Commit cdcb33f9 authored Jan 13, 2017 by Bjorn Helgaas

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>

parent 53762ba8

drivers/pci/access.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -684,8 +684,9 @@ void pci_cfg_access_unlock(struct pci_dev *dev)
		WARN_ON(!dev->block_cfg_access);

		dev->block_cfg_access = 0;
		wake_up_all(&pci_cfg_wait);
		raw_spin_unlock_irqrestore(&pci_lock, flags);

		wake_up_all(&pci_cfg_wait);
		}
		EXPORT_SYMBOL_GPL(pci_cfg_access_unlock);

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