@gmail.com>
>  drivers/infiniband/hw/hfi1/aspm.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/hfi1/aspm.c b/drivers/infiniband/hw/hfi1/aspm.c
> index a3c53be4072c..80d0b3edd983 100644
> +++ b/drivers/infiniband/hw/hfi1/aspm.c
> @@ -24,6 +24,7 @@ static bool aspm_hw_l1_supported(struct hfi1_devdata *dd)
>  {
>  	struct pci_dev *parent = dd->pcidev->bus->self;
>  	u32 up, dn;
> +	int ret_up, ret_dn;
>  
>  	/*
>  	 * If the driver does not have access to the upstream component,
> @@ -32,14 +33,14 @@ static bool aspm_hw_l1_supported(struct hfi1_devdata *dd)
>  	if (!parent)
>  		return false;
>  
> -	pcie_capability_read_dword(dd->pcidev, PCI_EXP_LNKCAP, &dn);
> +	ret_dn = pcie_capability_read_dword(dd->pcidev, PCI_EXP_LNKCAP, &dn);
>  	dn = ASPM_L1_SUPPORTED(dn);
>  
> -	pcie_capability_read_dword(parent, PCI_EXP_LNKCAP, &up);
> +	ret_up = pcie_capability_read_dword(parent, PCI_EXP_LNKCAP, &up);
>  	up = ASPM_L1_SUPPORTED(up);
>  
>  	/* ASPM works on A-step but is reported as not supported */
> -	return (!!dn || is_ax(dd)) && !!up;
> +	return !!ret_dn && !!ret_up && (!!dn || is_ax(dd)) && !!up;
>  }

what is all the !! for? boolean contexts already coerce to boolean

Jason