[PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking

Bjorn Helgaas
2019-10-10T12:48:02Z

From: Bjorn Helgaas <bhelgaas@google.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@google.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