[PATCH iwl-net v2 1/2] igc: don't disable ASPM L1.2 from __igc_resume()

[Daniel Viaño]

Commit 0325143b59c6 ("igc: disable L1.2 PCI-E link substate to avoid
performance issue") disables L1.2 on I226 in probe, in __igc_resume()
and in igc_io_slot_reset(). The resume path uses
pci_disable_link_state(), which takes pci_bus_sem for read.

__igc_resume() is also the runtime resume callback, and it can be
called with pci_bus_sem already held: pcie_do_recovery() runtime-
resumes all affected devices through

  pci_walk_bridge(bridge, pci_pm_runtime_get_sync, NULL)

i.e. from within pci_walk_bus(), which holds pci_bus_sem for read. If
the igc device is runtime-suspended at that point, the call chain is

  pci_walk_bus()                      down_read(&pci_bus_sem)
    pci_pm_runtime_get_sync()
      igc_runtime_resume()
        __igc_resume()
          pci_disable_link_state()    down_read(&pci_bus_sem)

A recursive down_read() deadlocks if a writer (e.g. a hot-plug event
adding or removing a device) queues on pci_bus_sem between the two
acquisitions. pci_disable_link_state_locked() cannot be used instead,
because on the system suspend/resume and ordinary runtime resume paths
the lock is not held.

The call is not needed on resume in the first place. The disable done
in igc_probe() is recorded in the link's aspm_disable mask, which is
only cleared through the ASPM sysfs interface. The PCI core honours
that mask whenever it reconfigures the link, including when the device
returns to D0 (pcie_aspm_pm_state_change()), and pci_restore_state()
restores the L1 PM Substates control registers saved with L1.2
already disabled. Drop the call from __igc_resume().

The issue was found by the Sashiko AI review of an earlier version of
this series.

Fixes: 0325143b59c6 ("igc: disable L1.2 PCI-E link substate to avoid performance issue")
Signed-off-by: Daniel Viaño <danividanivi@xxxxxxxxx>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 62a7c5178..1b5dcc166 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -7585,9 +7585,6 @@ static int __igc_resume(struct device *dev, bool rpm)
 	pci_enable_wake(pdev, PCI_D3hot, 0);
 	pci_enable_wake(pdev, PCI_D3cold, 0);
 
-	if (igc_is_device_id_i226(hw))
-		pci_disable_link_state(pdev, PCIE_LINK_STATE_L1_2);
-
 	if (igc_init_interrupt_scheme(adapter, true)) {
 		netdev_err(netdev, "Unable to allocate memory for queues\n");
 		return -ENOMEM;
-- 
2.53.0