PCI/ASPM: Fix deadlock when enabling ASPM

In the Linux kernel, the following vulnerability has been resolved:

PCI/ASPM: Fix deadlock when enabling ASPM

A last minute revert in 6.7-final introduced a potential deadlock when

enabling ASPM during probe of Qualcomm PCIe controllers as reported by

lockdep:

============================================

WARNING: possible recursive locking detected

6.7.0 #40 Not tainted

--------------------------------------------

kworker/u16:5/90 is trying to acquire lock:

ffffacfa78ced000 (pci_bus_sem){++++}-{3:3}, at: pcie_aspm_pm_state_change+0x58/0xdc

but task is already holding lock:

ffffacfa78ced000 (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 ***

Call trace:

print_deadlock_bug+0x25c/0x348

__lock_acquire+0x10a4/0x2064

lock_acquire+0x1e8/0x318

down_read+0x60/0x184

pcie_aspm_pm_state_change+0x58/0xdc

pci_set_full_power_state+0xa8/0x114

pci_set_power_state+0xc4/0x120

qcom_pcie_enable_aspm+0x1c/0x3c [pcie_qcom]

pci_walk_bus+0x64/0xbc

qcom_pcie_host_post_init_2_7_0+0x28/0x34 [pcie_qcom]

The deadlock can easily be reproduced on machines like the Lenovo ThinkPad

X13s by adding a delay to increase the race window during asynchronous

probe where another thread can take a write lock.

Add a new pci_set_power_state_locked() and associated helper functions that

can be called with the PCI bus semaphore held to avoid taking the read lock

twice.