tree 05668a16f75570f3a408b762ea2462180cb26a30
parent 53762ba810398c11efaf65f9a45d992125e86dcf
author Bjorn Helgaas <bhelgaas@google.com> 1484352312 -0600
committer Bjorn Helgaas <bhelgaas@google.com> 1485816933 -0600

PCI: Avoid possible deadlock on pci_lock and p->pi_lock

pci_lock is an IRQ-safe spinlock that protects all accesses to PCI
configuration space (see PCI_OP_READ() and PCI_OP_WRITE() in pci/access.c).

The pci_cfg_access_unlock() path acquires pci_lock, then p->pi_lock (inside
wake_up_all()).  According to lockdep, there is a possible path involving
snbep_uncore_pci_read_counter() that could acquire them in the reverse
order: acquiring p->pi_lock, then pci_lock, which could result in a
deadlock.  Lockdep details are in the bugzilla below.

Avoid the possible deadlock by dropping pci_lock before waking up any
config access waiters.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=192901
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>