linux-kernel - [PATCH 3/6] PCI: qcom: Fix deadlock when enabling ASPM

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Date:   Tue, 14 Nov 2023 14:55:50 +0100
From:   Johan Hovold <johan+linaro@...nel.org>
To:     Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Nirmal Patel <nirmal.patel@...ux.intel.com>,
        Jonathan Derrick <jonathan.derrick@...ux.dev>,
        linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Johan Hovold <johan+linaro@...nel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: [PATCH 3/6] PCI: qcom: Fix deadlock when enabling ASPM

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