[PATCH 3/7][SRU][Focal] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking

AceLan Kao acelan.kao at canonical.com
Tue Mar 10 01:48:32 UTC 2020

From: Bjorn Helgaas <bhelgaas at google.com>

BugLink: https://bugs.launchpad.net/bugs/1836030

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 at google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
(cherry picked from commit 5e0c21c75e8c08375a69710527e4a921b897cb7e)
Signed-off-by: AceLan Kao <acelan.kao at canonical.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 a602c51c932f..23e1d6b88655 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -1185,20 +1185,20 @@ 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;

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