* [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking
@ 2019-10-10 12:47 ` Bjorn Helgaas
0 siblings, 0 replies; 10+ messages in thread
From: Bjorn Helgaas @ 2019-10-10 12:47 UTC (permalink / raw)
To: linux-pci
Cc: Sagi Grimberg, Mario Limonciello, linux-pm, Rafael J . Wysocki,
linux-kernel, linux-nvme, Keith Busch, Kai-Heng Feng,
Bjorn Helgaas, Rajat Jain, Christoph Hellwig, Heiner Kallweit
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
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^ permalink raw reply related [flat|nested] 10+ messages in thread* Re: [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking
2019-10-10 12:47 ` Bjorn Helgaas
@ 2019-10-10 14:01 ` Christoph Hellwig
-1 siblings, 0 replies; 10+ 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] 10+ messages in thread
* Re: [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking
@ 2019-10-10 14:01 ` Christoph Hellwig
0 siblings, 0 replies; 10+ messages in thread
From: Christoph Hellwig @ 2019-10-10 14:01 UTC (permalink / raw)
To: Bjorn Helgaas
Cc: Sagi Grimberg, Mario Limonciello, linux-pci, linux-pm,
Rafael J . Wysocki, linux-kernel, linux-nvme, Keith Busch,
Kai-Heng Feng, Bjorn Helgaas, Rajat Jain, Christoph Hellwig,
Heiner Kallweit
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;
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http://lists.infradead.org/mailman/listinfo/linux-nvme
^ permalink raw reply [flat|nested] 10+ 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
-1 siblings, 0 replies; 10+ 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] 10+ messages in thread* Re: [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking
@ 2019-10-10 16:14 ` Bjorn Helgaas
0 siblings, 0 replies; 10+ messages in thread
From: Bjorn Helgaas @ 2019-10-10 16:14 UTC (permalink / raw)
To: Christoph Hellwig
Cc: Sagi Grimberg, Mario Limonciello, linux-pci, linux-pm,
Rafael J . Wysocki, linux-kernel, linux-nvme, Keith Busch,
Kai-Heng Feng, Rajat Jain, Heiner Kallweit
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;
}
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^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking
2019-10-10 12:47 ` Bjorn Helgaas
@ 2019-10-10 16:28 ` Rafael J. Wysocki
-1 siblings, 0 replies; 10+ 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] 10+ messages in thread* Re: [PATCH 1/1] PCI/ASPM: Remove pcie_aspm_enabled() unnecessary locking
@ 2019-10-10 16:28 ` Rafael J. Wysocki
0 siblings, 0 replies; 10+ messages in thread
From: Rafael J. Wysocki @ 2019-10-10 16:28 UTC (permalink / raw)
To: Bjorn Helgaas
Cc: Sagi Grimberg, Mario Limonciello, Linux PCI, Linux PM,
Rafael J . Wysocki, Linux Kernel Mailing List, linux-nvme,
Keith Busch, Kai-Heng Feng, Bjorn Helgaas, Rajat Jain,
Christoph Hellwig, Heiner Kallweit
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
>
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^ permalink raw reply [flat|nested] 10+ messages in thread