Re: [PATCH 3/6] PCI: qcom: Fix deadlock when enabling ASPM

[Manivannan Sadhasivam]

On Tue, Nov 14, 2023 at 02:55:50PM +0100, Johan Hovold wrote:
> The qcom_pcie_enable_aspm() helper is called from pci_walk_bus() during
> host init to enable ASPM.
> 
> Since pci_walk_bus() already holds a pci_bus_sem read lock, use the new
> locked helper to enable link states in order to avoid a potential
> deadlock (e.g. in case someone takes a write lock before reacquiring
> the read lock).
> 
> This issue was reported by lockdep:
> 
>    ============================================
>    WARNING: possible recursive locking detected
>    6.7.0-rc1 #4 Not tainted
>    --------------------------------------------
>    kworker/u16:6/147 is trying to acquire lock:
>    ffffbf3ff9d2cfa0 (pci_bus_sem){++++}-{3:3}, at: pci_enable_link_state+0x74/0x1e8
> 
>    but task is already holding lock:
>    ffffbf3ff9d2cfa0 (pci_bus_sem){++++}-{3:3}, at: pci_walk_bus+0x34/0xbc
> 
>    other info that might help us debug this:
>     Possible unsafe locking scenario:
> 
>           CPU0
>           ----
>      lock(pci_bus_sem);
>      lock(pci_bus_sem);
> 
>     *** DEADLOCK ***
> 
> Fixes: 9f4f3dfad8cf ("PCI: qcom: Enable ASPM for platforms supporting 1.9.0 ops")
> Cc: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> Signed-off-by: Johan Hovold <johan+linaro@xxxxxxxxxx>

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

- Mani

> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index ce3ece28fed2..21523115f6a4 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -971,7 +971,7 @@ static int qcom_pcie_enable_aspm(struct pci_dev *pdev, void *userdata)
>  {
>  	/* Downstream devices need to be in D0 state before enabling PCI PM substates */
>  	pci_set_power_state(pdev, PCI_D0);
> -	pci_enable_link_state(pdev, PCIE_LINK_STATE_ALL);
> +	pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
>  
>  	return 0;
>  }
> -- 
> 2.41.0
> 

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