* [PATCH 0/1] PCI/ASPM: Remove locking @ 2019-10-10 12:47 Bjorn Helgaas 2019-10-10 12:47 ` [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking Bjorn Helgaas 0 siblings, 1 reply; 5+ messages in thread From: Bjorn Helgaas @ 2019-10-10 12:47 UTC (permalink / raw) To: linux-pci Cc: Rafael J . Wysocki, Sagi Grimberg, Mario Limonciello, Keith Busch, Kai-Heng Feng, Rajat Jain, Christoph Hellwig, Heiner Kallweit, linux-pm, linux-kernel, linux-nvme, Bjorn Helgaas From: Bjorn Helgaas <bhelgaas@google.com> In reference to this thread: https://lore.kernel.org/r/20191007223428.GA72605@google.com This removes locking from pcie_aspm_enabled() because the reference count held by the driver should provide all the locking we need. Bjorn Helgaas (1): PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking drivers/pci/pcie/aspm.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) -- 2.23.0.581.g78d2f28ef7-goog ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking 2019-10-10 12:47 [PATCH 0/1] PCI/ASPM: Remove locking Bjorn Helgaas @ 2019-10-10 12:47 ` Bjorn Helgaas 2019-10-10 14:01 ` Christoph Hellwig 2019-10-10 16:28 ` Rafael J. Wysocki 0 siblings, 2 replies; 5+ messages in thread From: Bjorn Helgaas @ 2019-10-10 12:47 UTC (permalink / raw) To: linux-pci Cc: Rafael J . Wysocki, Sagi Grimberg, Mario Limonciello, Keith Busch, Kai-Heng Feng, Rajat Jain, Christoph Hellwig, Heiner Kallweit, linux-pm, linux-kernel, linux-nvme, Bjorn Helgaas 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 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking 2019-10-10 12:47 ` [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking Bjorn Helgaas @ 2019-10-10 14:01 ` Christoph Hellwig 2019-10-10 16:14 ` Bjorn Helgaas 2019-10-10 16:28 ` Rafael J. Wysocki 1 sibling, 1 reply; 5+ messages in thread From: Christoph Hellwig @ 2019-10-10 14:01 UTC (permalink / raw) To: Bjorn Helgaas Cc: linux-pci, Rafael J . Wysocki, Sagi Grimberg, Mario Limonciello, Keith Busch, Kai-Heng Feng, Rajat Jain, Christoph Hellwig, Heiner Kallweit, linux-pm, linux-kernel, linux-nvme, Bjorn Helgaas 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; ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking 2019-10-10 14:01 ` Christoph Hellwig @ 2019-10-10 16:14 ` Bjorn Helgaas 0 siblings, 0 replies; 5+ messages in thread From: Bjorn Helgaas @ 2019-10-10 16:14 UTC (permalink / raw) To: Christoph Hellwig Cc: linux-pci, Rafael J . Wysocki, Sagi Grimberg, Mario Limonciello, Keith Busch, Kai-Heng Feng, Rajat Jain, Heiner Kallweit, linux-pm, linux-kernel, linux-nvme 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; } ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking 2019-10-10 12:47 ` [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking Bjorn Helgaas 2019-10-10 14:01 ` Christoph Hellwig @ 2019-10-10 16:28 ` Rafael J. Wysocki 1 sibling, 0 replies; 5+ messages in thread From: Rafael J. Wysocki @ 2019-10-10 16:28 UTC (permalink / raw) To: Bjorn Helgaas Cc: Linux PCI, Rafael J . Wysocki, Sagi Grimberg, Mario Limonciello, Keith Busch, Kai-Heng Feng, Rajat Jain, Christoph Hellwig, Heiner Kallweit, Linux PM, Linux Kernel Mailing List, linux-nvme, Bjorn Helgaas 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 > ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2019-10-10 16:28 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-10-10 12:47 [PATCH 0/1] PCI/ASPM: Remove locking Bjorn Helgaas 2019-10-10 12:47 ` [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking Bjorn Helgaas 2019-10-10 14:01 ` Christoph Hellwig 2019-10-10 16:14 ` Bjorn Helgaas 2019-10-10 16:28 ` Rafael J. Wysocki
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