linux-kernel - pcie aspm link setup, grandparent instead of parent?

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Message-ID: <20130612172132.GG27284@hpx.cz>
Date:	Wed, 12 Jun 2013 19:21:32 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>
Cc:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
Subject: pcie aspm link setup, grandparent instead of parent?

Hello,

as a consequence of hitting a NULL dereference bug[1] while downstream
aspm is setting up link_state, I started to wonder why is the code
skipping its parent bus in favour of grandparent's link_state.[2]

Is this right? (I have no device to test on ...)

Thanks.

---
1: https://bugzilla.redhat.com/show_bug.cgi?id=972381
   The bug is hit because "pdev->bus->parent" has NULL "->parent" and thus
   NULL "->self".
2: "pdev = bus->self", so "pdev->bus->parent == bus->parent->parent"


diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 403a443..d58e282 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -527,7 +527,7 @@ static struct pcie_link_state *alloc_pcie_link_state(struct pci_dev *pdev)
 	link->pdev = pdev;
 	if (pci_pcie_type(pdev) == PCI_EXP_TYPE_DOWNSTREAM) {
 		struct pcie_link_state *parent;
-		parent = pdev->bus->parent->self->link_state;
+		parent = pdev->bus->self->link_state;
 		if (!parent) {
 			kfree(link);
 			return NULL;
--
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