Re: [PATCH 1/6] PCI/ASPM: Add locked helper for enabling link state

[Manivannan Sadhasivam]

On Tue, Nov 14, 2023 at 02:55:48PM +0100, Johan Hovold wrote:
> Add a helper for enabling link states that can be used in contexts where
> a pci_bus_sem read lock is already held (e.g. from pci_walk_bus()).
> 
> This helper will be used to fix a couple of potential deadlocks where
> the current helper is called with the lock already held, hence the CC
> stable tag.
> 
> Fixes: f492edb40b54 ("PCI: vmd: Add quirk to configure PCIe ASPM and LTR")
> Cc: stable@xxxxxxxxxxxxxxx	# 6.3
> Cc: Michael Bottini <michael.a.bottini@xxxxxxxxxxxxxxx>
> Cc: David E. Box <david.e.box@xxxxxxxxxxxxxxx>
> Signed-off-by: Johan Hovold <johan+linaro@xxxxxxxxxx>

With the Kdoc comment fixed,

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>

- Mani

> ---
>  drivers/pci/pcie/aspm.c | 53 +++++++++++++++++++++++++++++++----------
>  include/linux/pci.h     |  3 +++
>  2 files changed, 43 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 50b04ae5c394..8cf8cc2d6bba 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -1109,17 +1109,7 @@ int pci_disable_link_state(struct pci_dev *pdev, int state)
>  }
>  EXPORT_SYMBOL(pci_disable_link_state);
>  
> -/**
> - * pci_enable_link_state - Clear and set the default device link state so that
> - * the link may be allowed to enter the specified states. Note that if the
> - * BIOS didn't grant ASPM control to the OS, this does nothing because we can't
> - * touch the LNKCTL register. Also note that this does not enable states
> - * disabled by pci_disable_link_state(). Return 0 or a negative errno.
> - *
> - * @pdev: PCI device
> - * @state: Mask of ASPM link states to enable
> - */
> -int pci_enable_link_state(struct pci_dev *pdev, int state)
> +static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
>  {
>  	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
>  
> @@ -1136,7 +1126,8 @@ int pci_enable_link_state(struct pci_dev *pdev, int state)
>  		return -EPERM;
>  	}
>  
> -	down_read(&pci_bus_sem);
> +	if (!locked)
> +		down_read(&pci_bus_sem);
>  	mutex_lock(&aspm_lock);
>  	link->aspm_default = 0;
>  	if (state & PCIE_LINK_STATE_L0S)
> @@ -1157,12 +1148,48 @@ int pci_enable_link_state(struct pci_dev *pdev, int state)
>  	link->clkpm_default = (state & PCIE_LINK_STATE_CLKPM) ? 1 : 0;
>  	pcie_set_clkpm(link, policy_to_clkpm_state(link));
>  	mutex_unlock(&aspm_lock);
> -	up_read(&pci_bus_sem);
> +	if (!locked)
> +		up_read(&pci_bus_sem);
>  
>  	return 0;
>  }
> +
> +/**
> + * pci_enable_link_state - Clear and set the default device link state so that
> + * the link may be allowed to enter the specified states. Note that if the
> + * BIOS didn't grant ASPM control to the OS, this does nothing because we can't
> + * touch the LNKCTL register. Also note that this does not enable states
> + * disabled by pci_disable_link_state(). Return 0 or a negative errno.
> + *
> + * @pdev: PCI device
> + * @state: Mask of ASPM link states to enable
> + */
> +int pci_enable_link_state(struct pci_dev *pdev, int state)
> +{
> +	return __pci_enable_link_state(pdev, state, false);
> +}
>  EXPORT_SYMBOL(pci_enable_link_state);
>  
> +/**
> + * pci_enable_link_state - Clear and set the default device link state so that
> + * the link may be allowed to enter the specified states. Note that if the
> + * BIOS didn't grant ASPM control to the OS, this does nothing because we can't
> + * touch the LNKCTL register. Also note that this does not enable states
> + * disabled by pci_disable_link_state(). Return 0 or a negative errno.
> + *
> + * @pdev: PCI device
> + * @state: Mask of ASPM link states to enable
> + *
> + * Context: Caller holds pci_bus_sem read lock.
> + */
> +int pci_enable_link_state_locked(struct pci_dev *pdev, int state)
> +{
> +	lockdep_assert_held_read(&pci_bus_sem);
> +
> +	return __pci_enable_link_state(pdev, state, true);
> +}
> +EXPORT_SYMBOL(pci_enable_link_state_locked);
> +
>  static int pcie_aspm_set_policy(const char *val,
>  				const struct kernel_param *kp)
>  {
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 60ca768bc867..dea043bc1e38 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1829,6 +1829,7 @@ extern bool pcie_ports_native;
>  int pci_disable_link_state(struct pci_dev *pdev, int state);
>  int pci_disable_link_state_locked(struct pci_dev *pdev, int state);
>  int pci_enable_link_state(struct pci_dev *pdev, int state);
> +int pci_enable_link_state_locked(struct pci_dev *pdev, int state);
>  void pcie_no_aspm(void);
>  bool pcie_aspm_support_enabled(void);
>  bool pcie_aspm_enabled(struct pci_dev *pdev);
> @@ -1839,6 +1840,8 @@ static inline int pci_disable_link_state_locked(struct pci_dev *pdev, int state)
>  { return 0; }
>  static inline int pci_enable_link_state(struct pci_dev *pdev, int state)
>  { return 0; }
> +static inline int pci_enable_link_state_locked(struct pci_dev *pdev, int state)
> +{ return 0; }
>  static inline void pcie_no_aspm(void) { }
>  static inline bool pcie_aspm_support_enabled(void) { return false; }
>  static inline bool pcie_aspm_enabled(struct pci_dev *pdev) { return false; }
> -- 
> 2.41.0
> 

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