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

Manivannan Sadhasivam
2023-11-17T10:29:13Z

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@linaro.org>
> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>

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

- 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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