CVE-2024-26605: 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 (pcibussem){++++}-{3:3}, at: pcieaspmpmstatechange+0x58/0xdc

but task is already holding lock: ffffacfa78ced000 (pcibussem){++++}-{3:3}, at: pciwalkbus+0x34/0xbc

other info that might help us debug this: Possible unsafe locking scenario:

CPU0 ---- lock(pcibussem); lock(pcibussem);

DEADLOCK

Call trace: printdeadlockbug+0x25c/0x348 lockacquire+0x10a4/0x2064 lockacquire+0x1e8/0x318 downread+0x60/0x184 pcieaspmpmstatechange+0x58/0xdc pcisetfullpowerstate+0xa8/0x114 pcisetpowerstate+0xc4/0x120 qcompcieenableaspm+0x1c/0x3c [pcieqcom] pciwalkbus+0x64/0xbc qcompciehostpostinit270+0x28/0x34 [pcieqcom]

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 pcisetpowerstatelocked() and associated helper functions that can be called with the PCI bus semaphore held to avoid taking the read lock twice.