| Message ID | 20191010124746.2882-2-helgaas@kernel.org (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
| Series | PCI/ASPM: Remove locking | expand |
On Thu, Oct 10, 2019 at 07:47:46AM -0500, Bjorn Helgaas wrote:
> + return bridge->link_state ? !!bridge->link_state->aspm_enabled : false;
Can we unobsfucated this while we're at it?
if (!bridge->link_state)
return false;
return bridge->link_state->aspm_enabled;
On Thu, Oct 10, 2019 at 04:01:21PM +0200, Christoph Hellwig wrote: > On Thu, Oct 10, 2019 at 07:47:46AM -0500, Bjorn Helgaas wrote: > > + return bridge->link_state ? !!bridge->link_state->aspm_enabled : false; > > Can we unobsfucated this while we're at it? > > if (!bridge->link_state) > return false; > return bridge->link_state->aspm_enabled; Yep, after some of the follow-up patches from Heiner, it looks like this: bool pcie_aspm_enabled(struct pci_dev *pdev) { struct pcie_link_state *link = pcie_aspm_get_link(pdev); if (!link) return false; return link->aspm_enabled; }
On Thu, Oct 10, 2019 at 2:48 PM Bjorn Helgaas <helgaas@kernel.org> wrote: > > 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> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> (also for the further changes you and Christoph have been discussing). > --- > 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 >
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);