linux-kernel - [PATCH 1/1] PCI/ASPM: Remove pcie_aspm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 10 Oct 2019 07:47:46 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     linux-pci@...r.kernel.org
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Sagi Grimberg <sagi@...mberg.me>,
        Mario Limonciello <Mario.Limonciello@...l.com>,
        Keith Busch <keith.busch@...el.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Rajat Jain <rajatja@...gle.com>,
        Christoph Hellwig <hch@....de>,
        Heiner Kallweit <hkallweit1@...il.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking

From: Bjorn Helgaas <bhelgaas@...gle.com>

The lifetime of the link_state structure (bridge->link_state) is not the
same as the lifetime of "bridge" itself.  The link_state is allocated by
pcie_aspm_init_link_state() after children of the bridge have been
enumerated, and it is deallocated by pcie_aspm_exit_link_state() after all
children of the bridge (but not the bridge itself) have been removed.

Previously pcie_aspm_enabled() acquired aspm_lock to ensure that
link_state was not deallocated while we're looking at it.  But the fact
that the caller of pcie_aspm_enabled() holds a reference to @pdev means
there's always at least one child of the bridge, which means link_state
can't be deallocated.

Remove the unnecessary locking in pcie_aspm_enabled().

Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
---
 drivers/pci/pcie/aspm.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 652ef23bba35..f5c7138a34aa 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -1172,20 +1172,20 @@ module_param_call(policy, pcie_aspm_set_policy, pcie_aspm_get_policy,
 /**
  * pcie_aspm_enabled - Check if PCIe ASPM has been enabled for a device.
  * @pdev: Target device.
+ *
+ * Relies on the upstream bridge's link_state being valid.  The link_state
+ * is deallocated only when the last child of the bridge (i.e., @pdev or a
+ * sibling) is removed, and the caller should be holding a reference to
+ * @pdev, so this should be safe.
  */
 bool pcie_aspm_enabled(struct pci_dev *pdev)
 {
 	struct pci_dev *bridge = pci_upstream_bridge(pdev);
-	bool ret;
 
 	if (!bridge)
 		return false;
 
-	mutex_lock(&aspm_lock);
-	ret = bridge->link_state ? !!bridge->link_state->aspm_enabled : false;
-	mutex_unlock(&aspm_lock);
-
-	return ret;
+	return bridge->link_state ? !!bridge->link_state->aspm_enabled : false;
 }
 EXPORT_SYMBOL_GPL(pcie_aspm_enabled);
 
-- 
2.23.0.581.g78d2f28ef7-goog