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PCI: qcom: Fix potential deadlock when enabling ASPM
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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
pci_enable_link_state_locked() 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: 9f4f3df ("PCI: qcom: Enable ASPM for platforms supporting 1.9.0 ops")
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Johan Hovold <[email protected]>
[bhelgaas: add "potential" in subject since the deadlock has only been
reported by lockdep, include helper name in commit log]
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Manivannan Sadhasivam <[email protected]>
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jhovold authored and bjorn-helgaas committed Dec 11, 2023
1 parent 49de0dc commit f352ce9
Showing 1 changed file with 1 addition and 1 deletion.
2 changes: 1 addition & 1 deletion drivers/pci/controller/dwc/pcie-qcom.c
Original file line number Diff line number Diff line change
Expand Up @@ -970,7 +970,7 @@ 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;
}
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