[Linux-kernel-mentees] [PATCH 1/14 v3] IB/hfi1: Check the return value of pcie_capability_read_*()

From: "Saheed O. Bolarinwa" <refactormyself@gmail.com>
To: skhan@linuxfoundation.org, linux-rdma@vger.kernel.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	linux-kernel@vger.kernel.org
Cc: Bolarinwa Olayemi Saheed <refactormyself@gmail.com>
Subject: [Linux-kernel-mentees] [PATCH 1/14 v3] IB/hfi1: Check the return value of pcie_capability_read_*()
Date: Mon, 13 Jul 2020 19:55:25 +0200	[thread overview]
Message-ID: <20200713175529.29715-1-refactormyself@gmail.com> (raw)

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
--- a/drivers/infiniband/hw/hfi1/aspm.c
+++ 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;
 }
 
 /* Set L1 entrance latency for slower entry to L1 */
-- 
2.18.2

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